diff --git a/common/support/Android.bp b/common/support/Android.bp
index b24893b..718901e 100644
--- a/common/support/Android.bp
+++ b/common/support/Android.bp
@@ -11,7 +11,11 @@
     name: "libaidlcommonsupport",
     vendor_available: true,
     host_supported: true,
-    defaults: ["libbinder_ndk_host_user"],
+    target: {
+        darwin: {
+            enabled: false,
+        },
+    },
     srcs: ["NativeHandle.cpp"],
     export_include_dirs: ["include"],
     shared_libs: [
@@ -28,7 +32,11 @@
 cc_test {
     name: "libaidlcommonsupport_test",
     host_supported: true,
-    defaults: ["libbinder_ndk_host_user"],
+    target: {
+        darwin: {
+            enabled: false,
+        },
+    },
     srcs: ["test.cpp"],
     static_libs: [
         "android.hardware.common-V2-ndk",
diff --git a/compatibility_matrices/compatibility_matrix.current.xml b/compatibility_matrices/compatibility_matrix.current.xml
index ffbcb36..6879a95 100644
--- a/compatibility_matrices/compatibility_matrix.current.xml
+++ b/compatibility_matrices/compatibility_matrix.current.xml
@@ -292,7 +292,7 @@
     </hal>
     <hal format="aidl" optional="true">
         <name>android.hardware.identity</name>
-        <version>1-3</version>
+        <version>1-4</version>
         <interface>
             <name>IIdentityCredentialStore</name>
             <instance>default</instance>
diff --git a/graphics/composer/2.1/default/OWNERS b/graphics/composer/2.1/default/OWNERS
index 709c4d1..331c80d 100644
--- a/graphics/composer/2.1/default/OWNERS
+++ b/graphics/composer/2.1/default/OWNERS
@@ -1,3 +1,4 @@
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
diff --git a/graphics/composer/2.1/utils/OWNERS b/graphics/composer/2.1/utils/OWNERS
index 7af69b4..83c4f5f 100644
--- a/graphics/composer/2.1/utils/OWNERS
+++ b/graphics/composer/2.1/utils/OWNERS
@@ -1,2 +1,3 @@
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
diff --git a/graphics/composer/2.1/vts/OWNERS b/graphics/composer/2.1/vts/OWNERS
index ea06752..a643bbd 100644
--- a/graphics/composer/2.1/vts/OWNERS
+++ b/graphics/composer/2.1/vts/OWNERS
@@ -1,5 +1,6 @@
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
 
 # VTS team
diff --git a/graphics/composer/2.1/vts/functional/OWNERS b/graphics/composer/2.1/vts/functional/OWNERS
index a2ed8c8..3d970d1 100644
--- a/graphics/composer/2.1/vts/functional/OWNERS
+++ b/graphics/composer/2.1/vts/functional/OWNERS
@@ -1,2 +1,4 @@
 # Bug component: 25423
+adyabr@google.com
+alecmouri@google.com
 sumir@google.com
diff --git a/graphics/composer/2.2/default/OWNERS b/graphics/composer/2.2/default/OWNERS
index 709c4d1..e8f584d 100644
--- a/graphics/composer/2.2/default/OWNERS
+++ b/graphics/composer/2.2/default/OWNERS
@@ -1,3 +1,5 @@
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
+
diff --git a/graphics/composer/2.2/utils/OWNERS b/graphics/composer/2.2/utils/OWNERS
index 709c4d1..331c80d 100644
--- a/graphics/composer/2.2/utils/OWNERS
+++ b/graphics/composer/2.2/utils/OWNERS
@@ -1,3 +1,4 @@
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
diff --git a/graphics/composer/2.2/vts/functional/OWNERS b/graphics/composer/2.2/vts/functional/OWNERS
index 31b0dc7..a4eb0ca 100644
--- a/graphics/composer/2.2/vts/functional/OWNERS
+++ b/graphics/composer/2.2/vts/functional/OWNERS
@@ -1,5 +1,6 @@
 # Bug component: 25423
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
 sumir@google.com
diff --git a/graphics/composer/2.3/default/OWNERS b/graphics/composer/2.3/default/OWNERS
index 709c4d1..331c80d 100644
--- a/graphics/composer/2.3/default/OWNERS
+++ b/graphics/composer/2.3/default/OWNERS
@@ -1,3 +1,4 @@
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
diff --git a/graphics/composer/2.3/utils/OWNERS b/graphics/composer/2.3/utils/OWNERS
index 709c4d1..331c80d 100644
--- a/graphics/composer/2.3/utils/OWNERS
+++ b/graphics/composer/2.3/utils/OWNERS
@@ -1,3 +1,4 @@
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
diff --git a/graphics/composer/2.3/vts/functional/OWNERS b/graphics/composer/2.3/vts/functional/OWNERS
index 31b0dc7..a4eb0ca 100644
--- a/graphics/composer/2.3/vts/functional/OWNERS
+++ b/graphics/composer/2.3/vts/functional/OWNERS
@@ -1,5 +1,6 @@
 # Bug component: 25423
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
 sumir@google.com
diff --git a/graphics/composer/2.4/default/OWNERS b/graphics/composer/2.4/default/OWNERS
index 709c4d1..331c80d 100644
--- a/graphics/composer/2.4/default/OWNERS
+++ b/graphics/composer/2.4/default/OWNERS
@@ -1,3 +1,4 @@
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
diff --git a/graphics/composer/2.4/utils/OWNERS b/graphics/composer/2.4/utils/OWNERS
index 709c4d1..331c80d 100644
--- a/graphics/composer/2.4/utils/OWNERS
+++ b/graphics/composer/2.4/utils/OWNERS
@@ -1,3 +1,4 @@
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
diff --git a/graphics/composer/2.4/vts/functional/OWNERS b/graphics/composer/2.4/vts/functional/OWNERS
index 31b0dc7..a4eb0ca 100644
--- a/graphics/composer/2.4/vts/functional/OWNERS
+++ b/graphics/composer/2.4/vts/functional/OWNERS
@@ -1,5 +1,6 @@
 # Bug component: 25423
 # Graphics team
 adyabr@google.com
+alecmouri@google.com
 lpy@google.com
 sumir@google.com
diff --git a/health/aidl/Android.bp b/health/aidl/Android.bp
index 22bb4fa..86bca69 100644
--- a/health/aidl/Android.bp
+++ b/health/aidl/Android.bp
@@ -62,9 +62,11 @@
         "android.hardware.health@2.0",
         "android.hardware.health@2.1",
     ],
-    defaults: [
-        "libbinder_ndk_host_user",
-    ],
+    target: {
+        darwin: {
+            enabled: false,
+        },
+    },
 }
 
 java_library {
diff --git a/health/utils/libhealthshim/Android.bp b/health/utils/libhealthshim/Android.bp
index 311e951..42e4ea7 100644
--- a/health/utils/libhealthshim/Android.bp
+++ b/health/utils/libhealthshim/Android.bp
@@ -24,9 +24,11 @@
 cc_defaults {
     name: "libhealthshim_defaults",
     host_supported: true, // for testing
-    defaults: [
-        "libbinder_ndk_host_user",
-    ],
+    target: {
+        darwin: {
+            enabled: false,
+        },
+    },
     cflags: [
         "-Wall",
         "-Werror",
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/Certificate.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/Certificate.aidl
index d8a8128..83e1797 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/Certificate.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/Certificate.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/CipherSuite.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/CipherSuite.aidl
index 2685525..e6ec04e 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/CipherSuite.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/CipherSuite.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/HardwareInformation.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/HardwareInformation.aidl
index f8d5a9e..cd8d56b 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/HardwareInformation.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/HardwareInformation.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IIdentityCredential.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IIdentityCredential.aidl
index 3224e4b..5065641 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IIdentityCredential.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IIdentityCredential.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IIdentityCredentialStore.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IIdentityCredentialStore.aidl
index c6fb3c8..c912c52 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IIdentityCredentialStore.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IIdentityCredentialStore.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
@@ -36,6 +37,7 @@
   android.hardware.identity.HardwareInformation getHardwareInformation();
   android.hardware.identity.IWritableIdentityCredential createCredential(in @utf8InCpp String docType, in boolean testCredential);
   android.hardware.identity.IIdentityCredential getCredential(in android.hardware.identity.CipherSuite cipherSuite, in byte[] credentialData);
+  android.hardware.identity.IPresentationSession createPresentationSession(in android.hardware.identity.CipherSuite cipherSuite);
   const int STATUS_OK = 0;
   const int STATUS_FAILED = 1;
   const int STATUS_CIPHER_SUITE_NOT_SUPPORTED = 2;
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IPresentationSession.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IPresentationSession.aidl
new file mode 100644
index 0000000..705dc29
--- /dev/null
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IPresentationSession.aidl
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+///////////////////////////////////////////////////////////////////////////////
+// THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
+///////////////////////////////////////////////////////////////////////////////
+
+// This file is a snapshot of an AIDL file. Do not edit it manually. There are
+// two cases:
+// 1). this is a frozen version file - do not edit this in any case.
+// 2). this is a 'current' file. If you make a backwards compatible change to
+//     the interface (from the latest frozen version), the build system will
+//     prompt you to update this file with `m <name>-update-api`.
+//
+// You must not make a backward incompatible change to any AIDL file built
+// with the aidl_interface module type with versions property set. The module
+// type is used to build AIDL files in a way that they can be used across
+// independently updatable components of the system. If a device is shipped
+// with such a backward incompatible change, it has a high risk of breaking
+// later when a module using the interface is updated, e.g., Mainline modules.
+
+package android.hardware.identity;
+@VintfStability
+interface IPresentationSession {
+  byte[] getEphemeralKeyPair();
+  long getAuthChallenge();
+  void setReaderEphemeralPublicKey(in byte[] publicKey);
+  void setSessionTranscript(in byte[] sessionTranscript);
+  android.hardware.identity.IIdentityCredential getCredential(in byte[] credentialData);
+}
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IWritableIdentityCredential.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IWritableIdentityCredential.aidl
index 19a29ec..9a0fa9e 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IWritableIdentityCredential.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/IWritableIdentityCredential.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/RequestDataItem.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/RequestDataItem.aidl
index c9c2b9f..cec8e0c 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/RequestDataItem.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/RequestDataItem.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/RequestNamespace.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/RequestNamespace.aidl
index aaf1e20..05b9ec2 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/RequestNamespace.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/RequestNamespace.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
diff --git a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/SecureAccessControlProfile.aidl b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/SecureAccessControlProfile.aidl
index 695fb3f..2003594 100644
--- a/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/SecureAccessControlProfile.aidl
+++ b/identity/aidl/aidl_api/android.hardware.identity/current/android/hardware/identity/SecureAccessControlProfile.aidl
@@ -12,7 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *////////////////////////////////////////////////////////////////////////////////
+ */
+///////////////////////////////////////////////////////////////////////////////
 // THIS FILE IS IMMUTABLE. DO NOT EDIT IN ANY CASE.                          //
 ///////////////////////////////////////////////////////////////////////////////
 
