diff --git a/keymaster/4.0/IKeymasterDevice.hal b/keymaster/4.0/IKeymasterDevice.hal
index aef81c7..6c09ef3 100644
--- a/keymaster/4.0/IKeymasterDevice.hal
+++ b/keymaster/4.0/IKeymasterDevice.hal
@@ -20,46 +20,234 @@
 import android.hardware.keymaster@3.0::KeyFormat;
 
 /**
- * Keymaster device definition.  For thorough documentation see the implementer's reference, at
- * https://source.android.com/security/keystore/implementer-ref.html
+ * Keymaster device definition.
+ *
+ * == Features ==
+ *
+ * An IKeymasterDevice provides cryptographic services, including the following categories of
+ * operations:
+ *
+ * o   Key generation
+ * o   Import and export (public only) of asymmetric keys
+ * o   Import of raw symmetric keys
+ * o   Asymmetric encryption and decryption with appropriate padding modes
+ * o   Asymmetric signing and verification with digesting and appropriate padding modes
+ * o   Symmetric encryption and decryption in appropriate modes, including an AEAD mode
+ * o   Generation and verification of symmetric message authentication codes
+ * o   Attestation to the presence and configuration of asymmetric keys.
+ *
+ * Protocol elements, such as purpose, mode and padding, as well as access control constraints, must
+ * be specified by the caller when keys are generated or imported and must be permanently bound to
+ * the key, ensuring that the key cannot be used in any other way.
+ *
+ * In addition to the list above, IKeymasterDevice implementations must provide one more service
+ * which is not exposed as an API but used internally: Random number generation.  The random number
+ * generator must be high-quality and must be used for generation of keys, initialization vectors,
+ * random padding and other elements of secure protocols that require randomness.
+ *
+ * == Types of IKeymasterDevices ==
+ *
+ * All of the operations and storage of key material must occur in a secure environment.  Secure
+ * environments may be either:
+ *
+ * 1.  Isolated execution environments, such as a separate virtual machine, hypervisor or
+ *      purpose-built trusted execution environment like ARM TrustZone.  The isolated environment
+ *      must provide complete separation from the Android kernel and user space (collectively called
+ *      the "non-secure world", or NSW) so that nothing running in the NSW can observe or manipulate
+ *      the results of any computation in the isolated environment.  Isolated execution environments
+ *      are identified by the SecurityLevel TRUSTED_ENVIRONMENT.
+ *
+ * 2.  Completely separate, purpose-built and certified secure CPUs, called "StrongBox" devices.
+ *      Examples of StrongBox devices are embedded Secure Elements (eSE) or on-SoC secure processing
+ *      units (SPU).  StrongBox environments are identified by the SecurityLevel STRONGBOX.  To
+ *      qualify as a StrongBox, a device must meet the requirements specified in CDD 9.11.2.
+ *
+ * == Necessary Primitives ==
+ *
+ * All IKeymasterDevice implementations must provide support for the following:
+ *
+ * o   RSA
+ *
+ *      - TRUSTED_ENVIRONMENT IKeymasterDevices must support 2048, 3072 and 4096-bit keys.
+ *        STRONGBOX IKeymasterDevices must support 2048-bit keys.
+ *      - Public exponent F4 (2^16+1)
+ *      - Unpadded, RSASSA-PSS and RSASSA-PKCS1-v1_5 padding modes for RSA signing
+ *      - TRUSTED_ENVIRONMENT IKeymasterDevices must support MD5, SHA1, SHA-2 224, SHA-2 256, SHA-2
+ *        384 and SHA-2 512 digest modes for RSA signing.  STRONGBOX IKeymasterDevices must support
+ *        SHA-2 256.
+ *      - Unpadded, RSAES-OAEP and RSAES-PKCS1-v1_5 padding modes for RSA encryption.
+ *
+ * o   ECDSA
+ *
+ *      - TRUSTED_ENVIRONMENT IKeymasterDevices must support NIST curves P-224, P-256, P-384 and
+ *        P-521.  STRONGBOX IKeymasterDevices must support NIST curve P-256.
+ *      - TRUSTED_ENVIRONMENT IKeymasterDevices must support SHA1, SHA-2 224, SHA-2 256, SHA-2
+ *        384 and SHA-2 512 digest modes.  STRONGBOX IKeymasterDevices must support SHA-2 256.
+ *
+ * o   AES
+ *
+ *      - 128 and 256-bit keys
+ *      - CBC, CTR, ECB and GCM modes.  The GCM mode must not allow the use of tags smaller than 96
+ *        bits or nonce lengths other than 96 bits.
+ *      - CBC and ECB modes must support unpadded and PKCS7 padding modes.  With no padding CBC and
+ *        ECB-mode operations must fail with ErrorCode::INVALID_INPUT_LENGTH if the input isn't a
+ *        multiple of the AES block size.  With PKCS7 padding, GCM and CTR operations must fail with
+ *        ErrorCode::INCOMPATIBLE_PADDING_MODE.
+ *
+ * o   3DES
+ *
+ *      - 168-bit keys.
+ *      - CBC and ECB mode.
+
+ *      - CBC and ECB modes must support unpadded and PKCS7 padding modes.  With no padding CBC and
+ *        ECB-mode operations must fail with ErrorCode::INVALID_INPUT_LENGTH if the input isn't a
+ *        multiple of the DES block size.
+ *
+ * o   HMAC
+ *
+ *      - Any key size that is between 64 and 512 bits (inclusive) and a multiple of 8 must be
+ *        supported.  STRONGBOX IKeymasterDevices must not support keys larger than 512 bits.
+ *      - TRUSTED_ENVIRONMENT IKeymasterDevices must support MD-5, SHA1, SHA-2-224, SHA-2-256,
+ *        SHA-2-384 and SHA-2-512.  STRONGBOX IKeymasterDevices must support SHA-2-256.
+ *
+ * == Key Access Control ==
+ *
+ * Hardware-based keys that can never be extracted from the device don't provide much security if an
+ * attacker can use them at will (though they're more secure than keys which can be
+ * exfiltrated).  Therefore, IKeymasterDevice must enforce access controls.
+ *
+ * Access controls are defined as an "authorization list" of tag/value pairs.  Authorization tags
+ * are 32-bit integers from the Tag enum, and the values are a variety of types, defined in the
+ * TagType enum.  Some tags may be repeated to specify multiple values.  Whether a tag may be
+ * repeated is specified in the documentation for the tag and in the TagType.  When a key is created
+ * or imported, the caller specifies an authorization list.  The IKeymasterDevice must divide the
+ * caller-provided authorizations into two lists, those it enforces in hardware and those it does
+ * not.  These two lists are returned as the "hardwareEnforced" and "softwareEnforced" elements of
+ * the KeyCharacteristics struct.  The IKeymasterDevice must also add the following authorizations
+ * to the appropriate list:
+ *
+ * o    Tag::OS_VERSION, must be hardware-enforced.
+ * o    Tag::OS_PATCHLEVEL, must be hardware-enforced.
+ * o    Tag::VENDOR_PATCHLEVEL, must be hardware-enforced.
+ * o    Tag::BOOT_PATCHLEVEL, must be hardware-enforced.
+ * o    Tag::CREATION_DATETIME, must be software-enforced, unless the IKeymasterDevice has access to
+ *      a secure time service.
+ * o    Tag::ORIGIN, must be hardware-enforced.
+ *
+ * The IKeymasterDevice must accept arbitrary, unknown tags and return them in the softwareEnforced
+ * list.
+ *
+ * All authorization tags and their values, both hardwareEnforced and softwareEnforced, including
+ * unknown tags, must be cryptographically bound to the private/secret key material such that any
+ * modification of the portion of the key blob that contains the authorization list makes it
+ * impossible for the secure environment to obtain the private/secret key material.  The recommended
+ * approach to meet this requirement is to use the full set of authorization tags associated with a
+ * key as input to a secure key derivation function used to derive a key that is used to encrypt the
+ * private/secret key material.
+ *
+ * IKeymasterDevice implementations must place any tags they cannot fully and completely enforce in
+ * the softwareEnforced list.  For example, Tag::ORIGINATION_EXPIRE_DATETIME provides the date and
+ * time after which a key may not be used to encrypt or sign new messages.  Unless the
+ * IKeymasterDevice has access to a secure source of current date/time information, it is not
+ * possible for the IKeymasterDevice to enforce this tag.  An IKeymasterDevice implementation may
+ * not rely on the non-secure world's notion of time, because it could be controlled by an attacker.
+ * Similarly, it cannot rely on GPSr time, even if it has exclusive control of the GPSr, because
+ * that might be spoofed by attacker RF signals.
+ *
+ * It is recommended that IKeymasterDevices not enforce any tags they place in the softwareEnforced
+ * list.  The IKeymasterDevice caller must enforce them, and it is unnecessary to enforce them
+ * twice.
+ *
+ * Some tags must be enforced by the IKeymasterDevice.  See the detailed documentation on each Tag
+ * in types.hal.
+ *
+ * == Root of Trust Binding ==
+ *
+ * IKeymasterDevice keys must be bound to a root of trust, which is a bitstring that must be
+ * provided to the secure environment (by an unspecified, implementation-defined mechanism) during
+ * startup, preferably by the bootloader.  This bitstring must be cryptographically bound to every
+ * key managed by the IKeymasterDevice.  As above, the recommended mechanism for this cryptographic
+ * binding is to include the Root of Trust data in the input to the key derivation function used to
+ * derive a key that is used to encryp the private/secret key material.
+ *
+ * The root of trust consists of a bitstring that must be derived from the public key used by
+ * Verified Boot to verify the signature on the boot image and from the the lock state of the
+ * device.  If the public key is changed to allow a different system image to be used or if the lock
+ * state is changed, then all of the IKeymasterDevice-protected keys created by the previous system
+ * state must be unusable, unless the previous state is restored.  The goal is to increase the value
+ * of the software-enforced key access controls by making it impossible for an attacker-installed
+ * operating system to use IKeymasterDevice keys.
+ *
+ * == Version Binding ==
+ *
+ * All keys must also be bound to the operating system and patch level of the system image and the
+ * patch levels of the vendor image and boot image.  This ensures that an attacker who discovers a
+ * weakness in an old version of the software cannot roll a device back to the vulnerable version
+ * and use keys created with the newer version.  In addition, when a key with a given version and
+ * patch level is used on a device that has been upgraded to a newer version or patch level, the key
+ * must be upgraded (See IKeymasterDevice::upgradeKey()) before it can be used, and the previous
+ * version of the key must be invalidated.  In this way, as the device is upgraded, the keys will
+ * "ratchet" forward along with the device, but any reversion of the device to a previous release
+ * will cause the keys to be unusable.
+ *
+ * This version information must be associated with every key as a set of tag/value pairs in the
+ * hardwareEnforced authorization list.  Tag::OS_VERSION, Tag::OS_PATCHLEVEL,
+ * Tag::VENDOR_PATCHLEVEL, and Tag::BOOT_PATCHLEVEL must be cryptographically bound to every
+ * IKeymasterDevice key, as described in the Key Access Control section above.
  */
+
 interface IKeymasterDevice {
 
     /**
-     * Returns information about the underlying Keymaster hardware.
+     * Returns information about the underlying IKeymasterDevice hardware.
      *
-     * @return security level of the Keymaster implementation accessed through this HAL.
+     * @return security level of the IKeymasterDevice implementation accessed through this HAL.
      *
-     * @return keymasterName is the name of the Keymaster implementation.
+     * @return keymasterName is the name of the IKeymasterDevice implementation.
      *
-     * @return keymasterAuthorName is the name of the author of the Keymaster implementation
+     * @return keymasterAuthorName is the name of the author of the IKeymasterDevice implementation
      *         (organization name, not individual).
      */
     getHardwareInfo()
         generates (SecurityLevel securityLevel, string keymasterName, string keymasterAuthorName);
 
     /**
-     * Start the creation of an HMAC key, shared with another Keymaster implementation.  Any device
-     * with a StrongBox Keymaster has two Keymaster instances, because there must be a TEE Keymaster
-     * as well.  The HMAC key used to MAC and verify authentication tokens must be shared between
-     * TEE and StrongBox so they can each validate tokens produced by the other.  This method is the
-     * first step in the process for for agreeing on a shared key.  It is called by Keystore during
-     * startup if and only if Keystore loads multiple Keymaster HALs.  Keystore calls it on each of
-     * the HAL instances and collects the results in preparation for the second step.
+     * Start the creation of an HMAC key, shared with another IKeymasterDevice implementation.  Any
+     * device with a StrongBox IKeymasterDevice has two IKeymasterDevice instances, because there
+     * must be a TEE Keymaster as well.  The HMAC key used to MAC and verify authentication tokens
+     * (HardwareAuthToken, VerificationToken and ConfirmationToken all use this HMAC key) must be
+     * shared between TEE and StrongBox so they can each validate tokens produced by the other.
+     * This method is the first step in the process for for agreeing on a shared key.  It is called
+     * by Android during startup.  The system calls it on each of the HAL instances and collects the
+     * results in preparation for the second step.
+     *
+     * @return error ErrorCode::OK on success, ErrorCode::UNIMPLEMENTED if HMAC agreement is not
+     *         implemented (note that all 4.0::IKeymasterDevice HALS must implement HMAC agreement,
+     *         regardless of whether or not the HAL will be used on a device with StrongBox), or
+     *         ErrorCode::UNKNOWN_ERROR if the parameters cannot be returned.
+     *
+     * @return params The HmacSharingParameters to use.  As specified in the HmacSharingParameters
+     *         documentation in types.hal, the seed must contain the same value in every invocation
+     *         of the method on a given device, and the nonce must return the same value for every
+     *         invocation during a boot session.
      */
     getHmacSharingParameters() generates (ErrorCode error, HmacSharingParameters params);
 
