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().
      *