diff --git a/identity/aidl/android/hardware/identity/IIdentityCredential.aidl b/identity/aidl/android/hardware/identity/IIdentityCredential.aidl
index 8ae293b..84d6ed0 100644
--- a/identity/aidl/android/hardware/identity/IIdentityCredential.aidl
+++ b/identity/aidl/android/hardware/identity/IIdentityCredential.aidl
@@ -17,9 +17,9 @@
 package android.hardware.identity;
 
 import android.hardware.identity.Certificate;
+import android.hardware.identity.IWritableIdentityCredential;
 import android.hardware.identity.RequestNamespace;
 import android.hardware.identity.SecureAccessControlProfile;
-import android.hardware.identity.IWritableIdentityCredential;
 import android.hardware.keymaster.HardwareAuthToken;
 import android.hardware.keymaster.VerificationToken;
 
@@ -44,6 +44,9 @@
      * This method was deprecated in API version 3 because there's no challenge so freshness
      * can't be checked. Use deleteCredentalWithChallenge() instead.
      *
+     * If the method is called on an instance obtained via IPresentationSession.getCredential(),
+     * STATUS_FAILED must be returned.
+     *
      * @return a COSE_Sign1 signature described above
      * @deprecated use deleteCredentalWithChallenge() instead.
      */
@@ -60,6 +63,9 @@
      * This method may only be called once per instance. If called more than once, STATUS_FAILED
      * will be returned.
      *
+     * If the method is called on an instance obtained via IPresentationSession.getCredential(),
+     * STATUS_FAILED must be returned.
+     *
      * @return the private key, in DER format as specified in RFC 5915.
      */
     byte[] createEphemeralKeyPair();
@@ -70,6 +76,9 @@
      * This method may only be called once per instance. If called more than once, STATUS_FAILED
      * will be returned.
      *
+     * If the method is called on an instance obtained via IPresentationSession.getCredential(),
+     * STATUS_FAILED must be returned.
+     *
      * @param publicKey contains the reader's ephemeral public key, in uncompressed
      *        form (e.g. 0x04 || X || Y).
      */
@@ -83,6 +92,9 @@
      * This method may only be called once per instance. If called more than once, STATUS_FAILED
      * will be returned. If user authentication is not needed, this method may not be called.
      *
+     * If the method is called on an instance obtained via IPresentationSession.getCredential(),
+     * STATUS_FAILED must be returned.
+     *
      * @return challenge, a non-zero number.
      */
     long createAuthChallenge();
@@ -371,6 +383,9 @@
      * This CBOR enables an issuer to determine the exact state of the credential it
      * returns issuer-signed data for.
      *
+     * If the method is called on an instance obtained via IPresentationSession.getCredential(),
+     * STATUS_FAILED must be returned.
+     *
      * @param out signingKeyBlob contains an AES-GCM-ENC(storageKey, R, signingKey, docType)
      *     where signingKey is an EC private key in uncompressed form. That is, the returned
      *     blob is an encrypted copy of the newly-generated private signing key.
@@ -420,6 +435,9 @@
      *
      * This method was introduced in API version 3.
      *
+     * If the method is called on an instance obtained via IPresentationSession.getCredential(),
+     * STATUS_FAILED must be returned.
+     *
      * @param challenge a challenge set by the issuer to ensure freshness. Maximum size is 32 bytes
      *     and it may be empty. Fails with STATUS_INVALID_DATA if bigger than 32 bytes.
      * @return a COSE_Sign1 signature described above.
@@ -442,6 +460,9 @@
      *
      * This method was introduced in API version 3.
      *
+     * If the method is called on an instance obtained via IPresentationSession.getCredential(),
+     * STATUS_FAILED must be returned.
+     *
      * @param challenge a challenge set by the issuer to ensure freshness. Maximum size is 32 bytes
      *     and it may be empty. Fails with STATUS_INVALID_DATA if bigger than 32 bytes.
      * @return a COSE_Sign1 signature described above.
@@ -456,6 +477,9 @@
      *
      * This method was introduced in API version 3.
      *
+     * If the method is called on an instance obtained via IPresentationSession.getCredential(),
+     * STATUS_FAILED must be returned.
+     *
      * @return an IWritableIdentityCredential
      */
     IWritableIdentityCredential updateCredential();
diff --git a/identity/aidl/android/hardware/identity/IIdentityCredentialStore.aidl b/identity/aidl/android/hardware/identity/IIdentityCredentialStore.aidl
index 638be79..86be7f5 100644
--- a/identity/aidl/android/hardware/identity/IIdentityCredentialStore.aidl
+++ b/identity/aidl/android/hardware/identity/IIdentityCredentialStore.aidl
@@ -16,10 +16,11 @@
 
 package android.hardware.identity;
 
-import android.hardware.identity.IIdentityCredential;
-import android.hardware.identity.IWritableIdentityCredential;
-import android.hardware.identity.HardwareInformation;
 import android.hardware.identity.CipherSuite;
+import android.hardware.identity.HardwareInformation;
+import android.hardware.identity.IIdentityCredential;
+import android.hardware.identity.IPresentationSession;
+import android.hardware.identity.IWritableIdentityCredential;
 