     /**
-     * Complete the creation of an HMAC key, shared with another Keymaster implementation.  Any
-     * device with a StrongBox Keymaster has two Keymasters instances, because there must be a TEE
-     * Keymaster as well.  The HMAC key used to MAC and verify authentication tokens must be shared
-     * between TEE and StrongBox so they can each validate tokens produced by the other.  This
-     * method is the second and final step in the process for agreeing on a shared key.  It is
-     * called by Keystore during startup if and only if Keystore loads multiple Keymaster HALs.
-     * Keystore calls it on each of the HAL instances, and sends to it all of the
-     * HmacSharingParameters returned by all HALs.
+     * Complete the creation of an HMAC key, shared with another IKeymasterDevice implementation.
+     * Any device with a StrongBox IKeymasterDevice has two IKeymasterDevice instances, because
+     * there must be a TEE IKeymasterDevice as well.  The HMAC key used to MAC and verify
+     * authentication tokens must be shared between TEE and StrongBox so they can each validate
+     * tokens produced by the other.  This method is the second and final step in the process for
+     * agreeing on a shared key.  It is called by Android during startup.  The system calls it on
+     * each of the HAL instances, and sends to it all of the HmacSharingParameters returned by all
+     * HALs.
      *
-     * This method computes the shared 32-byte HMAC ``H'' as follows (all Keymaster instances
+     * To ensure consistent ordering of the HmacSharingParameters, the caller must sort the
+     * parameters lexicographically.  See the support/keymaster_utils.cpp for an operator< that
+     * defines the appropriate ordering.
+     *
+     * This method computes the shared 32-byte HMAC ``H'' as follows (all IKeymasterDevice instances
      * perform the same computation to arrive at the same result):
      *
      *     H = CKDF(key = K,
@@ -70,25 +258,27 @@
      *
      *     ``CKDF'' is the standard AES-CMAC KDF from NIST SP 800-108 in counter mode (see Section
      *           5.1 of the referenced publication).  ``key'', ``context'', and ``label'' are
-     *           defined in the standard.  The counter is prefixed, as shown in the construction on
-     *           page 12 of the standard.  The label string is UTF-8 encoded.
+     *           defined in the standard.  The counter is prefixed and length L appended, as shown
+     *           in the construction on page 12 of the standard.  The label string is UTF-8 encoded.
      *
      *     ``K'' is a pre-established shared secret, set up during factory reset.  The mechanism for
      *           establishing this shared secret is implementation-defined, but see below for a
-     *           recommended approach, which assumes that the TEE Keymaster does not have storage
-     *           available to it, but the StrongBox Keymaster does.
+     *           recommended approach, which assumes that the TEE IKeymasterDevice does not have
+     *           storage available to it, but the StrongBox IKeymasterDevice does.
      *
-     *           <b>CRITICAL SECURITY REQUIREMENT</b>: All keys created by a Keymaster instance must
+     *           CRITICAL SECURITY REQUIREMENT: All keys created by a IKeymasterDevice instance must
      *           be cryptographically bound to the value of K, such that establishing a new K
      *           permanently destroys them.
      *
      *     ``||'' represents concatenation.
      *
      *     ``Pi'' is the i'th HmacSharingParameters value in the params vector.  Note that at
-     *           present only two Keymaster implementations are supported, but this mechanism
+     *           present only two IKeymasterDevice implementations are supported, but this mechanism
      *           extends without modification to any number of implementations.  Encoding of an
      *           HmacSharingParameters is the concatenation of its two fields, i.e. seed || nonce.
      *
+     * Note that the label "KeymasterSharedMac" is the 18-byte UTF-8 encoding of the string.
+     *
      * Process for establishing K:
      *
      *     Any method of securely establishing K that ensures that an attacker cannot obtain or
@@ -98,19 +288,19 @@
      *     have secure persistent storage.  This model was chosen because StrongBox has secure
      *     persistent storage (by definition), but the TEE may not.  The instance without storage is
      *     assumed to be able to derive a unique hardware-bound key (HBK) which is used only for
-     *     this purpose, and is not derivable outside of the secure environment..
+     *     this purpose, and is not derivable outside the secure environment.
      *
-     *     In what follows, T is the Keymaster instance without storage, S is the Keymaster instance
-     *     with storage:
+     *     In what follows, T is the IKeymasterDevice instance without storage, S is the
+     *     IKeymasterDevice instance with storage:
      *
-     *     1. T generates an ephemeral EC P-256 key pair K1
+     *     1. T generates an ephemeral EC P-256 key pair K1.
      *     2. T sends K1_pub to S, signed with T's attestation key.
      *     3. S validates the signature on K1_pub.
      *     4. S generates an ephemeral EC P-256 key pair K2.
      *     5. S sends {K1_pub, K2_pub}, to T, signed with S's attestation key.
-     *     6. T validates the signature on {K1_pub, K2_pub}
+     *     6. T validates the signature on {K1_pub, K2_pub}.
      *     7. T uses {K1_priv, K2_pub} with ECDH to compute session secret Q.
-     *     8. T generates a random seed S
+     *     8. T generates a random seed S.
      *     9. T computes K = KDF(HBK, S), where KDF is some secure key derivation function.
      *     10. T sends M = AES-GCM-ENCRYPT(Q, {S || K}) to S.
      *     10. S uses {K2_priv, K1_pub} with ECDH to compute session secret Q.
@@ -121,40 +311,54 @@
      *     T receives the computeSharedHmac call, it uses the seed provided by S to compute K.  S,
      *     of course, has K stored.
      *
-     * @param params The HmacSharingParameters data returned by all Keymaster instances when
+     * @param params The HmacSharingParameters data returned by all IKeymasterDevice instances when
      *        getHmacSharingParameters was called.
      *
-     * @return sharingCheck A 32-byte value used to verify that all Keymaster instances have
+     * @return error ErrorCode::OK in the event that there is no error.  ErrorCode::INVALID_ARGUMENT
+     *         if one of the provided parameters is not the value returned by the prior call to
+     *         getHmacParameters().
+     *
+     * @return sharingCheck A 32-byte value used to verify that all IKeymasterDevice instances have
      *         computed the same shared HMAC key.  The sharingCheck value is computed as follows:
      *
      *             sharingCheck = HMAC(H, "Keymaster HMAC Verification")
      *
-     *         The string is UTF-8 encoded.  If the returned values of all Keymaster instances don't
-     *         match, Keystore will assume that HMAC agreement failed.
+     *         The string is UTF-8 encoded, 27 bytes in length.  If the returned values of all
+     *         IKeymasterDevice instances don't match, Keystore will assume that HMAC agreement
+     *         failed.
      */
     computeSharedHmac(vec<HmacSharingParameters> params)
         generates (ErrorCode error, vec<uint8_t> sharingCheck);
 
     /**
-     * Verify authorizations for another Keymaster instance.
+     * Verify authorizations for another IKeymasterDevice instance.
      *
-     * On systems with both a StrongBox and a TEE Keymaster instance it is sometimes useful to ask
-     * the TEE Keymaster to verify authorizations for a key hosted in StrongBox.
+     * On systems with both a StrongBox and a TEE IKeymasterDevice instance it is sometimes useful
+     * to ask the TEE IKeymasterDevice to verify authorizations for a key hosted in StrongBox.
      *
      * For every StrongBox operation, Keystore is required to call this method on the TEE Keymaster,
      * passing in the StrongBox key's hardwareEnforced authorization list and the operation handle
-     * returned by StrongBox begin().  The TEE Keymaster must validate all of the authorizations it
-     * can and return those it validated in the VerificationToken.  If it cannot verify any, the
-     * parametersVerified field of the VerificationToken must be empty.  Keystore must then pass the
-     * VerificationToken to the subsequent invocations of StrongBox update() and finish().
+     * returned by StrongBox begin().  The TEE IKeymasterDevice must validate all of the
+     * authorizations it can and return those it validated in the VerificationToken.  If it cannot
+     * verify any, the parametersVerified field of the VerificationToken must be empty.  Keystore
+     * must then pass the VerificationToken to the subsequent invocations of StrongBox update() and
+     * finish().
      *
      * StrongBox implementations must return ErrorCode::UNIMPLEMENTED.
      *
      * @param operationHandle the operation handle returned by StrongBox Keymaster's begin().
      *
-     * @param parametersToVerify Set of authorizations to verify.
+     * @param parametersToVerify Set of authorizations to verify.  The caller may provide an empty
+     *        vector if the only required information is the TEE timestamp.
      *
      * @param authToken A HardwareAuthToken if needed to authorize key usage.
+     *
+     * @return error ErrorCode::OK on success or ErrorCode::UNIMPLEMENTED if the IKeymasterDevice is
+     *         a StrongBox.  If the IKeymasterDevice cannot verify one or more elements of
+     *         parametersToVerify it must not return an error code, but just omit the unverified
+     *         parameter from the VerificationToken.
+     *
+     * @return token the verification token.  See VerificationToken in types.hal for details.
      */
     verifyAuthorization(uint64_t operationHandle, vec<KeyParameter> parametersToVerify,
                         HardwareAuthToken authToken)
@@ -162,53 +366,143 @@
 
 
     /**
-     * Adds entropy to the RNG used by Keymaster.  Entropy added through this method is guaranteed
-     * not to be the only source of entropy used, and the mixing function is required to be secure,
-     * in the sense that if the RNG is seeded (from any source) with any data the attacker cannot
-     * predict (or control), then the RNG output is indistinguishable from random.  Thus, if the
-     * entropy from any source is good, the output must be good.
+     * Adds entropy to the RNG used by Keymaster.  Entropy added through this method must not be the
+     * only source of entropy used, and a secure mixing function must be used to mix the entropy
+     * provided by this method with internally-generated entropy.  The mixing function must be
+     * secure in the sense that if any one of the mixing function inputs is provided with any data
+     * the attacker cannot predict (or control), then the output of the seeded CRNG is
+     * indistinguishable from random.  Thus, if the entropy from any source is good, the output must
+     * be good.
      *
-     * @param data Bytes to be mixed into the RNG.
+     * @param data Bytes to be mixed into the CRNG seed.  The caller must not provide more than 2
+     *        KiB of data per invocation.
      *
-     * @return error See the ErrorCode enum in types.hal.
+     * @return error ErrorCode::OK on success; ErrorCode::INVALID_INPUT_LENGTH if the caller
+     *         provides more than 2 KiB of data.
      */
     addRngEntropy(vec<uint8_t> data) generates (ErrorCode error);
 
     /**
-     * Generates a key, or key pair, returning a key blob and a description of the key.
+     * Generates a new cryptographic key, specifying associated parameters, which must be
+     * cryptographically bound to the key.  IKeymasterDevice implementations must disallow any use
+     * of a key in any way inconsistent with the authorizations specified at generation time.  With
+     * respect to parameters that the secure environment cannot enforce, the secure envionment's
+     * obligation is limited to ensuring that the unenforceable parameters associated with the key
+     * cannot be modified, so that every call to getKeyCharacteristics returns the original
+     * values.  In addition, the characteristics returned by generateKey places parameters correctly
+     * in the hardware-enforced and software-enforced lists.  See getKeyCharacteristics for more
+     * details.
      *
-     * @param keyParams Key generation parameters are defined as Keymaster tag/value pairs, provided
-     *        in params.  See Tag in types.hal for the full list.
+     * In addition to the parameters provided, generateKey must add the following to the returned
+     * characteristics.
      *
-     * @return error See the ErrorCode enum in types.hal.
+     * o Tag::ORIGIN with the value KeyOrigin::GENERATED.
      *
-     * @return keyBlob Opaque, encrypted descriptor of the generated key.  A recommended
-     *        implementation strategy is to include an encrypted copy of the key material, wrapped
-     *        in a key unavailable outside secure hardware.
+     * o Tag::BLOB_USAGE_REQUIREMENTS with the appropriate value (see KeyBlobUsageRequirements in
+     *   types.hal).
      *
-     * @return keyCharacteristics Description of the generated key.  See KeyCharacteristis in
-     *         types.hal.
+     * o Tag::CREATION_DATETIME with the appropriate value.  Note that it is expected that this will
+     *   generally be added by the HAL, not by the secure environment, and that it will be in the
+     *   software-enforced list.  It must be cryptographically bound to the key, like all tags.
+     *
+     * o Tag::OS_VERSION, Tag::OS_PATCHLEVEL, Tag::VENDOR_PATCHLEVEL and Tag::BOOT_PATCHLEVEL with
+     *   appropriate values.
+     *
+     * The parameters provided to generateKey depend on the type of key being generated.  This
+     * section summarizes the necessary and optional tags for each type of key.  Tag::ALGORITHM is
+     * always necessary, to specify the type.
+     *
+     * == RSA Keys ==
+     *
+     * The following parameters are required to generate an RSA key:
+     *
+     * o Tag::Key_SIZE specifies the size of the public modulus, in bits.  If omitted, generateKey
+     *   must return ErrorCode::UNSUPPORTED_KEY_SIZE.  Required values for TEE IKeymasterDevice
+     *   implementations are 1024, 2048, 3072 and 4096.  StrongBox IKeymasterDevice implementations
+     *   must support 2048.
+     *
+     * o Tag::RSA_PUBLIC_EXPONENT specifies the RSA public exponent value.  If omitted, generateKey
+     *   must return ErrorCode::INVALID_ARGUMENT.  The values 3 and 65537 must be supported.  It is
+     *   recommended to support all prime values up to 2^64.  If provided with a non-prime value,
+     *   generateKey must return ErrorCode::INVALID_ARGUMENT.
+     *
+     * The following parameters are not necessary to generate a usable RSA key, but generateKey must
+     * not return an error if they are omitted:
+     *
+     * o Tag::PURPOSE specifies allowed purposes.  All KeyPurpose values (see types.hal) must be
+     *   supported for RSA keys.
+     *
+     * o Tag::DIGEST specifies digest algorithms that may be used with the new key.  TEE
+     *   IKeymasterDevice implementatiosn must support all Digest values (see types.hal) for RSA
+     *   keys.  StrongBox IKeymasterDevice implementations must support SHA_2_256.
+     *
+     * o Tag::PADDING specifies the padding modes that may be used with the new
+     *   key.  IKeymasterDevice implementations must support PaddingMode::NONE,
+     *   PaddingMode::RSA_OAEP, PaddingMode::RSA_PSS, PaddingMode::RSA_PKCS1_1_5_ENCRYPT and
+     *   PaddingMode::RSA_PKCS1_1_5_SIGN for RSA keys.
+     *
+     * == ECDSA Keys ==
+     *
+     * Either Tag::KEY_SIZE or Tag::EC_CURVE must be provided to generate an ECDSA key.  If neither
+     * is provided, generateKey must return ErrorCode::UNSUPPORTED_KEY_SIZE.  If Tag::KEY_SIZE is
+     * provided, the possible values are 224, 256, 384 and 521, and must be mapped to Tag::EC_CURVE
+     * values P_224, P_256, P_384 and P_521, respectively.  TEE IKeymasterDevice implementations
+     * must support all curves.  StrongBox implementations must support P_256.
+     *
+     * == AES Keys ==
+     *
+     * Only Tag::KEY_SIZE is required to generate an AES key.  If omitted, generateKey must return
+     * ErrorCode::UNSUPPORTED_KEY_SIZE.  128 and 256-bit key sizes must be supported.
+     *
+     * If Tag::BLOCK_MODE is specified with value BlockMode::GCM, then the caller must also provide
+     * Tag::MIN_MAC_LENGTH.  If omitted, generateKey must return ErrorCode::MISSING_MIN_MAC_LENGTH.
+     *
+     *
+     * @param keyParams Key generation parameters are defined as IKeymasterDevice tag/value pairs,
+     *        provided in params.  See above for detailed specifications of which tags are required
+     *        for which types of keys.
+     *
+     * @return keyBlob Opaque descriptor of the generated key.  The recommended implementation
+     *         strategy is to include an encrypted copy of the key material, wrapped in a key
+     *         unavailable outside secure hardware.
+     *
+     * @return keyCharacteristics Description of the generated key.  See the getKeyCharacteristics
+     *         method below.
      */
     generateKey(vec<KeyParameter> keyParams)
         generates (ErrorCode error, vec<uint8_t> keyBlob, KeyCharacteristics keyCharacteristics);
 
     /**
-     * Imports a key, or key pair, returning a key blob and/or a description of the key.
+     * Imports key material into an IKeymasterDevice.  Key definition parameters and return values
+     * are the same as for generateKey, with the following exceptions:
      *
-     * @param keyParams Key generation parameters are defined as Keymaster tag/value pairs, provided
-     *        in params.  See Tag for the full list.
+     * o Tag::KEY_SIZE is not necessary in the input parameters.  If not provided, the
+     *   IKeymasterDevice must deduce the value from the provided key material and add the tag and
+     *   value to the key characteristics.  If Tag::KEY_SIZE is provided, the IKeymasterDevice must
+     *   validate it against the key material.  In the event of a mismatch, importKey must return
+     *   ErrorCode::IMPORT_PARAMETER_MISMATCH.
      *
-     * @param keyFormat The format of the key material to import.
+     * o Tag::RSA_PUBLIC_EXPONENT (for RSA keys only) is not necessary in the input parameters.  If
+     *   not provided, the IKeymasterDevice must deduce the value from the provided key material and
+     *   add the tag and value to the key characteristics.  If Tag::RSA_PUBLIC_EXPONENT is provided,
+     *   the IKeymasterDevice must validate it against the key material.  In the event of a
+     *   mismatch, importKey must return ErrorCode::IMPORT_PARAMETER_MISMATCH.
+     *
+     * o Tag::ORIGIN (returned in keyCharacteristics) must have the value KeyOrigin::IMPORTED.
+     *
+     * @param keyParams Key generation parameters are defined as IKeymasterDevice tag/value pairs,
+     *        provided in params.
+     *
+     * @param keyFormat The format of the key material to import.  See KeyFormat in types.hal.
      *
      * @pram keyData The key material to import, in the format specifed in keyFormat.
      *
-     * @return error See the ErrorCode enum.
+     * @return keyBlob Opaque descriptor of the imported key.  The recommended implementation
+     *         strategy is to include an encrypted copy of the key material, wrapped in a key
+     *         unavailable outside secure hardware.
      *
-     * @return keyBlob Opaque, encrypted descriptor of the generated key, which will generally
-     *         contain a copy of the key material, wrapped in a key unavailable outside secure
-     *         hardware.
-     *
-     * @return keyCharacteristics Decription of the generated key.
+     * @return keyCharacteristics Decription of the generated key.  See the getKeyCharacteristics
+     *         method below.
      */
     importKey(vec<KeyParameter> keyParams, KeyFormat keyFormat, vec<uint8_t> keyData)
         generates (ErrorCode error, vec<uint8_t> keyBlob, KeyCharacteristics keyCharacteristics);
@@ -241,10 +535,10 @@
      *     o keyParams is the characteristics of the key to be imported (as with generateKey or
      *       importKey).  If the secure import is successful, these characteristics must be
      *       associated with the key exactly as if the key material had been insecurely imported
-     *       with the @3.0::IKeymasterDevice::importKey.
+     *       with the @3.0::IKeymasterDevice::importKey.  See attestKey() for documentation of the
+     *       AuthorizationList schema.
      *     o encryptedTransportKey is a 256-bit AES key, XORed with a masking key and then encrypted
-     *       in RSA-OAEP mode (SHA-256 digest, SHA-1 MGF1 digest) with the wrapping key specified by
-     *       wrappingKeyBlob.
+     *       with the wrapping key specified by wrappingKeyBlob.
      *     o keyDescription is a KeyDescription, above.
      *     o encryptedKey is the key material of the key to be imported, in format keyFormat, and
      *       encrypted with encryptedEphemeralKey in AES-GCM mode, with the DER-encoded
@@ -266,10 +560,7 @@
      *        that the origin tag should be set to SECURELY_IMPORTED.
      *
      * @param wrappingKeyBlob The opaque key descriptor returned by generateKey() or importKey().
-     *        This key must have been created with Purpose::WRAP_KEY, and must be a key algorithm
-     *        that supports encryption and must be at least as strong (in key size) as the key to be
-     *        imported (per NIST key length recommendations: 112 bits symmetric is equivalent to
-     *        2048-bit RSA or 224-bit EC, 128 bits symmetric ~ 3072-bit RSA or 256-bit EC, etc.).
+     *        This key must have been created with Purpose::WRAP_KEY.
      *
      * @param maskingKey The 32-byte value XOR'd with the transport key in the SecureWrappedKey
      *        structure.
@@ -291,8 +582,6 @@
      *        If the wrappedKeyData does not contain such a tag and value, this argument must be
      *        ignored.
      *
-     * @return error See the ErrorCode enum.
-     *
      * @return keyBlob Opaque descriptor of the imported key.  It is recommended that the keyBlob
      *         contain a copy of the key material, wrapped in a key unavailable outside secure
      *         hardware.
@@ -303,10 +592,18 @@
         generates(ErrorCode error, vec<uint8_t> keyBlob, KeyCharacteristics keyCharacteristics);
 