 /**
  * IIdentityCredentialStore provides an interface to a secure store for user identity documents.
@@ -105,7 +106,7 @@
  * STATUS_* integers defined in this interface. Each method states which status can be returned
  * and under which circumstances.
  *
- * The API described here is API version 3 which corresponds to feature version 202101
+ * The API described here is API version 4 which corresponds to feature version 202201
  * of the android.security.identity Framework API. An XML file declaring the feature
  * android.hardware.identity_credential (or android.hardware.identity_credential.direct_access
  * if implementing the Direct Access HAL) should be included declaring this feature version.
@@ -241,4 +242,25 @@
      * @return an IIdentityCredential interface that provides operations on the Credential.
      */
     IIdentityCredential getCredential(in CipherSuite cipherSuite, in byte[] credentialData);
+
+    /**
+     * createPresentationSession creates IPresentationSession interface which can be used to
+     * present one or more credentials to a remote verifier device.
+     *
+     * The cipher suite used to communicate with the remote verifier must be specified. Currently
+     * only a single cipher-suite is supported. Support for other cipher suites may be added in a
+     * future version of this HAL. If the requested cipher suite is not support the call fails
+     * with STATUS_CIPHER_SUITE_NOT_SUPPORTED.
+     *
+     * In this version of the HAL, implementations are only required to support a single session
+     * being active. In a future version, implementations may be required to support multiple
+     * presentation sessions being active at the same time.
+     *
+     * This method was introduced in API version 4.
+     *
+     * @param cipherSuite The cipher suite to use.
+     *
+     * @return an IPresentationSession interface.
+     */
+    IPresentationSession createPresentationSession(in CipherSuite cipherSuite);
 }
diff --git a/identity/aidl/android/hardware/identity/IPresentationSession.aidl b/identity/aidl/android/hardware/identity/IPresentationSession.aidl
new file mode 100644
index 0000000..b0449f0
--- /dev/null
+++ b/identity/aidl/android/hardware/identity/IPresentationSession.aidl
@@ -0,0 +1,101 @@
+/*
+ * Copyright 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.hardware.identity;
+
+import android.hardware.identity.CipherSuite;
+import android.hardware.identity.IIdentityCredential;
+
+/**
+ * An interface to present multiple credentials in the same session.
+ *
+ * This interface was introduced in API version 4.
+ *
+ */
+@VintfStability
+interface IPresentationSession {
+    /**
+     * Gets the ephemeral EC key pair to be used in establishing a secure session with a reader.
+     * This method returns the private key so the caller can perform an ECDH key agreement operation
+     * with the reader.  The reason for generating the key pair in the secure environment is so that
+     * the secure environment knows what public key to expect to find in the session transcript
+     * when presenting credentials.
+     *
+     * The generated key matches the selected cipher suite of the presentation session (e.g. EC
+     * key using the P-256 curve).
+     *
+     * @return the private key, in DER format as specified in RFC 5915.
+     */
+    byte[] getEphemeralKeyPair();
+
+    /**
+     * Gets the challenge value to be used for proving successful user authentication. This
+     * is to be included in the authToken passed to the IIdentityCredential.startRetrieval()
+     * method and the verificationToken passed to the IIdentityCredential.setVerificationToken()
+     * method.
+     *
+     * @return challenge, a non-zero number.
+     */
+    long getAuthChallenge();
+
+    /**
+     * Sets the public part of the reader's ephemeral key pair to be used to complete
+     * an ECDH key agreement for the session.
+     *
+     * The curve of the key must match the curve for the key returned by getEphemeralKeyPair().
+     *
+     * This method may only be called once per instance. If called more than once, STATUS_FAILED
+     * must be returned.
+     *
+     * @param publicKey contains the reader's ephemeral public key, in uncompressed
+     *        form (e.g. 0x04 || X || Y).
+     */
+    void setReaderEphemeralPublicKey(in byte[] publicKey);
+
+    /**
+     * Sets the session transcript for the session.
+     *
+     * This can be empty but if it's non-empty it must be valid CBOR.
+     *
+     * This method may only be called once per instance. If called more than once, STATUS_FAILED
+     * must be returned.
+     *
+     * @param sessionTrancsript the session transcript.
+     */
+    void setSessionTranscript(in byte[] sessionTranscript);
+
+    /**
+     * getCredential() retrieves an IIdentityCredential interface for presentation in the
+     * current presentation session.
+     *
+     * On the returned instance only the methods startRetrieval(), startRetrieveEntryValue(),
+     * retrieveEntryValue(), finishRetrieval(), setRequestedNamespaces(), setVerificationToken()
+     * may be called. Other methods will fail with STATUS_FAILED.
+     *
+     * The implementation is expected to get the session transcript, ephemeral key, reader
+     * ephemeral key, and auth challenge from this instance.
+     *
+     * @param credentialData is a CBOR-encoded structure containing metadata about the credential
+     *     and an encrypted byte array that contains data used to secure the credential.  See the
+     *     return argument of the same name in IWritableIdentityCredential.finishAddingEntries().
+     *
+     *     Note that the format of credentialData may depend on the feature version.
+     *     Implementations must support credentialData created by an earlier feature version.
+     *
+     * @return an IIdentityCredential interface that provides operations on the Credential.
+     */
+    IIdentityCredential getCredential(in byte[] credentialData);
+}
diff --git a/identity/aidl/default/Android.bp b/identity/aidl/default/Android.bp
index 3de8d30..ca24afa 100644
--- a/identity/aidl/default/Android.bp
+++ b/identity/aidl/default/Android.bp
@@ -13,6 +13,7 @@
     srcs: [
         "common/IdentityCredential.cpp",
         "common/IdentityCredentialStore.cpp",
+        "common/PresentationSession.cpp",
         "common/WritableIdentityCredential.cpp",
     ],
     export_include_dirs: [
@@ -39,8 +40,8 @@
         "libsoft_attestation_cert",
         "libpuresoftkeymasterdevice",
         "android.hardware.identity-support-lib",
-        "android.hardware.identity-V3-ndk",
-        "android.hardware.keymaster-V3-ndk",
+        "android.hardware.identity-V4-ndk",
+        "android.hardware.keymaster-V4-ndk",
     ],
 }
 
@@ -49,6 +50,7 @@
     vendor_available: true,
     srcs: [
         "libeic/EicCbor.c",
+        "libeic/EicSession.c",
         "libeic/EicPresentation.c",
         "libeic/EicProvisioning.c",
         "EicOpsImpl.cc",
@@ -100,8 +102,8 @@
         "libsoft_attestation_cert",
         "libpuresoftkeymasterdevice",
         "android.hardware.identity-support-lib",
-        "android.hardware.identity-V3-ndk",
-        "android.hardware.keymaster-V3-ndk",
+        "android.hardware.identity-V4-ndk",
+        "android.hardware.keymaster-V4-ndk",
         "android.hardware.identity-libeic-hal-common",
         "android.hardware.identity-libeic-library",
     ],
diff --git a/identity/aidl/default/EicOpsImpl.cc b/identity/aidl/default/EicOpsImpl.cc
index 8ec4cc9..c98a91e 100644
--- a/identity/aidl/default/EicOpsImpl.cc
+++ b/identity/aidl/default/EicOpsImpl.cc
@@ -20,9 +20,13 @@
 #include <tuple>
 #include <vector>
 
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <string.h>
+
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
-#include <string.h>
 
 #include <android/hardware/identity/support/IdentityCredentialSupport.h>
 
@@ -63,6 +67,11 @@
     return strlen(s);
 }
 
+void* eicMemMem(const uint8_t* haystack, size_t haystackLen, const uint8_t* needle,
+                size_t needleLen) {
+    return memmem(haystack, haystackLen, needle, needleLen);
+}
+
 int eicCryptoMemCmp(const void* s1, const void* s2, size_t n) {
     return CRYPTO_memcmp(s1, s2, n);
 }
@@ -117,6 +126,25 @@
     return true;
 }
 
+bool eicNextId(uint32_t* id) {
+    uint32_t oldId = *id;
+    uint32_t newId = 0;
+
+    do {
+        union {
+            uint8_t value8;
+            uint32_t value32;
+        } value;
+        if (!eicOpsRandom(&value.value8, sizeof(value))) {
+            return false;
+        }
+        newId = value.value32;
+    } while (newId == oldId && newId == 0);
+
+    *id = newId;
+    return true;
+}
+
 bool eicOpsEncryptAes128Gcm(
         const uint8_t* key,    // Must be 16 bytes
         const uint8_t* nonce,  // Must be 12 bytes
diff --git a/identity/aidl/default/EicTests.cpp b/identity/aidl/default/EicTests.cpp
index a28080d..7b69b75 100644
--- a/identity/aidl/default/EicTests.cpp
+++ b/identity/aidl/default/EicTests.cpp
@@ -66,7 +66,8 @@
     // Then present data from it...
     //
     FakeSecureHardwarePresentationProxy presentationProxy;
-    ASSERT_TRUE(presentationProxy.initialize(isTestCredential, docType, credData.value()));
+    ASSERT_TRUE(presentationProxy.initialize(0 /* sessionId */, isTestCredential, docType,
+                                             credData.value()));
     AccessCheckResult res =
             presentationProxy.startRetrieveEntryValue(nameSpace, name, 1, content.size(), acpIds);
     ASSERT_EQ(res, AccessCheckResult::kNoAccessControlProfiles);
diff --git a/identity/aidl/default/FakeSecureHardwareProxy.cpp b/identity/aidl/default/FakeSecureHardwareProxy.cpp
index f0307dc..91e634c 100644
--- a/identity/aidl/default/FakeSecureHardwareProxy.cpp
+++ b/identity/aidl/default/FakeSecureHardwareProxy.cpp
@@ -23,6 +23,7 @@
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
 #include <string.h>
+#include <map>
 
 #include <openssl/sha.h>
 
@@ -52,38 +53,110 @@
 
 // ----------------------------------------------------------------------
 
-FakeSecureHardwareProvisioningProxy::FakeSecureHardwareProvisioningProxy() {}
+// The singleton EicProvisioning object used everywhere.
+//
+EicProvisioning FakeSecureHardwareProvisioningProxy::ctx_;
 
-FakeSecureHardwareProvisioningProxy::~FakeSecureHardwareProvisioningProxy() {}
-
-bool FakeSecureHardwareProvisioningProxy::shutdown() {
-    LOG(INFO) << "FakeSecureHardwarePresentationProxy shutdown";
-    return true;
+FakeSecureHardwareProvisioningProxy::~FakeSecureHardwareProvisioningProxy() {
+    if (id_ != 0) {
+        shutdown();
+    }
 }
 
 bool FakeSecureHardwareProvisioningProxy::initialize(bool testCredential) {
-    LOG(INFO) << "FakeSecureHardwareProvisioningProxy created, sizeof(EicProvisioning): "
-              << sizeof(EicProvisioning);
-    return eicProvisioningInit(&ctx_, testCredential);
+    if (id_ != 0) {
+        LOG(WARNING) << "Proxy is already initialized";
+        return false;
+    }
+    bool initialized = eicProvisioningInit(&ctx_, testCredential);
+    if (!initialized) {
+        return false;
+    }
+    optional<uint32_t> id = getId();
+    if (!id) {
+        LOG(WARNING) << "Error getting id";
+        return false;
+    }
+    id_ = id.value();
+    return true;
 }
 
 bool FakeSecureHardwareProvisioningProxy::initializeForUpdate(
-        bool testCredential, string docType, vector<uint8_t> encryptedCredentialKeys) {
-    return eicProvisioningInitForUpdate(&ctx_, testCredential, docType.c_str(),
-                                        docType.size(),
-                                        encryptedCredentialKeys.data(),
-                                        encryptedCredentialKeys.size());
+        bool testCredential, const string& docType,
+        const vector<uint8_t>& encryptedCredentialKeys) {
+    if (id_ != 0) {
+        LOG(WARNING) << "Proxy is already initialized";
+        return false;
+    }
+    bool initialized = eicProvisioningInitForUpdate(&ctx_, testCredential, docType.c_str(),
+                                                    docType.size(), encryptedCredentialKeys.data(),
+                                                    encryptedCredentialKeys.size());
+    if (!initialized) {
+        return false;
+    }
+    optional<uint32_t> id = getId();
+    if (!id) {
+        LOG(WARNING) << "Error getting id";
+        return false;
+    }
+    id_ = id.value();
+    return true;
+}
+
+optional<uint32_t> FakeSecureHardwareProvisioningProxy::getId() {
+    uint32_t id;
+    if (!eicProvisioningGetId(&ctx_, &id)) {
+        return std::nullopt;
+    }
+    return id;
+}
+
+bool FakeSecureHardwareProvisioningProxy::validateId(const string& callerName) {
+    if (id_ == 0) {
+        LOG(WARNING) << "FakeSecureHardwareProvisioningProxy::" << callerName
+                     << ": While validating expected id is 0";
+        return false;
+    }
+    optional<uint32_t> id = getId();
+    if (!id) {
+        LOG(WARNING) << "FakeSecureHardwareProvisioningProxy::" << callerName
+                     << ": Error getting id for validating";
+        return false;
+    }
+    if (id.value() != id_) {
+        LOG(WARNING) << "FakeSecureHardwareProvisioningProxy::" << callerName
+                     << ": While validating expected id " << id_ << " but got " << id.value();
+        return false;
+    }
+    return true;
+}
+
+bool FakeSecureHardwareProvisioningProxy::shutdown() {
+    bool validated = validateId(__func__);
+    id_ = 0;
+    if (!validated) {
+        return false;
+    }
+    if (!eicProvisioningShutdown(&ctx_)) {
+        LOG(INFO) << "Error shutting down provisioning";
+        return false;
+    }
+    return true;
 }
 
 // Returns public key certificate.
 optional<vector<uint8_t>> FakeSecureHardwareProvisioningProxy::createCredentialKey(
         const vector<uint8_t>& challenge, const vector<uint8_t>& applicationId) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     uint8_t publicKeyCert[4096];
     size_t publicKeyCertSize = sizeof publicKeyCert;
     if (!eicProvisioningCreateCredentialKey(&ctx_, challenge.data(), challenge.size(),
                                             applicationId.data(), applicationId.size(),
                                             publicKeyCert, &publicKeyCertSize)) {
-        return {};
+        return std::nullopt;
     }
     vector<uint8_t> pubKeyCert(publicKeyCertSize);
     memcpy(pubKeyCert.data(), publicKeyCert, publicKeyCertSize);
@@ -91,8 +164,11 @@
 }
 
 bool FakeSecureHardwareProvisioningProxy::startPersonalization(
-        int accessControlProfileCount, vector<int> entryCounts, const string& docType,
+        int accessControlProfileCount, const vector<int>& entryCounts, const string& docType,
         size_t expectedProofOfProvisioningSize) {
+    if (!validateId(__func__)) {
+        return false;
+    }
 
     if (!eicProvisioningStartPersonalization(&ctx_, accessControlProfileCount,
                                              entryCounts.data(),
@@ -108,13 +184,17 @@
 optional<vector<uint8_t>> FakeSecureHardwareProvisioningProxy::addAccessControlProfile(
         int id, const vector<uint8_t>& readerCertificate, bool userAuthenticationRequired,
         uint64_t timeoutMillis, uint64_t secureUserId) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     vector<uint8_t> mac(28);
     uint8_t scratchSpace[512];
     if (!eicProvisioningAddAccessControlProfile(
                 &ctx_, id, readerCertificate.data(), readerCertificate.size(),
                 userAuthenticationRequired, timeoutMillis, secureUserId, mac.data(),
                 scratchSpace, sizeof(scratchSpace))) {
-        return {};
+        return std::nullopt;
     }
     return mac;
 }
@@ -122,6 +202,10 @@
 bool FakeSecureHardwareProvisioningProxy::beginAddEntry(const vector<int>& accessControlProfileIds,
                                                         const string& nameSpace, const string& name,
                                                         uint64_t entrySize) {
+    if (!validateId(__func__)) {
+        return false;
+    }
+
     uint8_t scratchSpace[512];
     vector<uint8_t> uint8AccessControlProfileIds;
     for (size_t i = 0; i < accessControlProfileIds.size(); i++) {
@@ -138,6 +222,10 @@
 optional<vector<uint8_t>> FakeSecureHardwareProvisioningProxy::addEntryValue(
         const vector<int>& accessControlProfileIds, const string& nameSpace, const string& name,
         const vector<uint8_t>& content) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     vector<uint8_t> eicEncryptedContent;
     uint8_t scratchSpace[512];
     vector<uint8_t> uint8AccessControlProfileIds;
@@ -150,16 +238,20 @@
                 &ctx_, uint8AccessControlProfileIds.data(), uint8AccessControlProfileIds.size(),
                 nameSpace.c_str(), nameSpace.size(), name.c_str(), name.size(), content.data(),
                 content.size(), eicEncryptedContent.data(), scratchSpace, sizeof(scratchSpace))) {
-        return {};
+        return std::nullopt;
     }
     return eicEncryptedContent;
 }
 
 // Returns signatureOfToBeSigned (EIC_ECDSA_P256_SIGNATURE_SIZE bytes).
 optional<vector<uint8_t>> FakeSecureHardwareProvisioningProxy::finishAddingEntries() {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     vector<uint8_t> signatureOfToBeSigned(EIC_ECDSA_P256_SIGNATURE_SIZE);
     if (!eicProvisioningFinishAddingEntries(&ctx_, signatureOfToBeSigned.data())) {
-        return {};
+        return std::nullopt;
     }
     return signatureOfToBeSigned;
 }
@@ -167,11 +259,15 @@
 // Returns encryptedCredentialKeys.
 optional<vector<uint8_t>> FakeSecureHardwareProvisioningProxy::finishGetCredentialData(
         const string& docType) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     vector<uint8_t> encryptedCredentialKeys(116);
     size_t size = encryptedCredentialKeys.size();
     if (!eicProvisioningFinishGetCredentialData(&ctx_, docType.c_str(), docType.size(),
                                                 encryptedCredentialKeys.data(), &size)) {
-        return {};
+        return std::nullopt;
     }
     encryptedCredentialKeys.resize(size);
     return encryptedCredentialKeys;
@@ -179,21 +275,200 @@
 
 // ----------------------------------------------------------------------
 
-FakeSecureHardwarePresentationProxy::FakeSecureHardwarePresentationProxy() {}
+// The singleton EicSession object used everywhere.
+//
+EicSession FakeSecureHardwareSessionProxy::ctx_;
 
-FakeSecureHardwarePresentationProxy::~FakeSecureHardwarePresentationProxy() {}
+FakeSecureHardwareSessionProxy::~FakeSecureHardwareSessionProxy() {
+    if (id_ != 0) {
+        shutdown();
+    }
+}
 