     /**
-     * Returns the characteristics of the specified key, if the keyBlob is valid (implementations
-     * must fully validate the integrity of the key).
+     * Returns parameters associated with the provided key, divided into two sets: hardware-enforced
+     * and software-enforced.  The description here applies equally to the key characteristics lists
+     * returned by generateKey, importKey and importWrappedKey.  The characteristics returned by
+     * this method completely describe the type and usage of the specified key.
      *
-     * @param keyBlob The opaque descriptor returned by generateKey() or importKey();
+     * The rule that IKeymasterDevice implementations must use for deciding whether a given tag
+     * belongs in the hardware-enforced or software-enforced list is that if the meaning of the tag
+     * is fully assured by secure hardware, it is hardware enforced.  Otherwise, it's software
+     * enforced.
+     *
+     *
+     * @param keyBlob The opaque descriptor returned by generateKey, importKey or importWrappedKey.
      *
      * @param clientId An opaque byte string identifying the client.  This value must match the
      *        Tag::APPLICATION_ID data provided during key generation/import.  Without the correct
@@ -318,9 +615,7 @@
      *        value, it must be computationally infeasible for the secure hardware to obtain the key
      *        material.
      *
-     * @return error See the ErrorCode enum in types.hal.
-     *
-     * @return keyCharacteristics Decription of the generated key.  See KeyCharacteristis in
+     * @return keyCharacteristics Decription of the generated key.  See KeyCharacteristics in
      *         types.hal.
      */
     getKeyCharacteristics(vec<uint8_t> keyBlob, vec<uint8_t> clientId, vec<uint8_t> appData)
@@ -344,8 +639,6 @@
      *        value, it must be computationally infeasible for the secure hardware to obtain the key
      *        material.
      *
-     * @return error See the ErrorCode enum in types.hal.
-     *
      * @return keyMaterial The public key material in PKCS#8 format.
      */
     exportKey(KeyFormat keyFormat, vec<uint8_t> keyBlob, vec<uint8_t> clientId,
@@ -353,56 +646,191 @@
 
     /**
      * Generates a signed X.509 certificate chain attesting to the presence of keyToAttest in
-     * Keymaster.  The certificate must contain an extension with OID 1.3.6.1.4.1.11129.2.1.17 and
-     * value defined in:
+     * Keymaster.
      *
-     *     https://developer.android.com/training/articles/security-key-attestation.html.
+     * The certificates in the chain must be ordered such that each certificate is signed by the
+     * subsequent one, up to the root which must be self-signed.  The first certificate in the chain
+     * signs the public key info of the attested key and must contain the following entries (see RFC
+     * 5280 for details on each):
+     *
+     * o version -- with value 2
+     *
+     * o serialNumber -- with value 1 (same value for all keys)
+     *
+     * o signature -- contains an the AlgorithmIdentifier of the algorithm used to sign, must be
+     *   ECDSA for EC keys, RSA for RSA keys.
+     *
+     * o issuer -- must contain the same value as the Subject field of the next certificate.
+     *
+     * o validity -- SEQUENCE of two dates, containing the values of Tag::ACTIVE_DATETIME and
+     *   Tag::USAGE_EXPIRE_DATETIME.  The tag values are in milliseconds since Jan 1, 1970; see RFD
+     *   5280 for the correct representation in certificates.  If Tag::ACTIVE_DATETIME is not
+     *   present in the key, the IKeymasterDevice must use the value of Tag::CREATION_DATETIME.  If
+     *   Tag::USAGE_EXPIRE_DATETIME is not present, the IKeymasterDevice must use the expiration
+     *   date of the batch attestation certificate (see below).
+     *
+     * o subject -- CN="Android Keystore Key" (same value for all keys)
+     *
+     * o subjectPublicKeyInfo -- X.509 SubjectPublicKeyInfo containing the attested public key.
+     *
+     * o Key Usage extension -- digitalSignature bit must be set iff the attested key has
+     *   KeyPurpose::SIGN.  dataEncipherment bit must be set iff the attested key has
+     *   KeyPurpose::DECRYPT.  keyEncipherment bit must be set iff the attested key has
+     *   KeyPurpose::KEY_WRAP.  All other bits must be clear.
+     *
+     * In addition to the above, the attestation certificate must contain an extension with OID
+     * 1.3.6.1.4.1.11129.2.1.17 and value according to the KeyDescription schema defined as:
+     *
+     * KeyDescription ::= SEQUENCE {
+     *     attestationVersion         INTEGER, # Value 3
+     *     attestationSecurityLevel   SecurityLevel, # See below
+     *     keymasterVersion           INTEGER, # Value 4
+     *     keymasterSecurityLevel     SecurityLevel, # See below
+     *     attestationChallenge       OCTET_STRING, # Tag::ATTESTATION_CHALLENGE from attestParams
+     *     uniqueId                   OCTET_STRING, # Empty unless key has Tag::INCLUDE_UNIQUE_ID
+     *     softwareEnforced           AuthorizationList, # See below
+     *     hardwareEnforced           AuthorizationList, # See below
+     * }
+     *
+     * SecurityLevel ::= ENUMERATED {
+     *     Software                   (0),
+     *     TrustedEnvironment         (1),
+     *     StrongBox                  (2),
+     * }
+     *
+     * RootOfTrust ::= SEQUENCE {
+     *     verifiedBootKey            OCTET_STRING,
+     *     deviceLocked               BOOLEAN,
+     *     verifiedBootState          VerifiedBootState,
+     *     # verifiedBootHash must contain 32-byte value that represents the state of all binaries
+     *     # or other components validated by verified boot.  Updating any verified binary or
+     *     # component must cause this value to change.
+     *     verifiedBootHash           OCTET_STRING,
+     * }
+     *
+     * VerifiedBootState ::= ENUMERATED {
+     *     Verified                   (0),
+     *     SelfSigned                 (1),
+     *     Unverified                 (2),
+     *     Failed                     (3),
+     * }
+     *
+     * AuthorizationList ::= SEQUENCE {
+     *     purpose                    [1] EXPLICIT SET OF INTEGER OPTIONAL,
+     *     algorithm                  [2] EXPLICIT INTEGER OPTIONAL,
+     *     keySize                    [3] EXPLICIT INTEGER OPTIONAL.
+     *     blockMode                  [4] EXPLICIT SET OF INTEGER OPTIONAL,
+     *     digest                     [5] EXPLICIT SET OF INTEGER OPTIONAL,
+     *     padding                    [6] EXPLICIT SET OF INTEGER OPTIONAL,
+     *     ecCurve                    [10] EXPLICIT INTEGER OPTIONAL,
+     *     rsaPublicExponent          [200] EXPLICIT INTEGER OPTIONAL,
+     *     rollbackResistance         [303] EXPLICIT NULL OPTIONAL,
+     *     activeDateTime             [400] EXPLICIT INTEGER OPTIONAL
+     *     originationExpireDateTime  [401] EXPLICIT INTEGER OPTIONAL
+     *     usageExpireDateTime        [402] EXPLICIT INTEGER OPTIONAL
+     *     noAuthRequired             [503] EXPLICIT NULL OPTIONAL,
+     *     userAuthType               [504] EXPLICIT INTEGER OPTIONAL,
+     *     authTimeout                [505] EXPLICIT INTEGER OPTIONAL,
+     *     allowWhileOnBody           [506] EXPLICIT NULL OPTIONAL,
+     *     trustedUserPresenceReq     [507] EXPLICIT NULL OPTIONAL,
+     *     trustedConfirmationReq     [508] EXPLICIT NULL OPTIONAL,
+     *     unlockedDeviceReq          [509] EXPLICIT NULL OPTIONAL,
+     *     allApplications            [600] EXPLICIT NULL OPTIONAL,
+     *     applicationId              [601] EXPLICIT OCTET_STRING OPTIONAL,
+     *     creationDateTime           [701] EXPLICIT INTEGER OPTIONAL,
+     *     origin                     [702] EXPLICIT INTEGER OPTIONAL,
+     *     rollbackResistant          [703] EXPLICIT NULL OPTIONAL,
+     *     rootOfTrust                [704] EXPLICIT RootOfTrust OPTIONAL,
+     *     osVersion                  [705] EXPLICIT INTEGER OPTIONAL,
+     *     osPatchLevel               [706] EXPLICIT INTEGER OPTIONAL,
+     *     attestationChallenge       [708] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationApplicationId   [709] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationIdBrand         [710] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationIdDevice        [711] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationIdProduct       [712] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationIdSerial        [713] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationIdImei          [714] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationIdMeid          [715] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationIdManufacturer  [716] EXPLICIT OCTET_STRING OPTIONAL,
+     *     attestationIdModel         [717] EXPLICIT OCTET_STRING OPTIONAL,
+     *     vendorPatchLevel           [718] EXPLICIT INTEGER OPTIONAL,
+     *     bootPatchLevel             [718] EXPLICIT INTEGER OPTIONAL,
+     * }
+     *
+     * The above schema is mostly a straightforward translation of the IKeymasterDevice tag/value
+     * parameter lists to ASN.1:
+     *
+     * o TagType::ENUM, TagType::UINT, TagType::ULONG and TagType::DATE tags are represented as
+     *   ASN.1 INTEGER.
+     *
+     * o TagType::ENUM_REP, TagType::UINT_REP and TagType::ULONG_REP tags are represented as ASN.1
+     *   SET of INTEGER.
+     *
+     * o TagType::BOOL tags are represented as ASN.1 NULL.  All entries in AuthorizationList are
+     *   OPTIONAL, so the presence of the tag means "true", absence means "false".
+     *
+     * o TagType::BYTES tags are represented as ASN.1 OCTET_STRING.
+     *
+     * The numeric ASN.1 tag numbers are the same values as the IKeymasterDevice Tag enum values,
+     * except with the TagType modifier stripped.
+     *
+     * The attestation certificate must be signed by a "batch" key, which must be securely
+     * pre-installed into the device, generally in the factory, and securely stored to prevent
+     * access or extraction.  The batch key must be used only for signing attestation certificates.
+     * The batch attestation certificate must be signed by a chain or zero or more intermediates
+     * leading to a self-signed roots.  The intermediate and root certificate signing keys must not
+     * exist anywhere on the device.
+     *
+     * == ID Attestation ==
+     *
+     * ID attestation is a special case of key attestation in which unique device ID values are
+     * included in the signed attestation certificate.
      *
      * @param keyToAttest The opaque descriptor returned by generateKey() or importKey().  The
      *        referenced key must be asymmetric.
      *
-     * @param attestParams Parameters for the attestation, notably Tag::ATTESTATION_CHALLENGE.
-     *
-     * @return error See the ErrorCode enum in types.hal.
+     * @param attestParams Parameters for the attestation.  Must contain Tag::ATTESTATION_CHALLENGE,
+     *        the value of which must be put in the attestationChallenge field of the KeyDescription
+     *        ASN.1 structure defined above.
      *
      * @return certChain The attestation certificate, and additional certificates back to the root
      *         attestation certificate, which clients will need to check against a known-good value.
+     *         The certificates must be DER-encoded.
      */
     attestKey(vec<uint8_t> keyToAttest, vec<KeyParameter> attestParams)
         generates (ErrorCode error, vec<vec<uint8_t>> certChain);
 
     /**
-     * Upgrades an old key blob.  Keys can become "old" in two ways: Keymaster can be upgraded to a
-     * new version with an incompatible key blob format, or the system can be updated to invalidate
-     * the OS version (OS_VERSION tag), system patch level (OS_PATCHLEVEL tag), vendor patch level
-     * (VENDOR_PATCH_LEVEL tag), boot patch level (BOOT_PATCH_LEVEL tag) or other,
+     * Upgrades an old key blob.  Keys can become "old" in two ways: IKeymasterDevice can be
+     * upgraded to a new version with an incompatible key blob format, or the system can be updated
+     * to invalidate the OS version (OS_VERSION tag), system patch level (OS_PATCHLEVEL tag), vendor
+     * patch level (VENDOR_PATCH_LEVEL tag), boot patch level (BOOT_PATCH_LEVEL tag) or other,
      * implementation-defined patch level (keymaster implementers are encouraged to extend this HAL
-     * with a minor version extension to define validatable patch levels for other images; tags
-     * must be defined in the implemeter's namespace, starting at 10000).  In either case,
-     * attempts to use an old key blob with getKeyCharacteristics(), exportKey(), attestKey() or
-     * begin() must result in Keymaster returning ErrorCode::KEY_REQUIRES_UPGRADE.  The caller must
-     * use this method to upgrade the key blob.
+     * with a minor version extension to define validatable patch levels for other images; tags must
+     * be defined in the implementer's namespace, starting at 10000).  In either case, attempts to
+     * use an old key blob with getKeyCharacteristics(), exportKey(), attestKey() or begin() must
+     * result in IKeymasterDevice returning ErrorCode::KEY_REQUIRES_UPGRADE.  The caller must use
+     * this method to upgrade the key blob.
      *
-     * If upgradeKey is asked to update a key with any version or patch level that is higher than
-     * the current system version or patch level, it must return ErrorCode::INVALID_ARGUMENT.  There
-     * is one exception: it is always permissible to "upgrade" from any OS_VERSION number to
-     * OS_VERSION 0.  For example, if the key has OS_VERSION 080001, it is permisible to upgrade the
-     * key if the current system version is 080100, because the new version is larger, or if the
-     * current system version is 0, because upgrades to 0 are always allowed.  If the system version
-     * were 080000, however, keymaster must return ErrorCode::INVALID_ARGUMENT because that value is
-     * smaller than 080001.
+     * The upgradeKey method must examine each version or patch level associated with the key.  If
+     * any one of them is higher than the corresponding current device value upgradeKey() must
+     * return ErrorCode::INVALID_ARGUMENT.  There is one exception: it is always permissible to
+     * "downgrade" from any OS_VERSION number to OS_VERSION 0.  For example, if the key has
+     * OS_VERSION 080001, it is permisible to upgrade the key if the current system version is
+     * 080100, because the new version is larger, or if the current system version is 0, because
+     * upgrades to 0 are always allowed.  If the system version were 080000, however, keymaster must
+     * return ErrorCode::INVALID_ARGUMENT because that value is smaller than 080001.  Values other
+     * than OS_VERSION must never be downgraded.
      *
      * Note that Keymaster versions 2 and 3 required that the system and boot images have the same
-     * patch level and OS version.  This requirement is relaxed for Keymaster 4, and the OS version
-     * in the boot image footer is no longer used.
+     * patch level and OS version.  This requirement is relaxed for 4.0::IKeymasterDevice, and the
+     * OS version in the boot image footer is no longer used.
      *
      * @param keyBlobToUpgrade The opaque descriptor returned by generateKey() or importKey();
      *
      * @param upgradeParams A parameter list containing any parameters needed to complete the
      *        upgrade, including Tag::APPLICATION_ID and Tag::APPLICATION_DATA.
      *
-     * @return error See the ErrorCode enum.
-     *
      * @return upgradedKeyBlob A new key blob that references the same key as keyBlobToUpgrade, but
      *         is in the new format, or has the new version data.
      */
@@ -416,8 +844,6 @@
      * unusable.
      *
      * @param keyBlob The opaque descriptor returned by generateKey() or importKey();
-     *
-     * @return error See the ErrorCode enum.
      */
     deleteKey(vec<uint8_t> keyBlob) generates (ErrorCode error);
 