-bool FakeSecureHardwarePresentationProxy::initialize(bool testCredential, string docType,
-                                                     vector<uint8_t> encryptedCredentialKeys) {
-    LOG(INFO) << "FakeSecureHardwarePresentationProxy created, sizeof(EicPresentation): "
-              << sizeof(EicPresentation);
-    return eicPresentationInit(&ctx_, testCredential, docType.c_str(), docType.size(),
-                               encryptedCredentialKeys.data(), encryptedCredentialKeys.size());
+bool FakeSecureHardwareSessionProxy::initialize() {
+    if (id_ != 0) {
+        LOG(WARNING) << "Proxy is already initialized";
+        return false;
+    }
+    bool initialized = eicSessionInit(&ctx_);
+    if (!initialized) {
+        return false;
+    }
+    optional<uint32_t> id = getId();
+    if (!id) {
+        LOG(WARNING) << "Error getting id";
+        return false;
+    }
+    id_ = id.value();
+    return true;
+}
+
+optional<uint32_t> FakeSecureHardwareSessionProxy::getId() {
+    uint32_t id;
+    if (!eicSessionGetId(&ctx_, &id)) {
+        return std::nullopt;
+    }
+    return id;
+}
+
+bool FakeSecureHardwareSessionProxy::shutdown() {
+    bool validated = validateId(__func__);
+    id_ = 0;
+    if (!validated) {
+        return false;
+    }
+    if (!eicSessionShutdown(&ctx_)) {
+        LOG(INFO) << "Error shutting down session";
+        return false;
+    }
+    return true;
+}
+
+bool FakeSecureHardwareSessionProxy::validateId(const string& callerName) {
+    if (id_ == 0) {
+        LOG(WARNING) << "FakeSecureHardwareSessionProxy::" << callerName
+                     << ": While validating expected id is 0";
+        return false;
+    }
+    optional<uint32_t> id = getId();
+    if (!id) {
+        LOG(WARNING) << "FakeSecureHardwareSessionProxy::" << callerName
+                     << ": Error getting id for validating";
+        return false;
+    }
+    if (id.value() != id_) {
+        LOG(WARNING) << "FakeSecureHardwareSessionProxy::" << callerName
+                     << ": While validating expected id " << id_ << " but got " << id.value();
+        return false;
+    }
+    return true;
+}
+
+optional<uint64_t> FakeSecureHardwareSessionProxy::getAuthChallenge() {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
+    uint64_t authChallenge;
+    if (!eicSessionGetAuthChallenge(&ctx_, &authChallenge)) {
+        return std::nullopt;
+    }
+    return authChallenge;
+}
+
+optional<vector<uint8_t>> FakeSecureHardwareSessionProxy::getEphemeralKeyPair() {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
+    vector<uint8_t> priv(EIC_P256_PRIV_KEY_SIZE);
+    if (!eicSessionGetEphemeralKeyPair(&ctx_, priv.data())) {
+        return std::nullopt;
+    }
+    return priv;
+}
+
+bool FakeSecureHardwareSessionProxy::setReaderEphemeralPublicKey(
+        const vector<uint8_t>& readerEphemeralPublicKey) {
+    if (!validateId(__func__)) {
+        return false;
+    }
+
+    return eicSessionSetReaderEphemeralPublicKey(&ctx_, readerEphemeralPublicKey.data());
+}
+
+bool FakeSecureHardwareSessionProxy::setSessionTranscript(
+        const vector<uint8_t>& sessionTranscript) {
+    if (!validateId(__func__)) {
+        return false;
+    }
+
+    return eicSessionSetSessionTranscript(&ctx_, sessionTranscript.data(),
+                                          sessionTranscript.size());
+}
+
+// ----------------------------------------------------------------------
+
+// The singleton EicPresentation object used everywhere.
+//
+EicPresentation FakeSecureHardwarePresentationProxy::ctx_;
+
+FakeSecureHardwarePresentationProxy::~FakeSecureHardwarePresentationProxy() {
+    if (id_ != 0) {
+        shutdown();
+    }
+}
+
+bool FakeSecureHardwarePresentationProxy::initialize(
+        uint32_t sessionId, bool testCredential, const string& docType,
+        const vector<uint8_t>& encryptedCredentialKeys) {
+    if (id_ != 0) {
+        LOG(WARNING) << "Proxy is already initialized";
+        return false;
+    }
+    bool initialized =
+            eicPresentationInit(&ctx_, sessionId, testCredential, docType.c_str(), docType.size(),
+                                encryptedCredentialKeys.data(), encryptedCredentialKeys.size());
+    if (!initialized) {
+        return false;
+    }
+    optional<uint32_t> id = getId();
+    if (!id) {
+        LOG(WARNING) << "Error getting id";
+        return false;
+    }
+    id_ = id.value();
+    return true;
+}
+
+optional<uint32_t> FakeSecureHardwarePresentationProxy::getId() {
+    uint32_t id;
+    if (!eicPresentationGetId(&ctx_, &id)) {
+        return std::nullopt;
+    }
+    return id;
+}
+
+bool FakeSecureHardwarePresentationProxy::validateId(const string& callerName) {
+    if (id_ == 0) {
+        LOG(WARNING) << "FakeSecureHardwarePresentationProxy::" << callerName
+                     << ": While validating expected id is 0";
+        return false;
+    }
+    optional<uint32_t> id = getId();
+    if (!id) {
+        LOG(WARNING) << "FakeSecureHardwarePresentationProxy::" << callerName
+                     << ": Error getting id for validating";
+        return false;
+    }
+    if (id.value() != id_) {
+        LOG(WARNING) << "FakeSecureHardwarePresentationProxy::" << callerName
+                     << ": While validating expected id " << id_ << " but got " << id.value();
+        return false;
+    }
+    return true;
+}
+
+bool FakeSecureHardwarePresentationProxy::shutdown() {
+    bool validated = validateId(__func__);
+    id_ = 0;
+    if (!validated) {
+        return false;
+    }
+    if (!eicPresentationShutdown(&ctx_)) {
+        LOG(INFO) << "Error shutting down presentation";
+        return false;
+    }
+    return true;
 }
 
 // Returns publicKeyCert (1st component) and signingKeyBlob (2nd component)
 optional<pair<vector<uint8_t>, vector<uint8_t>>>
-FakeSecureHardwarePresentationProxy::generateSigningKeyPair(string docType, time_t now) {
+FakeSecureHardwarePresentationProxy::generateSigningKeyPair(const string& docType, time_t now) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     uint8_t publicKeyCert[512];
     size_t publicKeyCertSize = sizeof(publicKeyCert);
     vector<uint8_t> signingKeyBlob(60);
@@ -201,7 +476,7 @@
     if (!eicPresentationGenerateSigningKeyPair(&ctx_, docType.c_str(), docType.size(), now,
                                                publicKeyCert, &publicKeyCertSize,
                                                signingKeyBlob.data())) {
-        return {};
+        return std::nullopt;
     }
 
     vector<uint8_t> cert;
@@ -213,33 +488,44 @@
 
 // Returns private key
 optional<vector<uint8_t>> FakeSecureHardwarePresentationProxy::createEphemeralKeyPair() {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     vector<uint8_t> priv(EIC_P256_PRIV_KEY_SIZE);
     if (!eicPresentationCreateEphemeralKeyPair(&ctx_, priv.data())) {
-        return {};
+        return std::nullopt;
     }
     return priv;
 }
 
 optional<uint64_t> FakeSecureHardwarePresentationProxy::createAuthChallenge() {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     uint64_t challenge;
     if (!eicPresentationCreateAuthChallenge(&ctx_, &challenge)) {
-        return {};
+        return std::nullopt;
     }
     return challenge;
 }
 
-bool FakeSecureHardwarePresentationProxy::shutdown() {
-    LOG(INFO) << "FakeSecureHardwarePresentationProxy shutdown";
-    return true;
-}
-
 bool FakeSecureHardwarePresentationProxy::pushReaderCert(const vector<uint8_t>& certX509) {
+    if (!validateId(__func__)) {
+        return false;
+    }
+
     return eicPresentationPushReaderCert(&ctx_, certX509.data(), certX509.size());
 }
 
 bool FakeSecureHardwarePresentationProxy::validateRequestMessage(
         const vector<uint8_t>& sessionTranscript, const vector<uint8_t>& requestMessage,
         int coseSignAlg, const vector<uint8_t>& readerSignatureOfToBeSigned) {
+    if (!validateId(__func__)) {
+        return false;
+    }
+
     return eicPresentationValidateRequestMessage(
             &ctx_, sessionTranscript.data(), sessionTranscript.size(), requestMessage.data(),
             requestMessage.size(), coseSignAlg, readerSignatureOfToBeSigned.data(),
@@ -251,6 +537,10 @@
         int hardwareAuthenticatorType, uint64_t timeStamp, const vector<uint8_t>& mac,
         uint64_t verificationTokenChallenge, uint64_t verificationTokenTimestamp,
         int verificationTokenSecurityLevel, const vector<uint8_t>& verificationTokenMac) {
+    if (!validateId(__func__)) {
+        return false;
+    }
+
     return eicPresentationSetAuthToken(&ctx_, challenge, secureUserId, authenticatorId,
                                        hardwareAuthenticatorType, timeStamp, mac.data(), mac.size(),
                                        verificationTokenChallenge, verificationTokenTimestamp,
@@ -261,6 +551,10 @@
 optional<bool> FakeSecureHardwarePresentationProxy::validateAccessControlProfile(
         int id, const vector<uint8_t>& readerCertificate, bool userAuthenticationRequired,
         int timeoutMillis, uint64_t secureUserId, const vector<uint8_t>& mac) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     bool accessGranted = false;
     uint8_t scratchSpace[512];
     if (!eicPresentationValidateAccessControlProfile(&ctx_, id, readerCertificate.data(),
@@ -268,12 +562,16 @@
                                                      userAuthenticationRequired, timeoutMillis,
                                                      secureUserId, mac.data(), &accessGranted,
                                                      scratchSpace, sizeof(scratchSpace))) {
-        return {};
+        return std::nullopt;
     }
     return accessGranted;
 }
 
 bool FakeSecureHardwarePresentationProxy::startRetrieveEntries() {
+    if (!validateId(__func__)) {
+        return false;
+    }
+
     return eicPresentationStartRetrieveEntries(&ctx_);
 }
 