@@ -441,8 +867,6 @@
      * must never attest any device ids.
      *
      * This is a NOP if device id attestation is not supported.
-     *
-     * @return error See the ErrorCode enum.
      */
     destroyAttestationIds() generates (ErrorCode error);
 
@@ -452,12 +876,180 @@
      * to update(), finish() or abort().
      *
      * It is critical that each call to begin() be paired with a subsequent call to finish() or
-     * abort(), to allow the Keymaster implementation to clean up any internal operation state.  The
-     * caller's failure to do this may leak internal state space or other internal resources and may
-     * eventually cause begin() to return ErrorCode::TOO_MANY_OPERATIONS when it runs out of space
-     * for operations.  Any result other than ErrorCode::OK from begin(), update() or finish()
-     * implicitly aborts the operation, in which case abort() need not be called (and must return
-     * ErrorCode::INVALID_OPERATION_HANDLE if called).
+     * abort(), to allow the IKeymasterDevice implementation to clean up any internal operation
+     * state.  The caller's failure to do this may leak internal state space or other internal
+     * resources and may eventually cause begin() to return ErrorCode::TOO_MANY_OPERATIONS when it
+     * runs out of space for operations.  Any result other than ErrorCode::OK from begin(), update()
+     * or finish() implicitly aborts the operation, in which case abort() need not be called (and
+     * must return ErrorCode::INVALID_OPERATION_HANDLE if called).  IKeymasterDevice implementations
+     * must support 16 concurrent operations.
+     *
+     * If Tag::APPLICATION_ID or Tag::APPLICATION_DATA were specified during key generation or
+     * import, calls to begin must include those tags with the originally-specified values in the
+     * inParams argument to this method.  If not, begin() must return ErrorCode::INVALID_KEY_BLOB.
+     *
+     * == Authorization Enforcement ==
+     *
+     * The following key authorization parameters must be enforced by the IKeymasterDevice secure
+     * environment if the tags were returned in the "hardwareEnforced" list in the
+     * KeyCharacteristics.  Public key operations, meaning KeyPurpose::ENCRYPT and
+     * KeyPurpose::VERIFY must be allowed to succeed even if authorization requirements are not met.
+     *
+     * -- All Key Types --
+     *
+     * The tags in this section apply to all key types.  See below for additional key type-specific
+     * tags.
+     *
+     * o Tag::PURPOSE: The purpose specified in the begin() call must match one of the purposes in
+     *   the key authorizations.  If the specified purpose does not match, begin() must return
+     *   ErrorCode::UNSUPPORTED_PURPOSE.
+     *
+     * o Tag::ACTIVE_DATETIME can only be enforced if a trusted UTC time source is available.  If
+     *   the current date and time is prior to the tag value, begin() must return
+     *   ErrorCode::KEY_NOT_YET_VALID.
+     *
+     * o Tag::ORIGINATION_EXPIRE_DATETIME can only be enforced if a trusted UTC time source is
+     *   available.  If the current date and time is later than the tag value and the purpose is
+     *   KeyPurpose::ENCRYPT or KeyPurpose::SIGN, begin() must return ErrorCode::KEY_EXPIRED.
+     *
+     * o Tag::USAGE_EXPIRE_DATETIME can only be enforced if a trusted UTC time source is
+     *   available.  If the current date and time is later than the tag value and the purpose is
+     *   KeyPurpose::DECRYPT or KeyPurpose::VERIFY, begin() must return ErrorCode::KEY_EXPIRED.
+
+     * o Tag::MIN_SECONDS_BETWEEN_OPS must be compared with a trusted relative timer indicating the
+     *   last use of the key.  If the last use time plus the tag value is less than the current
+     *   time, begin() must return ErrorCode::KEY_RATE_LIMIT_EXCEEDED.  See the tag description for
+     *   important implementation details.
+
+     * o Tag::MAX_USES_PER_BOOT must be compared against a secure counter that tracks the uses of
+     *   the key since boot time.  If the count of previous uses exceeds the tag value, begin() must
+     *   return ErrorCode::KEY_MAX_OPS_EXCEEDED.
+     *
+     * o Tag::USER_SECURE_ID must be enforced by this method if and only if the key also has
+     *   Tag::AUTH_TIMEOUT (if it does not have Tag::AUTH_TIMEOUT, the Tag::USER_SECURE_ID
+     *   requirement must be enforced by update() and finish()).  If the key has both, then this
+     *   method must receive a non-empty HardwareAuthToken in the authToken argument.  For the auth
+     *   token to be valid, all of the following have to be true:
+     *
+     *   o The HMAC field must validate correctly.
+     *
+     *   o At least one of the Tag::USER_SECURE_ID values from the key must match at least one of
+     *     the secure ID values in the token.
+     *
+     *   o The key must have a Tag::USER_AUTH_TYPE that matches the auth type in the token.
+     *
+     *   o The timestamp in the auth token plus the value of the Tag::AUTH_TIMEOUT must be less than
+     *     the current secure timestamp (which is a monotonic timer counting milliseconds since
+     *     boot.)
+     *
+     *   If any of these conditions are not met, begin() must return
+     *   ErrorCode::KEY_USER_NOT_AUTHENTICATED.
+     *
+     * o Tag::CALLER_NONCE allows the caller to specify a nonce or initialization vector (IV).  If
+     *   the key doesn't have this tag, but the caller provided Tag::NONCE to this method,
+     *   ErrorCode::CALLER_NONCE_PROHIBITED must be returned.
+     *
+     * o Tag::BOOTLOADER_ONLY specifies that only the bootloader may use the key.  If this method is
+     *   called with a bootloader-only key after the bootloader has finished executing, it must
+     *   return ErrorCode::INVALID_KEY_BLOB.  The mechanism for notifying the IKeymasterDevice that
+     *   the bootloader has finished executing is implementation-defined.
+     *
+     * -- RSA Keys --
+     *
+     * All RSA key operations must specify exactly one padding mode in inParams.  If unspecified or
+     * specified more than once, the begin() must return ErrorCode::UNSUPPORTED_PADDING_MODE.
+     *
+     * RSA signing and verification operations need a digest, as do RSA encryption and decryption
+     * operations with OAEP padding mode.  For those cases, the caller must specify exactly one
+     * digest in inParams.  If unspecified or specified more than once, begin() must return
+     * ErrorCode::UNSUPPORTED_DIGEST.
+     *
+     * Private key operations (KeyPurpose::DECRYPT and KeyPurpose::SIGN) need authorization of
+     * digest and padding, which means that the key authorizations need to contain the specified
+     * values.  If not, begin() must return ErrorCode::INCOMPATIBLE_DIGEST or
+     * ErrorCode::INCOMPATIBLE_PADDING, as appropriate.  Public key operations (KeyPurpose::ENCRYPT
+     * and KeyPurpose::VERIFY) are permitted with unauthorized digest or padding modes.
+     *
+     * With the exception of PaddingMode::NONE, all RSA padding modes are applicable only to certain
+     * purposes.  Specifically, PaddingMode::RSA_PKCS1_1_5_SIGN and PaddingMode::RSA_PSS only
+     * support signing and verification, while PaddingMode::RSA_PKCS1_1_5_ENCRYPT and
+     * PaddingMode::RSA_OAEP only support encryption and decryption.  begin() must return
+     * ErrorCode::UNSUPPORTED_PADDING_MODE if the specified mode does not support the specified
+     * purpose.
+     *
+     * There are some important interactions between padding modes and digests:
+     *
+     * o PaddingMode::NONE indicates that a "raw" RSA operation is performed.  If signing or
+     *   verifying, Digest::NONE is specified for the digest.  No digest is necessary for unpadded
+     *   encryption or decryption.
+     *
+     * o PaddingMode::RSA_PKCS1_1_5_SIGN padding requires a digest.  The digest may be Digest::NONE,
+     *   in which case the Keymaster implementation cannot build a proper PKCS#1 v1.5 signature
+     *   structure, because it cannot add the DigestInfo structure.  Instead, the IKeymasterDevice
+     *   must construct 0x00 || 0x01 || PS || 0x00 || M, where M is the provided message and PS is a
+     *   random padding string at least eight bytes in length.  The size of the RSA key has to be at
+     *   least 11 bytes larger than the message, otherwise begin() must return
+     *   ErrorCode::INVALID_INPUT_LENGTH.
+     *
+     * o PaddingMode::RSA_PKCS1_1_1_5_ENCRYPT padding does not require a digest.
+     *
+     * o PaddingMode::RSA_PSS padding requires a digest, which may not be Digest::NONE.  If
+     *   Digest::NONE is specified, the begin() must return ErrorCode::INCOMPATIBLE_DIGEST.  In
+     *   addition, the size of the RSA key must be at least 2 + D bytes larger than the output size
+     *   of the digest, where D is the size of the digest, in bytes.  Otherwise begin() must
+     *   return ErrorCode::INCOMPATIBLE_DIGEST.  The salt size must be D.
+     *
+     * o PaddingMode::RSA_OAEP padding requires a digest, which may not be Digest::NONE.  If
+     *   Digest::NONE is specified, begin() must return ErrorCode::INCOMPATIBLE_DIGEST.  The OAEP
+     *   mask generation function must be MGF1 and the MGF1 digest must be SHA1, regardless of the
+     *   OAEP digest specified.
+     *
+     * -- EC Keys --
+     *
+     * EC key operations must specify exactly one padding mode in inParams.  If unspecified or
+     * specified more than once, begin() must return ErrorCode::UNSUPPORTED_PADDING_MODE.
+     *
+     * Private key operations (KeyPurpose::SIGN) need authorization of digest and padding, which
+     * means that the key authorizations must contain the specified values.  If not, begin() must
+     * return ErrorCode::INCOMPATIBLE_DIGEST.  Public key operations (KeyPurpose::VERIFY) are
+     * permitted with unauthorized digest or padding.
+     *
+     * -- AES Keys --
+     *
+     * AES key operations must specify exactly one block mode (Tag::BLOCK_MODE) and one padding mode
+     * (Tag::PADDING) in inParams.  If either value is unspecified or specified more than once,
+     * begin() must return ErrorCode::UNSUPPORTED_BLOCK_MODE or
+     * ErrorCode::UNSUPPORTED_PADDING_MODE.  The specified modes must be authorized by the key,
+     * otherwise begin() must return ErrorCode::INCOMPATIBLE_BLOCK_MODE or
+     * ErrorCode::INCOMPATIBLE_PADDING_MODE.
+     *
+     * If the block mode is BlockMode::GCM, inParams must specify Tag::MAC_LENGTH, and the specified
+     * value must be a multiple of 8 that is not greater than 128 or less than the value of
+     * Tag::MIN_MAC_LENGTH in the key authorizations.  For MAC lengths greater than 128 or
+     * non-multiples of 8, begin() must return ErrorCode::UNSUPPORTED_MAC_LENGTH.  For values less
+     * than the key's minimum length, begin() must return ErrorCode::INVALID_MAC_LENGTH.
+     *
+     * If the block mode is BlockMode::GCM or BlockMode::CTR, the specified padding mode must be
+     * PaddingMode::NONE.  For BlockMode::ECB or BlockMode::CBC, the mode may be PaddingMode::NONE
+     * or PaddingMode::PKCS7.  If the padding mode doesn't meet these conditions, begin() must
+     * return ErrorCode::INCOMPATIBLE_PADDING_MODE.
+     *
+     * If the block mode is BlockMode::CBC, BlockMode::CTR, or BlockMode::GCM, an initialization
+     * vector or nonce is required.  In most cases, callers shouldn't provide an IV or nonce and the
+     * IKeymasterDevice implementation must generate a random IV or nonce and return it via
+     * Tag::NONCE in outParams.  CBC and CTR IVs are 16 bytes.  GCM nonces are 12 bytes.  If the key
+     * authorizations contain Tag::CALLER_NONCE, then the caller may provide an IV/nonce with
+     * Tag::NONCE in inParams.  If a nonce is provided when Tag::CALLER_NONCE is not authorized,
+     * begin() must return ErrorCode::CALLER_NONCE_PROHIBITED.  If a nonce is not provided when
+     * Tag::CALLER_NONCE is authorized, IKeymasterDevice msut generate a random IV/nonce.
+     *
+     * -- HMAC keys --
+     *
+     * HMAC key operations must specify Tag::MAC_LENGTH in inParams.  The specified value must be a
+     * multiple of 8 that is not greater than the digest length or less than the value of
+     * Tag::MIN_MAC_LENGTH in the key authorizations.  For MAC lengths greater than the digest
+     * length or non-multiples of 8, begin() must return ErrorCode::UNSUPPORTED_MAC_LENGTH.  For
+     * values less than the key's minimum length, begin() must return ErrorCode::INVALID_MAC_LENGTH.
      *
      * @param purpose The purpose of the operation, one of KeyPurpose::ENCRYPT, KeyPurpose::DECRYPT,
      *        KeyPurpose::SIGN or KeyPurpose::VERIFY.  Note that for AEAD modes, encryption and
@@ -466,7 +1058,7 @@
      *
      * @param keyBlob The opaque key descriptor returned by generateKey() or importKey().  The key
      *        must have a purpose compatible with purpose and all of its usage requirements must be
-     *        satisfied, or begin() must return an appropriate error code.
+     *        satisfied, or begin() must return an appropriate error code (see above).
      *
      * @param inParams Additional parameters for the operation.  If Tag::APPLICATION_ID or
      *        Tag::APPLICATION_DATA were provided during generation, they must be provided here, or
@@ -478,8 +1070,6 @@
      * @param authToken Authentication token.  Callers that provide no token must set all numeric
      *        fields to zero and the MAC must be an empty vector.
      *
-     * @return error See the ErrorCode enum in types.hal.
-     *
      * @return outParams Output parameters.  Used to return additional data from the operation
      *         initialization, notably to return the IV or nonce from operations that generate an IV
      *         or nonce.
@@ -493,13 +1083,87 @@
 