@@ -281,6 +579,10 @@
         const vector<uint8_t>& sessionTranscript, const vector<uint8_t>& readerEphemeralPublicKey,
         const vector<uint8_t>& signingKeyBlob, const string& docType,
         unsigned int numNamespacesWithValues, size_t expectedProofOfProvisioningSize) {
+    if (!validateId(__func__)) {
+        return false;
+    }
+
     if (signingKeyBlob.size() != 60) {
         eicDebug("Unexpected size %zd of signingKeyBlob, expected 60", signingKeyBlob.size());
         return false;
@@ -294,6 +596,10 @@
 AccessCheckResult FakeSecureHardwarePresentationProxy::startRetrieveEntryValue(
         const string& nameSpace, const string& name, unsigned int newNamespaceNumEntries,
         int32_t entrySize, const vector<int32_t>& accessControlProfileIds) {
+    if (!validateId(__func__)) {
+        return AccessCheckResult::kFailed;
+    }
+
     uint8_t scratchSpace[512];
     vector<uint8_t> uint8AccessControlProfileIds;
     for (size_t i = 0; i < accessControlProfileIds.size(); i++) {
@@ -324,6 +630,10 @@
 optional<vector<uint8_t>> FakeSecureHardwarePresentationProxy::retrieveEntryValue(
         const vector<uint8_t>& encryptedContent, const string& nameSpace, const string& name,
         const vector<int32_t>& accessControlProfileIds) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     uint8_t scratchSpace[512];
     vector<uint8_t> uint8AccessControlProfileIds;
     for (size_t i = 0; i < accessControlProfileIds.size(); i++) {
@@ -337,16 +647,20 @@
                 nameSpace.c_str(), nameSpace.size(), name.c_str(), name.size(),
                 uint8AccessControlProfileIds.data(), uint8AccessControlProfileIds.size(),
                 scratchSpace, sizeof(scratchSpace))) {
-        return {};
+        return std::nullopt;
     }
     return content;
 }
 
 optional<vector<uint8_t>> FakeSecureHardwarePresentationProxy::finishRetrieval() {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     vector<uint8_t> mac(32);
     size_t macSize = 32;
     if (!eicPresentationFinishRetrieval(&ctx_, mac.data(), &macSize)) {
-        return {};
+        return std::nullopt;
     }
     mac.resize(macSize);
     return mac;
@@ -355,11 +669,15 @@
 optional<vector<uint8_t>> FakeSecureHardwarePresentationProxy::deleteCredential(
         const string& docType, const vector<uint8_t>& challenge, bool includeChallenge,
         size_t proofOfDeletionCborSize) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     vector<uint8_t> signatureOfToBeSigned(EIC_ECDSA_P256_SIGNATURE_SIZE);
     if (!eicPresentationDeleteCredential(&ctx_, docType.c_str(), docType.size(), challenge.data(),
                                          challenge.size(), includeChallenge,
                                          proofOfDeletionCborSize, signatureOfToBeSigned.data())) {
-        return {};
+        return std::nullopt;
     }
     return signatureOfToBeSigned;
 }
@@ -367,11 +685,15 @@
 optional<vector<uint8_t>> FakeSecureHardwarePresentationProxy::proveOwnership(
         const string& docType, bool testCredential, const vector<uint8_t>& challenge,
         size_t proofOfOwnershipCborSize) {
+    if (!validateId(__func__)) {
+        return std::nullopt;
+    }
+
     vector<uint8_t> signatureOfToBeSigned(EIC_ECDSA_P256_SIGNATURE_SIZE);
     if (!eicPresentationProveOwnership(&ctx_, docType.c_str(), docType.size(), testCredential,
                                        challenge.data(), challenge.size(), proofOfOwnershipCborSize,
                                        signatureOfToBeSigned.data())) {
-        return {};
+        return std::nullopt;
     }
     return signatureOfToBeSigned;
 }
diff --git a/identity/aidl/default/FakeSecureHardwareProxy.h b/identity/aidl/default/FakeSecureHardwareProxy.h
index 6852c1a..df98c7a 100644
--- a/identity/aidl/default/FakeSecureHardwareProxy.h
+++ b/identity/aidl/default/FakeSecureHardwareProxy.h
@@ -27,21 +27,23 @@
 //
 class FakeSecureHardwareProvisioningProxy : public SecureHardwareProvisioningProxy {
   public:
-    FakeSecureHardwareProvisioningProxy();
+    FakeSecureHardwareProvisioningProxy() = default;
     virtual ~FakeSecureHardwareProvisioningProxy();
 
     bool initialize(bool testCredential) override;
 
-    bool initializeForUpdate(bool testCredential, string docType,
-                             vector<uint8_t> encryptedCredentialKeys) override;
+    bool initializeForUpdate(bool testCredential, const string& docType,
+                             const vector<uint8_t>& encryptedCredentialKeys) override;
 
     bool shutdown() override;
 
+    optional<uint32_t> getId() override;
+
     // Returns public key certificate.
     optional<vector<uint8_t>> createCredentialKey(const vector<uint8_t>& challenge,
                                                   const vector<uint8_t>& applicationId) override;
 
-    bool startPersonalization(int accessControlProfileCount, vector<int> entryCounts,
+    bool startPersonalization(int accessControlProfileCount, const vector<int>& entryCounts,
                               const string& docType,
                               size_t expectedProofOfProvisioningSize) override;
 
@@ -67,21 +69,81 @@
     optional<vector<uint8_t>> finishGetCredentialData(const string& docType) override;
 
   protected:
-    EicProvisioning ctx_;
+    // See docs for id_.
+    //
+    bool validateId(const string& callerName);
+
+    // We use a singleton libeic object, shared by all proxy instances.  This is to
+    // properly simulate a situation where libeic is used on constrained hardware
+    // with only enough RAM for a single instance of the libeic object.
+    //
+    static EicProvisioning ctx_;
+
+    // On the HAL side we keep track of the ID that was assigned to the libeic object
+    // created in secure hardware. For every call into libeic we validate that this
+    // identifier matches what is on the secure side. This is what the validateId()
+    // method does.
+    //
+    uint32_t id_ = 0;
+};
+
+// This implementation uses libEmbeddedIC in-process.
+//
+class FakeSecureHardwareSessionProxy : public SecureHardwareSessionProxy {
+  public:
+    FakeSecureHardwareSessionProxy() = default;
+    virtual ~FakeSecureHardwareSessionProxy();
+
+    bool initialize() override;
+
+    bool shutdown() override;
+
+    optional<uint32_t> getId() override;
+
+    optional<uint64_t> getAuthChallenge() override;
+
+    // Returns private key
+    optional<vector<uint8_t>> getEphemeralKeyPair() override;
+
+    bool setReaderEphemeralPublicKey(const vector<uint8_t>& readerEphemeralPublicKey) override;
+
+    bool setSessionTranscript(const vector<uint8_t>& sessionTranscript) override;
+
+  protected:
+    // See docs for id_.
+    //
+    bool validateId(const string& callerName);
+
+    // We use a singleton libeic object, shared by all proxy instances.  This is to
+    // properly simulate a situation where libeic is used on constrained hardware
+    // with only enough RAM for a single instance of the libeic object.
+    //
+    static EicSession ctx_;
+
+    // On the HAL side we keep track of the ID that was assigned to the libeic object
+    // created in secure hardware. For every call into libeic we validate that this
+    // identifier matches what is on the secure side. This is what the validateId()
+    // method does.
+    //
+    uint32_t id_ = 0;
 };
 
 // This implementation uses libEmbeddedIC in-process.
 //
 class FakeSecureHardwarePresentationProxy : public SecureHardwarePresentationProxy {
   public:
-    FakeSecureHardwarePresentationProxy();
+    FakeSecureHardwarePresentationProxy() = default;
     virtual ~FakeSecureHardwarePresentationProxy();
 
-    bool initialize(bool testCredential, string docType,
-                    vector<uint8_t> encryptedCredentialKeys) override;
+    bool initialize(uint32_t sessionId, bool testCredential, const string& docType,
+                    const vector<uint8_t>& encryptedCredentialKeys) override;
+
+    bool shutdown() override;
+
+    optional<uint32_t> getId() override;
 
     // Returns publicKeyCert (1st component) and signingKeyBlob (2nd component)
-    optional<pair<vector<uint8_t>, vector<uint8_t>>> generateSigningKeyPair(string docType,
+    optional<pair<vector<uint8_t>, vector<uint8_t>>> generateSigningKeyPair(const string& docType,
                                                                             time_t now) override;
 
     // Returns private key
@@ -133,10 +195,23 @@
                                              const vector<uint8_t>& challenge,
                                              size_t proofOfOwnershipCborSize) override;
 
-    bool shutdown() override;
-
   protected:
-    EicPresentation ctx_;
+    // See docs for id_.
+    //
+    bool validateId(const string& callerName);
+
+    // We use a singleton libeic object, shared by all proxy instances.  This is to
+    // properly simulate a situation where libeic is used on constrained hardware
+    // with only enough RAM for a single instance of the libeic object.
+    //
+    static EicPresentation ctx_;
+
+    // On the HAL side we keep track of the ID that was assigned to the libeic object
+    // created in secure hardware. For every call into libeic we validate that this
+    // identifier matches what is on the secure side. This is what the validateId()
+    // method does.
+    //
+    uint32_t id_ = 0;
 };
 
 // Factory implementation.
@@ -150,6 +225,10 @@
         return new FakeSecureHardwareProvisioningProxy();
     }
 