     /**
      * Provides data to, and possibly receives output from, an ongoing cryptographic operation begun
-     * with begin().
+     * with begin().  The operation is specified by the operationHandle paramater.
      *
      * If operationHandle is invalid, update() must return ErrorCode::INVALID_OPERATION_HANDLE.
      *
-     * update() may not consume all of the data provided in the data buffer.  update() must return
-     * the amount consumed in inputConsumed.  The caller may provide the unconsumed data in a
-     * subsequent call.
+     * To provide more flexibility for buffer handling, implementations of this method have the
+     * option of consuming less data than was provided.  The caller is responsible for looping to
+     * feed the rest of the data in subsequent calls.  The amount of input consumed must be returned
+     * in the inputConsumed parameter.  Implementations must always consume at least one byte, unless
+     * the operation cannot accept any more; if more than zero bytes are provided and zero bytes are
+     * consumed, callers must consider this an error and abort the operation.
+     *
+     * Implementations may also choose how much data to return, as a result of the update.  This is
+     * only relevant for encryption and decryption operations, because signing and verification
+     * return no data until finish.  It is recommended to return data as early as possible, rather
+     * than buffer it.
+     *
+     * If this method returns an error code other than ErrorCode::OK, the operation is aborted and
+     * the operation handle must be invalidated.  Any future use of the handle, with this method,
+     * finish, or abort, must return ErrorCode::INVALID_OPERATION_HANDLE.
+     *
+     * == Authorization Enforcement ==
+     *
+     * Key authorization enforcement is performed primarily in begin().  The one exception is the
+     * case where the key has:
+
+     * o One or more Tag::USER_SECURE_IDs, and
+     *
+     * o Does not have a Tag::AUTH_TIMEOUT
+     *
+     * In this case, the key requires an authorization per operation, and the update method must
+     * receive a non-empty and valid HardwareAuthToken.  For the auth token to be valid, all of the
+     * following has to be true:
+     *
+     *   o The HMAC field must validate correctly.
+     *
+     *   o At least one of the Tag::USER_SECURE_ID values from the key must match at least one of
+     *     the secure ID values in the token.
+     *
+     *   o The key must have a Tag::USER_AUTH_TYPE that matches the auth type in the token.
+     *
+     *   o The challenge field in the auth token must contain the operationHandle
+     *
+     *   If any of these conditions are not met, update() must return
+     *   ErrorCode::KEY_USER_NOT_AUTHENTICATED.
+     *
+     * The caller must provide the auth token on every call to update() and finish().
+     *
+     * -- RSA keys --
+     *
+     * For signing and verification operations with Digest::NONE, this method must accept the entire
+     * block to be signed or verified in a single update.  It may not consume only a portion of the
+     * block in these cases.  However, the caller may choose to provide the data in multiple updates,
+     * and update() must accept the data this way as well.  If the caller provides more data to sign
+     * than can be used (length of data exceeds RSA key size), update() must return
+     * ErrorCode::INVALID_INPUT_LENGTH.
+     *
+     * -- ECDSA keys --
+     *
+     * For signing and verification operations with Digest::NONE, this method must accept the entire
+     * block to be signed or verified in a single update.  This method may not consume only a
+     * portion of the block.  However, the caller may choose to provide the data in multiple updates
+     * and update() must accept the data this way as well.  If the caller provides more data to sign
+     * than can be used, the data is silently truncated.  (This differs from the handling of excess
+     * data provided in similar RSA operations.  The reason for this is compatibility with legacy
+     * clients.)
+     *
+     * -- AES keys --
+     *
+     * AES GCM mode supports "associated authentication data," provided via the Tag::ASSOCIATED_DATA
+     * tag in the inParams argument.  The associated data may be provided in repeated calls
+     * (important if the data is too large to send in a single block) but must always precede data
+     * to be encrypted or decrypted.  An update call may receive both associated data and data to
+     * encrypt/decrypt, but subsequent updates must not include associated data.  If the caller
+     * provides associated data to an update call after a call that includes data to
+     * encrypt/decrypt, update() must return ErrorCode::INVALID_TAG.
+     *
+     * For GCM encryption, the AEAD tag must be appended to the ciphertext by finish().  During
+     * decryption, the last Tag::MAC_LENGTH bytes of the data provided to the last update call must
+     * be the AEAD tag.  Since a given invocation of update cannot know if it's the last invocation,
+     * it must process all but the tag length and buffer the possible tag data for processing during
+     * finish().
      *
      * @param operationHandle The operation handle returned by begin().
      *
@@ -513,16 +1177,18 @@
      * @param authToken Authentication token.  Callers that provide no token must set all numeric
      *        fields to zero and the MAC must be an empty vector.
      *
-     * @param verificationToken Verification token, used to prove that another Keymaster HAL has
-     *        verified some parameters, and to deliver the other HAL's current timestamp, if needed.
-     *        If not provided, all fields must be initialized to zero and vectors empty.
+     * @param verificationToken Verification token, used to prove that another IKeymasterDevice HAL
+     *        has verified some parameters, and to deliver the other HAL's current timestamp, if
+     *        needed.  If not provided, all fields must be initialized to zero and vectors must be
+     *        empty.
      *
      * @return error See the ErrorCode enum in types.hal.
      *
      * @return inputConsumed Amount of data that was consumed by update().  If this is less than the
      *         amount provided, the caller may provide the remainder in a subsequent call to
-     *         update() or finish().  Every call to update must consume at least one byte, and
-     *         implementations should consume as much data as reasonably possible for each call.
+     *         update() or finish().  Every call to update must consume at least one byte, unless
+     *         the input is empty, and implementations should consume as much data as reasonably
+     *         possible for each call.
      *
      * @return outParams Output parameters, used to return additional data from the operation.
      *
@@ -536,6 +1202,86 @@
     /**
      * Finalizes a cryptographic operation begun with begin() and invalidates operationHandle.
      *
+     * This method is the last one called in an operation, so all processed data must be returned.
+     *
+     * Whether it completes successfully or returns an error, this method finalizes the operation
+     * and therefore must invalidate the provided operation handle.  Any future use of the handle,
+     * with finish(), update(), or abort(), must return ErrorCode::INVALID_OPERATION_HANDLE.
+     *
+     * Signing operations return the signature as the output.  Verification operations accept the
+     * signature in the signature parameter, and return no output.
+     *
+     * == Authorization enforcement ==
+     *
+     * Key authorization enforcement is performed primarily in begin().  The exceptions are
+     * authorization per operation keys and confirmation-required keys.
+     *
+     * Authorization per operation keys are the case where the key has one or more
+     * Tag::USER_SECURE_IDs, and does not have a Tag::AUTH_TIMEOUT.  In this case, the key requires
+     * an authorization per operation, and the finish method must receive a non-empty and valid
+     * authToken.  For the auth token to be valid, all of the following has to be true:
+     *
+     *   o The HMAC field must validate correctly.
+     *
+     *   o At least one of the Tag::USER_SECURE_ID values from the key must match at least one of
+     *     the secure ID values in the token.
+     *
+     *   o The key must have a Tag::USER_AUTH_TYPE that matches the auth type in the token.
+     *
+     *   o The challenge field in the auth token must contain the operationHandle
+     *
+     *   If any of these conditions are not met, update() must return
+     *   ErrorCode::KEY_USER_NOT_AUTHENTICATED.
+     *
+     * The caller must provide the auth token on every call to update() and finish().
+     *
+     * Confirmation-required keys are keys that were generated with
+     * Tag::TRUSTED_CONFIRMATION_REQUIRED.  For these keys, when doing a signing operation the
+     * caller must pass a KeyParameter Tag::CONFIRMATION_TOKEN to finish().  Implementations must
+     * check the confirmation token by computing the 32-byte HMAC-SHA256 over all of the
+     * to-be-signed data, prefixed with the 18-byte UTF-8 encoded string "confirmation token". If
+     * the computed value does not match the Tag::CONFIRMATION_TOKEN parameter, finish() must not
+     * produce a signature and must return ErrorCode::NO_USER_CONFIRMATION.
+     *
+     * -- RSA keys --
+     *
+     * Some additional requirements, depending on the padding mode:
+     *
+     * o PaddingMode::NONE.  For unpadded signing and encryption operations, if the provided data is
+     *   shorter than the key, the data must be zero-padded on the left before
+     *   signing/encryption.  If the data is the same length as the key, but numerically larger,
+     *   finish() must return ErrorCode::INVALID_ARGUMENT.  For verification and decryption
+     *   operations, the data must be exactly as long as the key.  Otherwise, return
+     *   ErrorCode::INVALID_INPUT_LENGTH.
+     *
+     * o PaddingMode::RSA_PSS.  For PSS-padded signature operations, the PSS salt length must match
+     *   the size of the PSS digest selected.  The digest specified with Tag::DIGEST in inputParams
+     *   on begin() must be used as the PSS digest algorithm, MGF1 must be used as the mask
+     *   generation function and SHA1 must be used as the MGF1 digest algorithm.
+     *
+     * o PaddingMode::RSA_OAEP.  The digest specified with Tag::DIGEST in inputParams on begin is
+     *   used as the OAEP digest algorithm, MGF1 must be used as the mask generation function and
+     *   and SHA1 must be used as the MGF1 digest algorithm.
+     *
+     * -- ECDSA keys --
+     *
+     * If the data provided for unpadded signing or verification is too long, truncate it.
+     *
+     * -- AES keys --
+     *
+     * Some additional conditions, depending on block mode:
+     *
+     * o BlockMode::ECB or BlockMode::CBC.  If padding is PaddingMode::NONE and the data length is
+     *  not a multiple of the AES block size, finish() must return
+     *  ErrorCode::INVALID_INPUT_LENGTH.  If padding is PaddingMode::PKCS7, pad the data per the
+     *  PKCS#7 specification, including adding an additional padding block if the data is a multiple
+     *  of the block length.
+     *
+     * o BlockMode::GCM.  During encryption, after processing all plaintext, compute the tag
+     *   (Tag::MAC_LENGTH bytes) and append it to the returned ciphertext.  During decryption,
+     *   process the last Tag::MAC_LENGTH bytes as the tag.  If tag verification fails, finish()
+     *   must return ErrorCode::VERIFICATION_FAILED.
+     *
      * @param operationHandle The operation handle returned by begin().  This handle must be invalid
      *        when finish() returns.
      *
@@ -551,11 +1297,9 @@
      * @param authToken Authentication token.  Callers that provide no token must set all numeric
      *        fields to zero and the MAC must be an empty vector.
      *
-     * @param verificationToken Verification token, used to prove that another Keymaster HAL has
-     *        verified some parameters, and to deliver the other HAL's current timestamp, if needed.
-     *        If not provided, all fields must be initialized to zero and vectors empty.
-     *
-     * @return error See the ErrorCode enum in types.hal.
+     * @param verificationToken Verification token, used to prove that another IKeymasterDevice HAL
+     *        has verified some parameters, and to deliver the other HAL's current timestamp, if
+     *        needed.  If not provided, all fields must be initialized to zero and vectors empty.
      *
      * @return outParams Any output parameters generated by finish().
      *
diff --git a/keymaster/4.0/types.hal b/keymaster/4.0/types.hal
index 47fd1ed..85f181a 100644
--- a/keymaster/4.0/types.hal
+++ b/keymaster/4.0/types.hal
@@ -59,83 +59,364 @@
 enum Tag : uint32_t {
     INVALID = TagType:INVALID | 0,
 
-    /*
-     * Tags that must be semantically enforced by hardware and software implementations.
+    /**
+     * Tag::PURPOSE specifies the set of purposes for which the key may be used.  Possible values
+     * are defined in the KeyPurpose enumeration.
+     *
+     * This tag is repeatable; keys may be generated with multiple values, although an operation has
+     * a single purpose.  When begin() is called to start an operation, the purpose of the operation
+     * is specified.  If the purpose specified for the operation is not authorized by the key (the
+     * key didn't have a corresponding Tag::PURPOSE provided during generation/import), the
+     * operation must fail with ErrorCode::INCOMPATIBLE_PURPOSE.
+     *
+     * Must be hardware-enforced.
      */
+    PURPOSE = TagType:ENUM_REP | 1,
 
-    /* Crypto parameters */
-    PURPOSE = TagType:ENUM_REP | 1,    /* KeyPurpose. */
-    ALGORITHM = TagType:ENUM | 2,      /* Algorithm. */
-    KEY_SIZE = TagType:UINT | 3,       /* Key size in bits. */
+    /**
+     * Tag::ALGORITHM specifies the cryptographic algorithm with which the key is used.  This tag
+     * must be provided to generateKey and importKey, and must be specified in the wrapped key
+     * provided to importWrappedKey.
+     *
+     * Must be hardware-enforced.
+     */
+    ALGORITHM = TagType:ENUM | 2,
+
+    /**
+     * Tag::KEY_SIZE pecifies the size, in bits, of the key, measuring in the normal way for the
+     * key's algorithm.  For example, for RSA keys, Tag::KEY_SIZE specifies the size of the public
+     * modulus.  For AES keys it specifies the length of the secret key material.  For 3DES keys it
+     * specifies the length of the key material, not counting parity bits (though parity bits must
+     * be provided for import, etc.).  Since only three-key 3DES keys are supported, 3DES
+     * Tag::KEY_SIZE must be 168.
+     *
+     * Must be hardware-enforced.
+     */
+    KEY_SIZE = TagType:UINT | 3,
+
+    /**
+     * Tag::BLOCK_MODE specifies the block cipher mode(s) with which the key may be used.  This tag
+     * is only relevant to AES and 3DES keys.  Possible values are defined by the BlockMode enum.
+     *
+     * This tag is repeatable for key generation/import.  For AES and 3DES operations the caller
+     * must specify a Tag::BLOCK_MODE in the additionalParams argument of begin().  If the mode is
+     * missing or the specified mode is not in the modes specified for the key during
+     * generation/import, the operation must fail with ErrorCode::INCOMPATIBLE_BLOCK_MODE.
+     *
+     * Must be hardware-enforced.
+     */
     BLOCK_MODE = TagType:ENUM_REP | 4, /* BlockMode. */
-    DIGEST = TagType:ENUM_REP | 5,     /* Digest. */
-    PADDING = TagType:ENUM_REP | 6,    /* PaddingMode. */
-    CALLER_NONCE = TagType:BOOL | 7,   /* Allow caller to specify nonce or IV. */
-    MIN_MAC_LENGTH = TagType:UINT | 8, /* Minimum length of MAC or AEAD authentication tag in
-                                        * bits. */
-    // 9 reserved
-    EC_CURVE = TagType:ENUM | 10,      /* EcCurve. */
 
-    /* Algorithm-specific. */
+    /**
+     * Tag::DIGEST specifies the digest algorithms that may be used with the key to perform signing
+     * and verification operations.  This tag is relevant to RSA, ECDSA and HMAC keys.  Possible
+     * values are defined by the Digest enum.
+     *
+     * This tag is repeatable for key generation/import.  For signing and verification operations,
+     * the caller must specify a digest in the additionalParams argument of begin().  If the digest
+     * is missing or the specified digest is not in the digests associated with the key, the
+     * operation must fail with ErrorCode::INCOMPATIBLE_DIGEST.
+     *
+     * Must be hardware-enforced.
+     */
+    DIGEST = TagType:ENUM_REP | 5,
+
+    /**
+     * Tag::PADDING specifies the padding modes that may be used with the key.  This tag is relevant
+     * to RSA, AES and 3DES keys.  Possible values are defined by the PaddingMode enum.
+     *
+     * PaddingMode::RSA_OAEP and PaddingMode::RSA_PKCS1_1_5_ENCRYPT are used only for RSA
+     * encryption/decryption keys and specify RSA OAEP padding and RSA PKCS#1 v1.5 randomized
+     * padding, respectively.  PaddingMode::RSA_PSS and PaddingMode::RSA_PKCS1_1_5_SIGN are used
+     * only for RSA signing/verification keys and specify RSA PSS padding and RSA PKCS#1 v1.5
+     * deterministic padding, respectively.
+     *
+     * PaddingMode::NONE may be used with either RSA, AES or 3DES keys.  For AES or 3DES keys, if
+     * PaddingMode::NONE is used with block mode ECB or CBC and the data to be encrypted or
+     * decrypted is not a multiple of the AES block size in length, the call to finish() must fail
+     * with ErrorCode::INVALID_INPUT_LENGTH.
+     *
+     * PaddingMode::PKCS7 may only be used with AES and 3DES keys, and only with ECB and CBC modes.
+     *
+     * In any case, if the caller specifies a padding mode that is not usable with the key's
+     * algorithm, the generation or import method must return ErrorCode::INCOMPATIBLE_PADDING_MODE.
+     *
+     * This tag is repeatable.  A padding mode must be specified in the call to begin().  If the
+     * specified mode is not authorized for the key, the operation must fail with
+     * ErrorCode::INCOMPATIBLE_BLOCK_MODE.
+     *
+     * Must be hardware-enforced.
+     */
+    PADDING = TagType:ENUM_REP | 6,
+
+    /**
+     * Tag::CALLER_NONCE specifies that the caller can provide a nonce for nonce-requiring
+     * operations.  This tag is boolean, so the possible values are true (if the tag is present) and
+     * false (if the tag is not present).
+     *
+     * This tag is used only for AES and 3DES keys, and is only relevant for CBC, CTR and GCM block
+     * modes.  If the tag is not present in a key's authorization list, implementations must reject
+     * any operation that provides Tag::NONCE to begin() with ErrorCode::CALLER_NONCE_PROHIBITED.
+     *
+     * Must be hardware-enforced.
+     */
+    CALLER_NONCE = TagType:BOOL | 7,
+
+    /**
+     * Tag::MIN_MAC_LENGTH specifies the minimum length of MAC that can be requested or verified
+     * with this key for HMAC keys and AES keys that support GCM mode.
+     *
+     * This value is the minimum MAC length, in bits.  It must be a multiple of 8 bits.  For HMAC
+     * keys, the value must be least 64 and no more than 512.  For GCM keys, the value must be at
+     * least 96 and no more than 128.  If the provided value violates these requirements,
+     * generateKey() or importKey() must return ErrorCode::UNSUPPORTED_KEY_SIZE.
+     *
+     * Must be hardware-enforced.
+     */
+    MIN_MAC_LENGTH = TagType:UINT | 8,
+
+    // Tag 9 reserved
+
+    /**
+     * Tag::EC_CURVE specifies the elliptic curve.  EC key generation requests may have
+     * Tag:EC_CURVE, Tag::KEY_SIZE, or both.  If both are provided and the size and curve do not
+     * match, IKeymasterDevice must return ErrorCode::INVALID_ARGUMENT.
+     *
+     * Must be hardware-enforced.
+     */
+    EC_CURVE = TagType:ENUM | 10,
+
+    /**
+     * Tag::RSA_PUBLIC_EXPONENT specifies the value of the public exponent for an RSA key pair.
+     * This tag is relevant only to RSA keys, and is required for all RSA keys.
+     *
+     * The value is a 64-bit unsigned integer that satisfies the requirements of an RSA public
+     * exponent.  This value must be a prime number.  IKeymasterDevice implementations must support
+     * the value 2^16+1 and may support other reasonable values.  If no exponent is specified or if
+     * the specified exponent is not supported, key generation must fail with
+     * ErrorCode::INVALID_ARGUMENT.
+     *
+     * Must be hardware-enforced.
+     */
     RSA_PUBLIC_EXPONENT = TagType:ULONG | 200,
-    // 201 reserved for ECIES
-    INCLUDE_UNIQUE_ID = TagType:BOOL | 202, /* If true, attestation certificates for this key must
-                                             * contain an application-scoped and time-bounded
-                                             * device-unique ID.*/
 
-    /* Other hardware-enforced. */
-    BLOB_USAGE_REQUIREMENTS = TagType:ENUM | 301, /* KeyBlobUsageRequirements. */
-    BOOTLOADER_ONLY = TagType:BOOL | 302,         /* Usable only by bootloader. */
-    ROLLBACK_RESISTANCE = TagType:BOOL | 303,     /* Whether key is rollback-resistant.  Specified
-                                                   * in the key description provided to generateKey
-                                                   * or importKey if rollback resistance is desired.
-                                                   * If the implementation cannot provide rollback
-                                                   * resistance, it must return
-                                                   * ROLLBACK_RESISTANCE_UNAVAILABLE. */
+    // Tag 201 reserved
 
-    /* HARDWARE_TYPE specifies the type of the secure hardware that is requested for the key
-     * generation / import.  See the SecurityLevel enum.  In the absence of this tag, keystore must
-     * use TRUSTED_ENVIRONMENT.  If this tag is present and the requested hardware type is not
-     * available, Keymaster returns HARDWARE_TYPE_UNAVAILABLE. This tag is not included in
-     * attestations, but hardware type must be reflected in the Keymaster SecurityLevel of the
-     * attestation header. */
+    /**
+     * Tag::INCLUDE_UNIQUE_ID is specified during key generation to indicate that an attestation
+     * certificate for the generated key should contain an application-scoped and time-bounded
+     * device-unique ID.  See Tag::UNIQUE_ID.
+     *
+     * Must be hardware-enforced.
+     */
+    INCLUDE_UNIQUE_ID = TagType:BOOL | 202,
+
+    /**
+     * Tag::BLOB_USAGE_REQUIREMENTS specifies the necessary system environment conditions for the
+     * generated key to be used.  Possible values are defined by the KeyBlobUsageRequirements enum.
+     *
+     * This tag is specified by the caller during key generation or import to require that the key
+     * is usable in the specified condition.  If the caller specifies Tag::BLOB_USAGE_REQUIREMENTS
+     * with value KeyBlobUsageRequirements::STANDALONE the IKeymasterDevice must return a key blob
+     * that can be used without file system support.  This is critical for devices with encrypted
+     * disks, where the file system may not be available until after a Keymaster key is used to
+     * decrypt the disk.
+     *
+     * Must be hardware-enforced.
+     */
+    BLOB_USAGE_REQUIREMENTS = TagType:ENUM | 301,
+
+    /**
+     * Tag::BOOTLOADER_ONLY specifies only the bootloader can use the key.
+     *
+     * Any attempt to use a key with Tag::BOOTLOADER_ONLY from the Android system must fail with
+     * ErrorCode::INVALID_KEY_BLOB.
+     *
+     * Must be hardware-enforced.
+     */
+    BOOTLOADER_ONLY = TagType:BOOL | 302,
+
+    /**
+     * Tag::ROLLBACK_RESISTANCE specifies that the key has rollback resistance, meaning that when
+     * deleted with deleteKey() or deleteAllKeys(), the key is guaranteed to be permanently deleted
+     * and unusable.  It's possible that keys without this tag could be deleted and then restored
+     * from backup.
+     *
+     * This tag is specified by the caller during key generation or import to require.  If the
+     * IKeymasterDevice cannot guarantee rollback resistance for the specified key, it must return
+     * ErrorCode::ROLLBACK_RESISTANCE_UNAVAILABLE.  IKeymasterDevice implementations are not
+     * required to support rollback resistance.
+     *
+     * Must be hardwared-enforced.
+     */
+    ROLLBACK_RESISTANCE = TagType:BOOL | 303,
+
+    // Reserved for future use.
     HARDWARE_TYPE = TagType:ENUM | 304,
 
-    /*
-     * Tags that should be semantically enforced by hardware if possible and will otherwise be
-     * enforced by software (keystore).
+    /**
+     * Tag::ACTIVE_DATETIME specifies the date and time at which the key becomes active, in
+     * milliseconds since Jan 1, 1970.  If a key with this tag is used prior to the specified date
+     * and time, IKeymasterDevice::begin() must return ErrorCode::KEY_NOT_YET_VALID;
+     *
+     * Need not be hardware-enforced.
      */
+    ACTIVE_DATETIME = TagType:DATE | 400, /* Start of validity. */
 
-    /* Key validity period */
-    ACTIVE_DATETIME = TagType:DATE | 400,             /* Start of validity. */
-    ORIGINATION_EXPIRE_DATETIME = TagType:DATE | 401, /* Date when new "messages" should no longer
-                                                       * be created. */
-    USAGE_EXPIRE_DATETIME = TagType:DATE | 402,       /* Date when existing "messages" should no
-                                                       * longer be trusted. */
-    MIN_SECONDS_BETWEEN_OPS = TagType:UINT | 403,     /* Minimum elapsed time between
-                                                       * cryptographic operations with the key. */
-    MAX_USES_PER_BOOT = TagType:UINT | 404,           /* Number of times the key can be used per
-                                                       * boot. */
+    /**
+     * Tag::ORIGINATION_EXPIRE_DATETIME specifies the date and time at which the key expires for
+     * signing and encryption purposes.  After this time, any attempt to use a key with
+     * KeyPurpose::SIGN or KeyPurpose::ENCRYPT provided to begin() must fail with
+     * ErrorCode::KEY_EXPIRED.
+     *
+     * The value is a 64-bit integer representing milliseconds since January 1, 1970.
+     *
+     * Need not be hardware-enforced.
+     */
+    ORIGINATION_EXPIRE_DATETIME = TagType:DATE | 401,
 
-    /* User authentication */
-    // 500 reserved
-    USER_ID = TagType:UINT | 501,             /* Android ID of authorized user or authenticator(s), */
+    /**
+     * Tag::USAGE_EXPIRE_DATETIME specifies the date and time at which the key expires for
+     * verification and decryption purposes.  After this time, any attempt to use a key with
+     * KeyPurpose::VERIFY or KeyPurpose::DECRYPT provided to begin() must fail with
+     * ErrorCode::KEY_EXPIRED.
+     *
+     * The value is a 64-bit integer representing milliseconds since January 1, 1970.
+     *
+     * Need not be hardware-enforced.
+     */
+    USAGE_EXPIRE_DATETIME = TagType:DATE | 402,
+
+    /**
+     * Tag::MIN_SECONDS_BETWEEN_OPS specifies the minimum amount of time that elapses between
+     * allowed operations using a key.  This can be used to rate-limit uses of keys in contexts
+     * where unlimited use may enable brute force attacks.
+     *
+     * The value is a 32-bit integer representing seconds between allowed operations.
+     *
+     * When a key with this tag is used in an operation, the IKeymasterDevice must start a timer
+     * during the finish() or abort() call.  Any call to begin() that is received before the timer
+     * indicates that the interval specified by Tag::MIN_SECONDS_BETWEEN_OPS has elapsed must fail
+     * with ErrorCode::KEY_RATE_LIMIT_EXCEEDED.  This implies that the IKeymasterDevice must keep a
+     * table of use counters for keys with this tag.  Because memory is often limited, this table
+     * may have a fixed maximum size and Keymaster may fail operations that attempt to use keys with
+     * this tag when the table is full.  The table must acommodate at least 8 in-use keys and
+     * aggressively reuse table slots when key minimum-usage intervals expire.  If an operation
+     * fails because the table is full, Keymaster returns ErrorCode::TOO_MANY_OPERATIONS.
+     *
+     * Must be hardware-enforced.
+     */
+    MIN_SECONDS_BETWEEN_OPS = TagType:UINT | 403,
+
+    /**
+     * Tag::MAX_USES_PER_BOOT specifies the maximum number of times that a key may be used between
+     * system reboots.  This is another mechanism to rate-limit key use.
+     *
+     * The value is a 32-bit integer representing uses per boot.
+     *
+     * When a key with this tag is used in an operation, a key-associated counter must be
+     * incremented during the begin() call.  After the key counter has exceeded this value, all
+     * subsequent attempts to use the key must fail with ErrorCode::MAX_OPS_EXCEEDED, until the
+     * device is restarted.  This implies that the IKeymasterDevice must keep a table of use
+     * counters for keys with this tag.  Because Keymaster memory is often limited, this table can
+     * have a fixed maximum size and Keymaster can fail operations that attempt to use keys with
+     * this tag when the table is full.  The table needs to acommodate at least 8 keys.  If an
+     * operation fails because the table is full, IKeymasterDevice must
+     * ErrorCode::TOO_MANY_OPERATIONS.
+     *
+     * Must be hardware-enforced.
+     */
+    MAX_USES_PER_BOOT = TagType:UINT | 404,
+
+    /**
+     * Tag::USER_ID specifies the ID of the Android user that is permitted to use the key.
+     *
+     * Must not be hardware-enforced.
+     */
+    USER_ID = TagType:UINT | 501,
+
+    /**
+     * Tag::USER_SECURE_ID specifies that a key may only be used under a particular secure user
+     * authentication state.  This tag is mutually exclusive with Tag::NO_AUTH_REQUIRED.
+     *
+     * The value is a 64-bit integer specifying the authentication policy state value which must be
+     * present in the userId or authenticatorId field of a HardwareAuthToken provided to begin(),
+     * update(), or finish().  If a key with Tag::USER_SECURE_ID is used without a HardwareAuthToken
+     * with the matching userId or authenticatorId, the IKeymasterDevice must return
+     * ErrorCode::KEY_USER_NOT_AUTHENTICATED.
+     *
+     * Tag::USER_SECURE_ID interacts with Tag::AUTH_TIMEOUT in a very important way.  If
+     * Tag::AUTH_TIMEOUT is present in the key's characteristics then the key is a "timeout-based"
+     * key, and may only be used if the difference between the current time when begin() is called
+     * and the timestamp in the HardwareAuthToken is less than the value in Tag::AUTH_TIMEOUT * 1000
+     * (the multiplier is because Tag::AUTH_TIMEOUT is in seconds, but the HardwareAuthToken
+     * timestamp is in milliseconds).  Otherwise the IKeymasterDevice must returrn
+     * ErrorCode::KEY_USER_NOT_AUTHENTICATED.
+     *
+     * If Tag::AUTH_TIMEOUT is not present, then the key is an "auth-per-operation" key.  In this
+     * case, begin() must not require a HardwareAuthToken with appropriate contents.  Instead,
+     * update() and finish() must receive a HardwareAuthToken with Tag::USER_SECURE_ID value in
+     * userId or authenticatorId fields, and the current operation's operation handle in the
+     * challenge field.  Otherwise the IKeymasterDevice must returrn
+     * ErrorCode::KEY_USER_NOT_AUTHENTICATED.
+     *
+     * This tag is repeatable.  If repeated, and any one of the values matches the HardwareAuthToken
+     * as described above, the key is authorized for use.  Otherwise the operation must fail with
+     * ErrorCode::KEY_USER_NOT_AUTHENTICATED.
+     *
+     * Must be hardware-enforced.
+     */
     USER_SECURE_ID = TagType:ULONG_REP | 502, /* Secure ID of authorized user or authenticator(s).
-                                               * Disallowed if NO_AUTH_REQUIRED is present. */
-    NO_AUTH_REQUIRED = TagType:BOOL | 503,    /* If key is usable without authentication. */
-    USER_AUTH_TYPE = TagType:ENUM | 504,      /* Bitmask of authenticator types allowed when
-                                               * USER_SECURE_ID contains a secure user ID, rather
-                                               * than a secure authenticator ID.  Defined in
-                                               * HardwareAuthenticatorType. */
-    AUTH_TIMEOUT = TagType:UINT | 505,        /* Required freshness of user authentication for
-                                               * private/secret key operations, in seconds.  Public
-                                               * key operations require no authentication.  If
-                                               * absent, authentication is required for every use.
-                                               * Authentication state is lost when the device is
-                                               * powered off. */
-    ALLOW_WHILE_ON_BODY =  TagType:BOOL | 506, /* Allow key to be used after authentication timeout
-                                                * if device is still on-body (requires secure
-                                                * on-body sensor. */
+                                                 * Disallowed if NO_AUTH_REQUIRED is present. */
+
+    /**
+     * Tag::NO_AUTH_REQUIRED specifies that no authentication is required to use this key.  This tag
+     * is mutually exclusive with Tag::USER_SECURE_ID.
+     *
+     * Must be hardware-enforced.
+     */
+    NO_AUTH_REQUIRED = TagType:BOOL | 503, /* If key is usable without authentication. */
+
+    /**
+     * Tag::USER_AUTH_TYPE specifies the types of user authenticators that may be used to authorize
+     * this key.
+     *
+     * The value is one or more values from HardwareAuthenticatorType, ORed together.
+     *
+     * When IKeymasterDevice is requested to perform an operation with a key with this tag, it must
+     * receive a HardwareAuthToken and one or more bits must be set in both the HardwareAuthToken's
+     * authenticatorType field and the Tag::USER_AUTH_TYPE value.  That is, it must be true that
+     *
+     *    (token.authenticatorType & tag_user_auth_type) != 0
+     *
+     * where token.authenticatorType is the authenticatorType field of the HardwareAuthToken and
+     * tag_user_auth_type is the value of Tag:USER_AUTH_TYPE.
+     *
+     * Must be hardware-enforced.
+     */
+    USER_AUTH_TYPE = TagType:ENUM | 504,
+
+    /**
+     * Tag::AUTH_TIMEOUT specifies the time in seconds for which the key is authorized for use,
+     * after user authentication.  If
+     * Tag::USER_SECURE_ID is present and this tag is not, then the key requies authentication for
+     * every usage (see begin() for the details of the authentication-per-operation flow).
+     *
+     * The value is a 32-bit integer specifying the time in seconds after a successful
+     * authentication of the user specified by Tag::USER_SECURE_ID with the authentication method
+     * specified by Tag::USER_AUTH_TYPE that the key can be used.
+     *
+     * Must be hardware-enforced.
+     */
+    AUTH_TIMEOUT = TagType:UINT | 505,
+
+    /**
+     * Tag::ALLOW_WHILE_ON_BODY specifies that the key may be used after authentication timeout if
+     * device is still on-body (requires on-body sensor).
+     *
+     * Cannot be hardware-enforced.
+     */
+    ALLOW_WHILE_ON_BODY = TagType:BOOL | 506,
 