+    sp<SecureHardwareSessionProxy> createSessionProxy() override {
+        return new FakeSecureHardwareSessionProxy();
+    }
+
     sp<SecureHardwarePresentationProxy> createPresentationProxy() override {
         return new FakeSecureHardwarePresentationProxy();
     }
diff --git a/identity/aidl/default/android.hardware.identity_credential.xml b/identity/aidl/default/android.hardware.identity_credential.xml
index 5149792..20b2710 100644
--- a/identity/aidl/default/android.hardware.identity_credential.xml
+++ b/identity/aidl/default/android.hardware.identity_credential.xml
@@ -14,5 +14,5 @@
      limitations under the License.
 -->
 <permissions>
-  <feature name="android.hardware.identity_credential" version="202101" />
+  <feature name="android.hardware.identity_credential" version="202201" />
 </permissions>
diff --git a/identity/aidl/default/common/IdentityCredential.cpp b/identity/aidl/default/common/IdentityCredential.cpp
index 95557b5..7678ecb 100644
--- a/identity/aidl/default/common/IdentityCredential.cpp
+++ b/identity/aidl/default/common/IdentityCredential.cpp
@@ -72,14 +72,38 @@
     testCredential_ = testCredentialItem->value();
 
     encryptedCredentialKeys_ = encryptedCredentialKeysItem->value();
-    if (!hwProxy_->initialize(testCredential_, docType_, encryptedCredentialKeys_)) {
-        LOG(ERROR) << "hwProxy->initialize failed";
-        return false;
+
+    // If in a session, delay the initialization of the proxy.
+    //
+    if (!session_) {
+        ndk::ScopedAStatus status = ensureHwProxy();
+        if (!status.isOk()) {
+            LOG(ERROR) << "Error initializing hw proxy";
+            return IIdentityCredentialStore::STATUS_FAILED;
+        }
     }
 
     return IIdentityCredentialStore::STATUS_OK;
 }
 
+ndk::ScopedAStatus IdentityCredential::ensureHwProxy() {
+    if (hwProxy_) {
+        return ndk::ScopedAStatus::ok();
+    }
+    hwProxy_ = hwProxyFactory_->createPresentationProxy();
+    if (!hwProxy_) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error creating hw proxy"));
+    }
+    uint64_t sessionId = session_ ? session_->getSessionId() : EIC_PRESENTATION_ID_UNSET;
+    if (!hwProxy_->initialize(sessionId, testCredential_, docType_, encryptedCredentialKeys_)) {
+        hwProxy_.clear();
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error initializing hw proxy"));
+    }
+    return ndk::ScopedAStatus::ok();
+}
+
 ndk::ScopedAStatus IdentityCredential::deleteCredential(
         vector<uint8_t>* outProofOfDeletionSignature) {
     return deleteCredentialCommon({}, false, outProofOfDeletionSignature);
@@ -93,6 +117,14 @@
 ndk::ScopedAStatus IdentityCredential::deleteCredentialCommon(
         const vector<uint8_t>& challenge, bool includeChallenge,
         vector<uint8_t>* outProofOfDeletionSignature) {
+    if (session_) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Cannot be called in a session"));
+    }
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
+    }
     if (challenge.size() > 32) {
         return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
                 IIdentityCredentialStore::STATUS_INVALID_DATA, "Challenge too big"));
@@ -128,6 +160,14 @@
 
 ndk::ScopedAStatus IdentityCredential::proveOwnership(
         const vector<uint8_t>& challenge, vector<uint8_t>* outProofOfOwnershipSignature) {
+    if (session_) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Cannot be called in a session"));
+    }
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
+    }
     if (challenge.size() > 32) {
         return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
                 IIdentityCredentialStore::STATUS_INVALID_DATA, "Challenge too big"));
@@ -159,6 +199,14 @@
 }
 
 ndk::ScopedAStatus IdentityCredential::createEphemeralKeyPair(vector<uint8_t>* outKeyPair) {
+    if (session_) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Cannot be called in a session"));
+    }
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
+    }
     optional<vector<uint8_t>> ephemeralPriv = hwProxy_->createEphemeralKeyPair();
     if (!ephemeralPriv) {
         return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
@@ -186,11 +234,23 @@
 
 ndk::ScopedAStatus IdentityCredential::setReaderEphemeralPublicKey(
         const vector<uint8_t>& publicKey) {
+    if (session_) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Cannot be called in a session"));
+    }
     readerPublicKey_ = publicKey;
     return ndk::ScopedAStatus::ok();
 }
 
 ndk::ScopedAStatus IdentityCredential::createAuthChallenge(int64_t* outChallenge) {
+    if (session_) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Cannot be called in a session"));
+    }
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
+    }
     optional<uint64_t> challenge = hwProxy_->createAuthChallenge();
     if (!challenge) {
         return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
@@ -217,16 +277,22 @@
         const HardwareAuthToken& authToken, const vector<uint8_t>& itemsRequest,
         const vector<uint8_t>& signingKeyBlob, const vector<uint8_t>& sessionTranscript,
         const vector<uint8_t>& readerSignature, const vector<int32_t>& requestCounts) {
-    std::unique_ptr<cppbor::Item> sessionTranscriptItem;
-    if (sessionTranscript.size() > 0) {
-        auto [item, _, message] = cppbor::parse(sessionTranscript);
-        if (item == nullptr) {
-            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
-                    IIdentityCredentialStore::STATUS_INVALID_DATA,
-                    "SessionTranscript contains invalid CBOR"));
-        }
-        sessionTranscriptItem = std::move(item);
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
     }
+
+    // If in a session, ensure the passed-in session transcript matches the
+    // session transcript from the session.
+    if (session_) {
+        if (sessionTranscript != session_->getSessionTranscript()) {
+            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                    IIdentityCredentialStore::STATUS_SESSION_TRANSCRIPT_MISMATCH,
+                    "In a session and passed-in SessionTranscript doesn't match the one "
+                    "from the session"));
+        }
+    }
+
     if (numStartRetrievalCalls_ > 0) {
         if (sessionTranscript_ != sessionTranscript) {
             LOG(ERROR) << "Session Transcript changed";
@@ -390,32 +456,36 @@
         }
     }
 
-    // TODO: move this check to the TA
-#if 1
-    // To prevent replay-attacks, we check that the public part of the ephemeral
-    // key we previously created, is present in the DeviceEngagement part of
-    // SessionTranscript as a COSE_Key, in uncompressed form.
-    //
-    // We do this by just searching for the X and Y coordinates.
-    if (sessionTranscript.size() > 0) {
-        auto [getXYSuccess, ePubX, ePubY] = support::ecPublicKeyGetXandY(ephemeralPublicKey_);
-        if (!getXYSuccess) {
-            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
-                    IIdentityCredentialStore::STATUS_EPHEMERAL_PUBLIC_KEY_NOT_FOUND,
-                    "Error extracting X and Y from ePub"));
-        }
-        if (sessionTranscript.size() > 0 &&
-            !(memmem(sessionTranscript.data(), sessionTranscript.size(), ePubX.data(),
-                     ePubX.size()) != nullptr &&
-              memmem(sessionTranscript.data(), sessionTranscript.size(), ePubY.data(),
-                     ePubY.size()) != nullptr)) {
-            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
-                    IIdentityCredentialStore::STATUS_EPHEMERAL_PUBLIC_KEY_NOT_FOUND,
-                    "Did not find ephemeral public key's X and Y coordinates in "
-                    "SessionTranscript (make sure leading zeroes are not used)"));
+    if (session_) {
+        // If presenting in a session, the TA has already done this check.
+
+    } else {
+        // To prevent replay-attacks, we check that the public part of the ephemeral
+        // key we previously created, is present in the DeviceEngagement part of
+        // SessionTranscript as a COSE_Key, in uncompressed form.
+        //
+        // We do this by just searching for the X and Y coordinates.
+        //
+        // Would be nice to move this check to the TA.
+        if (sessionTranscript.size() > 0) {
+            auto [getXYSuccess, ePubX, ePubY] = support::ecPublicKeyGetXandY(ephemeralPublicKey_);
+            if (!getXYSuccess) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_EPHEMERAL_PUBLIC_KEY_NOT_FOUND,
+                        "Error extracting X and Y from ePub"));
+            }
+            if (sessionTranscript.size() > 0 &&
+                !(memmem(sessionTranscript.data(), sessionTranscript.size(), ePubX.data(),
+                         ePubX.size()) != nullptr &&
+                  memmem(sessionTranscript.data(), sessionTranscript.size(), ePubY.data(),
+                         ePubY.size()) != nullptr)) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_EPHEMERAL_PUBLIC_KEY_NOT_FOUND,
+                        "Did not find ephemeral public key's X and Y coordinates in "
+                        "SessionTranscript (make sure leading zeroes are not used)"));
+            }
         }
     }
-#endif
 
     // itemsRequest: If non-empty, contains request data that may be signed by the
     // reader.  The content can be defined in the way appropriate for the
@@ -537,21 +607,38 @@
 