     /**
      * TRUSTED_USER_PRESENCE_REQUIRED is an optional feature that specifies that this key must be
@@ -166,7 +447,7 @@
      *     the non-secure world, which means an attacker who has compromised Android can spoof
      *     password authentication.
      *
-     * Note that no mechanism is defined for delivering proof of presence to Keymaster,
+     * Note that no mechanism is defined for delivering proof of presence to an IKeymasterDevice,
      * except perhaps as implied by an auth token.  This means that Keymaster must be able to check
      * proof of presence some other way.  Further, the proof of presence must be performed between
      * begin() and the first call to update() or finish().  If the first update() or the finish()
@@ -182,108 +463,408 @@
      */
     TRUSTED_USER_PRESENCE_REQUIRED = TagType:BOOL | 507,
 
-    /** TRUSTED_CONFIRMATION_REQUIRED is only applicable to keys with KeyPurpose SIGN, and specifies
-     *  that this key must not be usable unless the user provides confirmation of the data to be
-     *  signed. Confirmation is proven to keymaster via an approval token. See CONFIRMATION_TOKEN,
-     *  as well as the ConfirmatinUI HAL.
+    /** Tag::TRUSTED_CONFIRMATION_REQUIRED is only applicable to keys with KeyPurpose SIGN, and
+     *  specifies that this key must not be usable unless the user provides confirmation of the data
+     *  to be signed.  Confirmation is proven to keymaster via an approval token.  See
+     *  CONFIRMATION_TOKEN, as well as the ConfirmatinUI HAL.
      *
      * If an attempt to use a key with this tag does not have a cryptographically valid
      * CONFIRMATION_TOKEN provided to finish() or if the data provided to update()/finish() does not
      * match the data described in the token, keymaster must return NO_USER_CONFIRMATION. */
     TRUSTED_CONFIRMATION_REQUIRED = TagType:BOOL | 508,
 
-    UNLOCKED_DEVICE_REQUIRED = TagType:BOOL | 509, /* Require the device screen to be unlocked if
-                                                    * the key is used. */
+    /**
+     *
+     */
+    UNLOCKED_DEVICE_REQUIRED = TagType:BOOL | 509,
 
-    /* Application access control */
-    APPLICATION_ID = TagType:BYTES | 601, /* Byte string identifying the authorized application. */
+    /**
+     * Tag::APPLICATION_ID.  When provided to generateKey or importKey, this tag specifies data
+     * that is necessary during all uses of the key.  In particular, calls to exportKey() and
+     * getKeyCharacteristics() must provide the same value to the clientId parameter, and calls to
+     * begin must provide this tag and the same associated data as part of the inParams set.  If
+     * the correct data is not provided, the method must return ErrorCode::INVALID_KEY_BLOB.
+     *
+     * The content of this tag must be bound to the key cryptographically, meaning it must not be
+     * possible for an adversary who has access to all of the secure world secrets but does not have
+     * access to the tag content to decrypt the key without brute-forcing the tag content, which
+     * applications can prevent by specifying sufficiently high-entropy content.
+     *
+     * Must be hardware-enforced.
+     */
+    APPLICATION_ID = TagType:BYTES | 601,
 
     /*
      * Semantically unenforceable tags, either because they have no specific meaning or because
      * they're informational only.
      */
-    APPLICATION_DATA = TagType:BYTES | 700, /* Data provided by authorized application. */
-    CREATION_DATETIME = TagType:DATE | 701, /* Key creation time */
-    ORIGIN = TagType:ENUM | 702,            /* keymaster_key_origin_t. */
-    // 703 is unused.
-    ROOT_OF_TRUST = TagType:BYTES | 704,         /* Root of trust ID. */
-    OS_VERSION = TagType:UINT | 705,             /* Version of system (keymaster2) */
-    OS_PATCHLEVEL = TagType:UINT | 706,          /* Patch level of system (keymaster2) */
-    UNIQUE_ID = TagType:BYTES | 707,             /* Used to provide unique ID in attestation */
-    ATTESTATION_CHALLENGE = TagType:BYTES | 708, /* Used to provide challenge in attestation */
-    ATTESTATION_APPLICATION_ID = TagType:BYTES | 709, /* Used to identify the set of possible
-                                                       * applications of which one has initiated a
-                                                       * key attestation */
-    ATTESTATION_ID_BRAND = TagType:BYTES | 710,   /* Used to provide the device's brand name to be
-                                                   * included in attestation */
-    ATTESTATION_ID_DEVICE = TagType:BYTES | 711,  /* Used to provide the device's device name to
-                                                   * be included in attestation */
-    ATTESTATION_ID_PRODUCT = TagType:BYTES | 712, /* Used to provide the device's product name to
-                                                   * be included in attestation */
-    ATTESTATION_ID_SERIAL =
-    TagType:BYTES | 713,                       /* Used to provide the device's serial number to be
-                                                * included in attestation */
-    ATTESTATION_ID_IMEI = TagType:BYTES | 714, /* Used to provide the device's IMEI to be included
-                                                * in attestation */
-    ATTESTATION_ID_MEID = TagType:BYTES | 715, /* Used to provide the device's MEID to be included
-                                                * in attestation */
-    ATTESTATION_ID_MANUFACTURER =
-    TagType:BYTES | 716,                        /* Used to provide the device's manufacturer
-                                                 * name to be included in attestation */
-    ATTESTATION_ID_MODEL = TagType:BYTES | 717, /* Used to provide the device's model name to be
-                                                 * included in attestation */
 
     /**
-     * Patch level of vendor image.  The value is an integer of the form YYYYMM, where YYYY is the
-     * four-digit year when the vendor image was released and MM is the two-digit month.  During
-     * each boot, the bootloader must provide the patch level of the vendor image to keymaser
-     * (mechanism is implemntation-defined).  When keymaster keys are created or updated, the
-     * VENDOR_PATCHLEVEL tag must be cryptographically bound to the keys, with the current value as
-     * provided by the bootloader.  When keys are used, keymaster must verify that the
-     * VENDOR_PATCHLEVEL bound to the key matches the current value.  If they do not match,
-     * keymaster must return ErrorCode::KEY_REQUIRES_UPGRADE.  The client must then call upgradeKey.
+     * Tag::APPLICATION_DATA.  When provided to generateKey or importKey, this tag specifies data
+     * that is necessary during all uses of the key.  In particular, calls to exportKey() and
+     * getKeyCharacteristics() must provide the same value to the appData parameter, and calls to
+     * begin must provide this tag and the same associated data as part of the inParams set.  If
+     * the correct data is not provided, the method must return ErrorCode::INVALID_KEY_BLOB.
+     *
+     * The content of this tag msut be bound to the key cryptographically, meaning it must not be
+     * possible for an adversary who has access to all of the secure world secrets but does not have
+     * access to the tag content to decrypt the key without brute-forcing the tag content, which
+     * applications can prevent by specifying sufficiently high-entropy content.
+     *
+     * Must be hardware-enforced.
+     */
+    APPLICATION_DATA = TagType:BYTES | 700,
+
+    /**
+     * Tag::CREATION_DATETIME specifies the date and time the key was created, in milliseconds since
+     * January 1, 1970.  This tag is optional and informational only.
+     *
+     * Tag::CREATED is informational only, and not enforced by anything.  Must be in the
+     * software-enforced list, if provided.
+     */
+    CREATION_DATETIME = TagType:DATE | 701,
+
+    /**
+     * Tag::ORIGIN specifies where the key was created, if known.  This tag must not be specified
+     * during key generation or import, and must be added to the key characteristics by the
+     * IKeymasterDevice.  The possible values are defined in the KeyOrigin enum.
+     *
+     * Must be hardware-enforced.
+     */
+    ORIGIN = TagType:ENUM | 702,
+
+    // 703 is unused.
+
+    /**
+     * Tag::ROOT_OF_TRUST specifies the root of trust, the key used by verified boot to validate the
+     * operating system booted (if any).  This tag is never provided to or returned from Keymaster
+     * in the key characteristics.  It exists only to define the tag for use in the attestation
+     * record.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ROOT_OF_TRUST = TagType:BYTES | 704,
+
+    /**
+     * Tag::OS_VERSION specifies the system OS version with which the key may be used.  This tag is
+     * never sent to the IKeymasterDevice, but is added to the hardware-enforced authorization list
+     * by the TA.  Any attempt to use a key with a Tag::OS_VERSION value different from the
+     * currently-running OS version must cause begin(), getKeyCharacteristics() or exportKey() to
+     * return ErrorCode::KEY_REQUIRES_UPGRADE.  See upgradeKey() for details.
+     *
+     * The value of the tag is an integer of the form MMmmss, where MM is the major version number,
+     * mm is the minor version number, and ss is the sub-minor version number.  For example, for a
+     * key generated on Android version 4.0.3, the value would be 040003.
+     *
+     * The IKeymasterDevice HAL must read the current OS version from the system property
+     * ro.build.id and deliver it to the secure environment when the HAL is first loaded (mechanism
+     * is implementation-defined).  The secure environment must not accept another version until
+     * after the next boot.  If the content of ro.build.id has additional version information after
+     * the sub-minor version number, it must not be included in Tag::OS_VERSION.  If the content is
+     * non-numeric, the secure environment must use 0 as the system version.
+     *
+     * Must be hardware-enforced.
+     */
+    OS_VERSION = TagType:UINT | 705,
+
+    /**
+     * Tag::OS_PATCHLEVEL specifies the system security patch level with which the key may be used.
+     * This tag is never sent to the keymaster TA, but is added to the hardware-enforced
+     * authorization list by the TA.  Any attempt to use a key with a Tag::OS_PATCHLEVEL value
+     * different from the currently-running system patchlevel must cause begin(),
+     * getKeyCharacteristics() or exportKey() to return ErrorCode::KEY_REQUIRES_UPGRADE.  See
+     * upgradeKey() for details.
+     *
+     * The value of the tag is an integer of the form YYYYMM, where YYYY is the four-digit year of
+     * the last update and MM is the two-digit month of the last update.  For example, for a key
+     * generated on an Android device last updated in December 2015, the value would be 201512.
+     *
+     * The IKeymasterDevice HAL must read the current system patchlevel from the system property
+     * ro.build.version.security_patch and deliver it to the secure environment when the HAL is
+     * first loaded (mechanism is implementation-defined).  The secure environment must not accept
+     * another patchlevel until after the next boot.
+     *
+     * Must be hardware-enforced.
+     */
+    OS_PATCHLEVEL = TagType:UINT | 706,
+
+    /**
+     * Tag::UNIQUE_ID specifies a unique, time-based identifier.  This tag is never provided to or
+     * returned from Keymaster in the key characteristics.  It exists only to define the tag for use
+     * in the attestation record.
+     *
+     * When a key with Tag::INCLUDE_UNIQUE_ID is attested, the unique ID is added to the attestation
+     * record.  The value is a 128-bit hash that is unique per device and per calling application,
+     * and changes monthly and on most password resets.  It is computed with:
+     *
+     *    HMAC_SHA256(T || C || R, HBK)
+     *
+     * Where:
+     *
+     *    T is the "temporal counter value", computed by dividing the value of
+     *      Tag::CREATION_DATETIME by 2592000000, dropping any remainder.  T changes every 30 days
+     *      (2592000000 = 30 * 24 * 60 * 60 * 1000).
+     *
+     *    C is the value of Tag::ATTESTATION_APPLICATION_ID that is provided to attestKey().
+     *
+     *    R is 1 if Tag::RESET_SINCE_ID_ROTATION was provided to attestKey or 0 if the tag was not
+     *      provided.
+     *
+     *    HBK is a unique hardware-bound secret known to the secure environment and never revealed
+     *    by it.  The secret must contain at least 128 bits of entropy and be unique to the
+     *    individual device (probabilistic uniqueness is acceptable).
+     *
+     *    HMAC_SHA256 is the HMAC function, with SHA-2-256 as the hash.
+     *
+     * The output of the HMAC function must be truncated to 128 bits.
+     *
+     * Must be hardware-enforced.
+     */
+    UNIQUE_ID = TagType:BYTES | 707,
+
+    /**
+     * Tag::ATTESTATION_CHALLENGE is used to deliver a "challenge" value to the attestKey() method,
+     * which must place the value in the KeyDescription SEQUENCE of the attestation extension.  See
+     * attestKey().
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_CHALLENGE = TagType:BYTES | 708, /* Used to provide challenge in attestation */
+
+    /**
+     * Tag::ATTESTATION_APPLICATION_ID identifies the set of applications which may use a key, used
+     * only with attestKey().
+     *
+     * The content of Tag::ATTESTATION_APPLICATION_ID is a DER-encoded ASN.1 structure, with the
+     * following schema:
+     *
+     * AttestationApplicationId ::= SEQUENCE {
+     *     packageInfoRecords SET OF PackageInfoRecord,
+     *     signatureDigests   SET OF OCTET_STRING,
+     * }
+     *
+     * PackageInfoRecord ::= SEQUENCE {
+     *     packageName        OCTET_STRING,
+     *     version            INTEGER,
+     * }
+     *
+     * See system/security/keystore/keystore_attestation_id.cpp for details of construction.
+     * IKeymasterDevice implementers do not need to create or parse the ASN.1 structure, but only
+     * copy the tag value into the attestation record.  The DER-encoded string must not exceed 1 KiB
+     * in length.
+     *
+     * Cannot be hardware-enforced.
+     */
+    ATTESTATION_APPLICATION_ID = TagType:BYTES | 709,
+
+    /**
+     * Tag::ATTESTATION_ID_BRAND provides the device's brand name, as returned by Build.BRAND in
+     * Android, to attestKey().  This field is set only when requesting attestation of the device's
+     * identifiers.
+     *
+     * If the device does not support ID attestation (or destroyAttestationIds() was previously
+     * called and the device can no longer attest its IDs), any key attestation request that
+     * includes this tag must fail with ErrorCode::CANNOT_ATTEST_IDS.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_ID_BRAND = TagType:BYTES | 710,
+
+    /**
+     * Tag::ATTESTATION_ID_DEVICE provides the device's device name, as returned by Build.DEVICE in
+     * Android, to attestKey().  This field is set only when requesting attestation of the device's
+     * identifiers.
+     *
+     * If the device does not support ID attestation (or destroyAttestationIds() was previously
+     * called and the device can no longer attest its IDs), any key attestation request that
+     * includes this tag must fail with ErrorCode::CANNOT_ATTEST_IDS.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_ID_DEVICE = TagType:BYTES | 711,
+
+    /**
+     * Tag::ATTESTATION_ID_PRODUCT provides the device's product name, as returned by Build.PRODUCT
+     * in Android, to attestKey().  This field is set only when requesting attestation of the
+     * device's identifiers.
+     *
+     * If the device does not support ID attestation (or destroyAttestationIds() was previously
+     * called and the device can no longer attest its IDs), any key attestation request that
+     * includes this tag must fail with ErrorCode::CANNOT_ATTEST_IDS.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_ID_PRODUCT = TagType:BYTES | 712,
+
+    /**
+     * Tag::ATTESTATION_ID_SERIAL the device's serial number.  This field is set only when
+     * requesting attestation of the device's identifiers.
+     *
+     * If the device does not support ID attestation (or destroyAttestationIds() was previously
+     * called and the device can no longer attest its IDs), any key attestation request that
+     * includes this tag must fail with ErrorCode::CANNOT_ATTEST_IDS.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_ID_SERIAL = TagType:BYTES | 713,
+
+    /**
+     * Tag::ATTESTATION_ID_IMEI provides the IMEIs for all radios on the device to attestKey().
+     * This field is set only when requesting attestation of the device's identifiers.
+     *
+     * If the device does not support ID attestation (or destroyAttestationIds() was previously
+     * called and the device can no longer attest its IDs), any key attestation request that
+     * includes this tag must fail with ErrorCode::CANNOT_ATTEST_IDS.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_ID_IMEI = TagType:BYTES | 714, /* Used to provide the device's IMEI to be included
+                                                  * in attestation */
+
+    /**
+     * Tag::ATTESTATION_ID_MEID provides the MEIDs for all radios on the device to attestKey().
+     * This field will only be set when requesting attestation of the device's identifiers.
+     *
+     * If the device does not support ID attestation (or destroyAttestationIds() was previously
+     * called and the device can no longer attest its IDs), any key attestation request that
+     * includes this tag must fail with ErrorCode::CANNOT_ATTEST_IDS.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_ID_MEID = TagType:BYTES | 715, /* Used to provide the device's MEID to be included
+                                                  * in attestation */
+
+    /**
+     * Tag::ATTESTATION_ID_MANUFACTURER provides the device's manufacturer name, as returned by
+     * Build.MANUFACTURER in Android, to attstKey().  This field is set only when requesting
+     * attestation of the device's identifiers.
+     *
+     * If the device does not support ID attestation (or destroyAttestationIds() was previously
+     * called and the device can no longer attest its IDs), any key attestation request that
+     * includes this tag must fail with ErrorCode::CANNOT_ATTEST_IDS.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_ID_MANUFACTURER = TagType:BYTES | 716,
+
+    /**
+     * Tag::ATTESTATION_ID_MODEL provides the device's model name, as returned by Build.MODEL in
+     * Android, to attestKey().  This field is set only when requesting attestation of the device's
+     * identifiers.
+     *
+     * If the device does not support ID attestation (or destroyAttestationIds() was previously
+     * called and the device can no longer attest its IDs), any key attestation request that
+     * includes this tag must fail with ErrorCode::CANNOT_ATTEST_IDS.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    ATTESTATION_ID_MODEL = TagType:BYTES | 717,
+
+    /**
+     * Tag::VENDOR_PATCHLEVEL specifies the vendor image security patch level with which the key may
+     * be used.  This tag is never sent to the keymaster TA, but is added to the hardware-enforced
+     * authorization list by the TA.  Any attempt to use a key with a Tag::VENDOR_PATCHLEVEL value
+     * different from the currently-running system patchlevel must cause begin(),
+     * getKeyCharacteristics() or exportKey() to return ErrorCode::KEY_REQUIRES_UPGRADE.  See
+     * upgradeKey() for details.
+     *
+     * The value of the tag is an integer of the form YYYYMMDD, where YYYY is the four-digit year of
+     * the last update, MM is the two-digit month and DD is the two-digit day of the last
+     * update.  For example, for a key generated on an Android device last updated on June 5, 2018,
+     * the value would be 20180605.
+     *
+     * The IKeymasterDevice HAL must read the current vendor patchlevel from the system property
+     * ro.vendor.build.security_patch and deliver it to the secure environment when the HAL is first
+     * loaded (mechanism is implementation-defined).  The secure environment must not accept another
+     * patchlevel until after the next boot.
+     *
+     * Must be hardware-enforced.
      */
     VENDOR_PATCHLEVEL = TagType:UINT | 718,
 
     /**
-     * Patch level of boot image.  The value is an integer of the form YYYYMM, where YYYY is the
-     * four-digit year when the boot image was released and MM is the two-digit month.  During each
-     * boot, the bootloader must provide the patch level of the boot image to keymaser (mechanism is
-     * implemntation-defined).  When keymaster keys are created or updated, the BOOT_PATCHLEVEL tag
-     * must be cryptographically bound to the keys, with the current value as provided by the
-     * bootloader.  When keys are used, keymaster must verify that the BOOT_PATCHLEVEL bound to the
-     * key matches the current value.  If they do not match, keymaster must return
-     * ErrorCode::KEY_REQUIRES_UPGRADE.  The client must then call upgradeKey.
+     * Tag::BOOT_PATCHLEVEL specifies the boot image (kernel) security patch level with which the
+     * key may be used.  This tag is never sent to the keymaster TA, but is added to the
+     * hardware-enforced authorization list by the TA.  Any attempt to use a key with a
+     * Tag::BOOT_PATCHLEVEL value different from the currently-running system patchlevel must
+     * cause begin(), getKeyCharacteristics() or exportKey() to return
+     * ErrorCode::KEY_REQUIRES_UPGRADE.  See upgradeKey() for details.
+     *
+     * The value of the tag is an integer of the form YYYYMMDD, where YYYY is the four-digit year of
+     * the last update, MM is the two-digit month and DD is the two-digit day of the last
+     * update.  For example, for a key generated on an Android device last updated on June 5, 2018,
+     * the value would be 20180605.  If the day is not known, 00 may be substituted.
+     *
+     * During each boot, the bootloader must provide the patch level of the boot image to the secure
+     * envirionment (mechanism is implementation-defined).
+     *
+     * Must be hardware-enforced.
      */
     BOOT_PATCHLEVEL = TagType:UINT | 719,
 
-    /* Tags used only to provide data to or receive data from operations */
-    ASSOCIATED_DATA = TagType:BYTES | 1000, /* Used to provide associated data for AEAD modes. */
-    NONCE = TagType:BYTES | 1001,           /* Nonce or Initialization Vector */
-    MAC_LENGTH = TagType:UINT | 1003,       /* MAC or AEAD authentication tag length in bits. */
-
-    RESET_SINCE_ID_ROTATION = TagType:BOOL | 1004, /* Whether the device has beeen factory reset
-                                                    * since the last unique ID rotation.  Used for
-                                                    * key attestation. */
+    /**
+     * Tag::ASSOCIATED_DATA Provides "associated data" for AES-GCM encryption or decryption.  This
+     * tag is provided to update and specifies data that is not encrypted/decrypted, but is used in
+     * computing the GCM tag.
+     *
+     * Must never appear KeyCharacteristics.
+     */
+    ASSOCIATED_DATA = TagType:BYTES | 1000,
 
     /**
-     * CONFIRMATION_TOKEN is used to deliver a cryptographic token proving that the user confirmed a
-     * signing request. The content is a full-length HMAC-SHA256 value. See the ConfirmationUI HAL
-     * for details of token computation.
+     * Tag::NONCE is used to provide or return a nonce or Initialization Vector (IV) for AES-GCM,
+     * AES-CBC, AES-CTR, or 3DES-CBC encryption or decryption.  This tag is provided to begin during
+     * encryption and decryption operations.  It is only provided to begin if the key has
+     * Tag::CALLER_NONCE.  If not provided, an appropriate nonce or IV will be randomly generated by
+     * Keymaster and returned from begin.
+     *
+     * The value is a blob, an arbitrary-length array of bytes.  Allowed lengths depend on the mode:
+     * GCM nonces are 12 bytes in length; AES-CBC and AES-CTR IVs are 16 bytes in length, 3DES-CBC
+     * IVs are 8 bytes in length.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    NONCE = TagType:BYTES | 1001,
+
+    /**
+     * Tag::MAC_LENGTH provides the requested length of a MAC or GCM authentication tag, in bits.
+     *
+     * The value is the MAC length in bits.  It must be a multiple of 8 and at least as large as the
+     * value of Tag::MIN_MAC_LENGTH associated with the key.  Otherwise, begin() must return
+     * ErrorCode::INVALID_MAC_LENGTH.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    MAC_LENGTH = TagType:UINT | 1003,
+
+    /**
+     * Tag::RESET_SINCE_ID_ROTATION specifies whether the device has been factory reset since the
+     * last unique ID rotation.  Used for key attestation.
+     *
+     * Must never appear in KeyCharacteristics.
+     */
+    RESET_SINCE_ID_ROTATION = TagType:BOOL | 1004,
+
+    /**
+     * Tag::CONFIRMATION_TOKEN is used to deliver a cryptographic token proving that the user
+     * confirmed a signing request.  The content is a full-length HMAC-SHA256 value.  See the
+     * ConfirmationUI HAL for details of token computation.
+     *
+     * Must never appear in KeyCharacteristics.
      */
     CONFIRMATION_TOKEN = TagType:BYTES | 1005,
 };
 
 /**
- * Algorithms provided by keymaser implementations.
+ * Algorithms provided by IKeymasterDevice implementations.
  */
 enum Algorithm : uint32_t {
     /** Asymmetric algorithms. */
     RSA = 1,
-    // DSA = 2, -- Removed, do not re-use value 2.
+    // 2 removed, do not reuse.
     EC = 3,
 
-    /** Block ciphers algorithms */
+    /** Block cipher algorithms */
     AES = 32,
     TRIPLE_DES = 33,
 
@@ -393,12 +974,12 @@
  * Possible purposes of a key (or pair).
  */
 enum KeyPurpose : uint32_t {
-    ENCRYPT = 0,    /* Usable with RSA, EC and AES keys. */
-    DECRYPT = 1,    /* Usable with RSA, EC and AES keys. */
-    SIGN = 2,       /* Usable with RSA, EC and HMAC keys. */
-    VERIFY = 3,     /* Usable with RSA, EC and HMAC keys. */
+    ENCRYPT = 0, /* Usable with RSA, EC and AES keys. */
+    DECRYPT = 1, /* Usable with RSA, EC and AES keys. */
+    SIGN = 2,    /* Usable with RSA, EC and HMAC keys. */
+    VERIFY = 3,  /* Usable with RSA, EC and HMAC keys. */
     /* 4 is reserved */
-    WRAP_KEY = 5,   /* Usable with wrapping keys. */
+    WRAP_KEY = 5, /* Usable with wrapping keys. */
 };
 
 /**
@@ -481,6 +1062,8 @@
     VERSION_MISMATCH = -101,
 
     UNKNOWN_ERROR = -1000,
+
+    // Implementer's namespace for error codes starts at -10000.
 };
 
 /**
@@ -521,39 +1104,10 @@
     SOFTWARE = 0,
     TRUSTED_ENVIRONMENT = 1,
     /**
-     * STRONGBOX specifies that the secure hardware satisfies the following requirements:
-     *
-     *    a) Has a discrete CPU.  The StrongBox device must not be the same CPU that is used to run
-     *       the Android non-secure world, or any other untrusted code.  The StrongBox CPU must not
-     *       share cache, RAM or any other critical resources with any device that runs untrusted
-     *       code.
-     *
-     *    b) Has integral secure storage.  The StrongBox device must have its own non-volatile
-     *       storage that is not accessible by any other hardware component.
-     *
-     *    c) Has a high-quality True Random Number Generator.  The StrongBox device must have sole
-     *       control of and access to a high-quality TRNG which it uses for generating necessary
-     *       random bits.  It must combine the output of this TRNG with caller-provided entropy in a
-     *       strong CPRNG, as do non-Strongbox Keymaster implementations.
-     *
-     *    d) Is enclosed in tamper-resistant packaging.  The StrongBox device must have
-     *       tamper-resistant packaging which provides obstacles to physical penetration which are
-     *       higher than those provided by normal integrated circuit packages.
-     *
-     *    e) Provides side-channel resistance.  The StrongBox device must implement resistance
-     *       against common side-channel attacks, including power analysis, timing analysis, EM
-     *       snooping, etc.
-     *
-     * Devices with StrongBox Keymasters must also have a non-StrongBox Keymaster, which lives in
-     * the higher-performance TEE.  Keystore must load both StrongBox (if available) and
-     * non-StrongBox HALs and route key generation/import requests appropriately.  Callers that want
-     * StrongBox keys must add Tag::HARDWARE_TYPE with value SecurityLevel::STRONGBOX to the key
-     * description provided to generateKey or importKey.  Keytore must route the request to a
-     * StrongBox HAL (a HAL whose isStrongBox method returns true).  Keymaster implementations that
-     * receive a request for a Tag::HARDWARE_TYPE that is inappropriate must fail with
-     * ErrorCode::HARDWARE_TYPE_UNAVAILABLE.
+     * STRONGBOX specifies that the secure hardware satisfies the requirements specified in CDD
+     * 9.11.2.
      */
-    STRONGBOX = 2,              /* See IKeymaster::isStrongBox */
+    STRONGBOX = 2,
 };
 
 /**
@@ -564,17 +1118,19 @@
     X509 = 0,
     /** PCKS#8 format, asymmetric key pair import. */
     PKCS8 = 1,
-    /** Raw bytes, for symmetric key import and export. */
+    /** Raw bytes, for symmetric key import. */
     RAW = 3,
 };
 
 struct KeyParameter {
     /**
-     * Discriminates the uinon/blob field used.  The blob cannot be coincided with the union, but
-     * only one of "f" and "blob" is ever used at a time. */
+     * Discriminates the union/blob field used.  The blob cannot be placed in the union, but only
+     * one of "f" and "blob" may ever be used at a time.
+     */
     Tag tag;
+
     union IntegerParams {
-        /** Enum types */
+        /* Enum types */
         Algorithm algorithm;
         BlockMode blockMode;
         PaddingMode paddingMode;
@@ -587,7 +1143,7 @@
         HardwareAuthenticatorType hardwareAuthenticatorType;
         SecurityLevel hardwareType;
 
-        /** Other types */
+        /* Other types */
         bool boolValue;  // Always true, if a boolean tag is present.
         uint32_t integer;
         uint64_t longInteger;
@@ -597,20 +1153,68 @@
     vec<uint8_t> blob;
 };
 
+/**
+ * KeyCharacteristics defines the attributes of a key, including cryptographic parameters, and usage
+ * restrictions.  It consits of two vectors of KeyParameters, one for "softwareEnforced" attributes
+ * and one for "hardwareEnforced" attributes.
+ *
+ * KeyCharacteristics objects are returned by generateKey, importKey, importWrappedKey and
+ * getKeyCharacteristics.  The IKeymasterDevice secure environment is responsible for allocating the
+ * parameters, all of which are Tags with associated values, to the correct vector.  The
+ * hardwareEnforced vector must contain only those attributes which are enforced by secure hardware.
+ * All others should be in the softwareEnforced vector.  See the definitions of individual Tag enums
+ * for specification of which must be hardware-enforced, which may be software-enforced and which
+ * must never appear in KeyCharacteristics.
+ */
 struct KeyCharacteristics {
     vec<KeyParameter> softwareEnforced;
     vec<KeyParameter> hardwareEnforced;
 };
 
 /**
- * Data used to prove successful authentication.
+ * HardwareAuthToken is used to prove successful user authentication, to unlock the use of a key.
+ *
+ * HardwareAuthTokens are produced by other secure environment applications, notably GateKeeper and
+ * Fingerprint, in response to successful user authentication events.  These tokens are passed to
+ * begin(), update(), and finish() to prove that authentication occurred.  See those methods for
+ * more details.  It is up to the caller to determine which of the generated auth tokens is
+ * appropriate for a given key operation.
  */
 struct HardwareAuthToken {
+    /**
+     * challenge is a value that's used to enable authentication tokens to authorize specific
+     * events.  The primary use case for challenge is to authorize an IKeymasterDevice cryptographic
+     * operation, for keys that require authentication per operation. See begin() for details.
+     */
     uint64_t challenge;
-    uint64_t userId;             // Secure User ID, not Android user ID.
-    uint64_t authenticatorId;    // Secure authenticator ID.
+
+    /**
+     *  userId is the a "secure" user ID.  It is not related to any Android user ID or UID, but is
+     *  created in the Gatekeeper application in the secure environment.
+     */
+    uint64_t userId;
+
+    /**
+     *  authenticatorId is the a "secure" user ID.  It is not related to any Android user ID or UID,
+     *  but is created in an authentication application in the secure environment, such as the
+     *  Fingerprint application.
+     */
+    uint64_t authenticatorId;  // Secure authenticator ID.
+
+    /**
+     * authenticatorType describes the type of authentication that took place, e.g. password or
+     * fingerprint.
+     */
     HardwareAuthenticatorType authenticatorType;
+
+    /**
+     * timestamp indicates when the user authentication took place, in milliseconds since some
+     * starting point (generally the most recent device boot) which all of the applications within
+     * one secure environment must agree upon.  This timestamp is used to determine whether or not
+     * the authentication occurred recently enough to unlock a key (see Tag::AUTH_TIMEOUT).
+     */
     Timestamp timestamp;
+
     /**
      * MACs are computed with a backward-compatible method, used by Keymaster 3.0, Gatekeeper 1.0
      * and Fingerprint 1.0, as well as pre-treble HALs.
@@ -623,7 +1227,8 @@
      * where ``||'' represents concatenation, the leading zero is a single byte, and all integers
      * are represented as unsigned values, the full width of the type.  The challenge, userId and
      * authenticatorId values are in machine order, but authenticatorType and timestamp are in
-     * network order.  This odd construction is compatible with the hw_auth_token_t structure,
+     * network order (big-endian).  This odd construction is compatible with the hw_auth_token_t
+     * structure,
      *
      * Note that mac is a vec rather than an array, not because it's actually variable-length but
      * because it could be empty.  As documented in the IKeymasterDevice::begin,