     // Finally, pass info so the HMAC key can be derived and the TA can start
     // creating the DeviceNameSpaces CBOR...
-    if (sessionTranscript_.size() > 0 && readerPublicKey_.size() > 0 && signingKeyBlob.size() > 0) {
-        // We expect the reader ephemeral public key to be same size and curve
-        // as the ephemeral key we generated (e.g. P-256 key), otherwise ECDH
-        // won't work. So its length should be 65 bytes and it should be
-        // starting with 0x04.
-        if (readerPublicKey_.size() != 65 || readerPublicKey_[0] != 0x04) {
-            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
-                    IIdentityCredentialStore::STATUS_FAILED,
-                    "Reader public key is not in expected format"));
+    if (!session_) {
+        if (sessionTranscript_.size() > 0 && readerPublicKey_.size() > 0 &&
+            signingKeyBlob.size() > 0) {
+            // We expect the reader ephemeral public key to be same size and curve
+            // as the ephemeral key we generated (e.g. P-256 key), otherwise ECDH
+            // won't work. So its length should be 65 bytes and it should be
+            // starting with 0x04.
+            if (readerPublicKey_.size() != 65 || readerPublicKey_[0] != 0x04) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_FAILED,
+                        "Reader public key is not in expected format"));
+            }
+            vector<uint8_t> pubKeyP256(readerPublicKey_.begin() + 1, readerPublicKey_.end());
+            if (!hwProxy_->calcMacKey(sessionTranscript_, pubKeyP256, signingKeyBlob, docType_,
+                                      numNamespacesWithValues, expectedDeviceNameSpacesSize_)) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_FAILED,
+                        "Error starting retrieving entries"));
+            }
         }
-        vector<uint8_t> pubKeyP256(readerPublicKey_.begin() + 1, readerPublicKey_.end());
-        if (!hwProxy_->calcMacKey(sessionTranscript_, pubKeyP256, signingKeyBlob, docType_,
-                                  numNamespacesWithValues, expectedDeviceNameSpacesSize_)) {
-            return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
-                    IIdentityCredentialStore::STATUS_FAILED, "Error starting retrieving entries"));
+    } else {
+        if (session_->getSessionTranscript().size() > 0 &&
+            session_->getReaderEphemeralPublicKey().size() > 0 && signingKeyBlob.size() > 0) {
+            // Don't actually pass the reader ephemeral public key in, the TA will get
+            // it from the session object.
+            //
+            if (!hwProxy_->calcMacKey(sessionTranscript_, {}, signingKeyBlob, docType_,
+                                      numNamespacesWithValues, expectedDeviceNameSpacesSize_)) {
+                return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                        IIdentityCredentialStore::STATUS_FAILED,
+                        "Error starting retrieving entries"));
+            }
         }
     }
 
@@ -665,6 +752,11 @@
 ndk::ScopedAStatus IdentityCredential::startRetrieveEntryValue(
         const string& nameSpace, const string& name, int32_t entrySize,
         const vector<int32_t>& accessControlProfileIds) {
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
+    }
+
     if (name.empty()) {
         return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
                 IIdentityCredentialStore::STATUS_INVALID_DATA, "Name cannot be empty"));
@@ -785,6 +877,11 @@
 
 ndk::ScopedAStatus IdentityCredential::retrieveEntryValue(const vector<uint8_t>& encryptedContent,
                                                           vector<uint8_t>* outContent) {
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
+    }
+
     optional<vector<uint8_t>> content = hwProxy_->retrieveEntryValue(
             encryptedContent, currentNameSpace_, currentName_, currentAccessControlProfileIds_);
     if (!content) {
@@ -829,6 +926,11 @@
 
 ndk::ScopedAStatus IdentityCredential::finishRetrieval(vector<uint8_t>* outMac,
                                                        vector<uint8_t>* outDeviceNameSpaces) {
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
+    }
+
     if (currentNameSpaceDeviceNameSpacesMap_.size() > 0) {
         deviceNameSpacesMap_.add(currentNameSpace_,
                                  std::move(currentNameSpaceDeviceNameSpacesMap_));
@@ -846,18 +948,23 @@
                         .c_str()));
     }
 
-    // If there's no signing key or no sessionTranscript or no reader ephemeral
-    // public key, we return the empty MAC.
+    // If the TA calculated a MAC (it might not have), format it as a COSE_Mac0
+    //
     optional<vector<uint8_t>> mac;
-    if (signingKeyBlob_.size() > 0 && sessionTranscript_.size() > 0 &&
-        readerPublicKey_.size() > 0) {
-        optional<vector<uint8_t>> digestToBeMaced = hwProxy_->finishRetrieval();
-        if (!digestToBeMaced || digestToBeMaced.value().size() != 32) {
+    optional<vector<uint8_t>> digestToBeMaced = hwProxy_->finishRetrieval();
+
+    // The MAC not being set means an error occurred.
+    if (!digestToBeMaced) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_INVALID_DATA, "Error generating digestToBeMaced"));
+    }
+    // Size 0 means that the MAC isn't set. If it's set, it has to be 32 bytes.
+    if (digestToBeMaced.value().size() != 0) {
+        if (digestToBeMaced.value().size() != 32) {
             return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
                     IIdentityCredentialStore::STATUS_INVALID_DATA,
-                    "Error generating digestToBeMaced"));
+                    "Unexpected size for digestToBeMaced"));
         }
-        // Now construct COSE_Mac0 from the returned MAC...
         mac = support::coseMacWithDigest(digestToBeMaced.value(), {} /* data */);
     }
 
@@ -868,6 +975,15 @@
 
 ndk::ScopedAStatus IdentityCredential::generateSigningKeyPair(
         vector<uint8_t>* outSigningKeyBlob, Certificate* outSigningKeyCertificate) {
+    if (session_) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Cannot be called in a session"));
+    }
+    ndk::ScopedAStatus status = ensureHwProxy();
+    if (!status.isOk()) {
+        return status;
+    }
+
     time_t now = time(NULL);
     optional<pair<vector<uint8_t>, vector<uint8_t>>> pair =
             hwProxy_->generateSigningKeyPair(docType_, now);
@@ -885,9 +1001,18 @@
 
 ndk::ScopedAStatus IdentityCredential::updateCredential(
         shared_ptr<IWritableIdentityCredential>* outWritableCredential) {
-    sp<SecureHardwareProvisioningProxy> hwProxy = hwProxyFactory_->createProvisioningProxy();
+    if (session_) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Cannot be called in a session"));
+    }
+    sp<SecureHardwareProvisioningProxy> provisioningHwProxy =
+            hwProxyFactory_->createProvisioningProxy();
+    if (!provisioningHwProxy) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED, "Error creating provisioning proxy"));
+    }
     shared_ptr<WritableIdentityCredential> wc =
-            ndk::SharedRefBase::make<WritableIdentityCredential>(hwProxy, docType_,
+            ndk::SharedRefBase::make<WritableIdentityCredential>(provisioningHwProxy, docType_,
                                                                  testCredential_);
     if (!wc->initializeForUpdate(encryptedCredentialKeys_)) {
         return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
diff --git a/identity/aidl/default/common/IdentityCredential.h b/identity/aidl/default/common/IdentityCredential.h
index ef9d133..2935fb8 100644
--- a/identity/aidl/default/common/IdentityCredential.h
+++ b/identity/aidl/default/common/IdentityCredential.h
@@ -30,6 +30,7 @@
 #include <cppbor.h>
 
 #include "IdentityCredentialStore.h"
+#include "PresentationSession.h"
 #include "SecureHardwareProxy.h"
 
 namespace aidl::android::hardware::identity {
@@ -46,11 +47,11 @@
 class IdentityCredential : public BnIdentityCredential {
   public:
     IdentityCredential(sp<SecureHardwareProxyFactory> hwProxyFactory,
-                       sp<SecureHardwarePresentationProxy> hwProxy,
-                       const vector<uint8_t>& credentialData)
+                       const vector<uint8_t>& credentialData,
+                       std::shared_ptr<PresentationSession> session)
         : hwProxyFactory_(hwProxyFactory),
-          hwProxy_(hwProxy),
           credentialData_(credentialData),
+          session_(std::move(session)),
           numStartRetrievalCalls_(0),
           expectedDeviceNameSpacesSize_(0) {}
 
@@ -94,10 +95,13 @@
                                               bool includeChallenge,
                                               vector<uint8_t>* outProofOfDeletionSignature);
 
+    // Creates and initializes hwProxy_.
+    ndk::ScopedAStatus ensureHwProxy();
+
     // Set by constructor
     sp<SecureHardwareProxyFactory> hwProxyFactory_;
-    sp<SecureHardwarePresentationProxy> hwProxy_;
     vector<uint8_t> credentialData_;
+    shared_ptr<PresentationSession> session_;
     int numStartRetrievalCalls_;
 
     // Set by initialize()
@@ -105,6 +109,9 @@
     bool testCredential_;
     vector<uint8_t> encryptedCredentialKeys_;
 
+    // Set by ensureHwProxy()
+    sp<SecureHardwarePresentationProxy> hwProxy_;
+
     // Set by createEphemeralKeyPair()
     vector<uint8_t> ephemeralPublicKey_;
 
diff --git a/identity/aidl/default/common/IdentityCredentialStore.cpp b/identity/aidl/default/common/IdentityCredentialStore.cpp
index e6b5466..4703ffe 100644
--- a/identity/aidl/default/common/IdentityCredentialStore.cpp
+++ b/identity/aidl/default/common/IdentityCredentialStore.cpp
@@ -20,6 +20,7 @@
 
 #include "IdentityCredential.h"
 #include "IdentityCredentialStore.h"
+#include "PresentationSession.h"
 #include "WritableIdentityCredential.h"
 
 namespace aidl::android::hardware::identity {
@@ -61,9 +62,8 @@
                 "Unsupported cipher suite"));
     }
 
-    sp<SecureHardwarePresentationProxy> hwProxy = hwProxyFactory_->createPresentationProxy();
-    shared_ptr<IdentityCredential> credential =
-            ndk::SharedRefBase::make<IdentityCredential>(hwProxyFactory_, hwProxy, credentialData);
+    shared_ptr<IdentityCredential> credential = ndk::SharedRefBase::make<IdentityCredential>(
+            hwProxyFactory_, credentialData, nullptr /* session */);
     auto ret = credential->initialize();
     if (ret != IIdentityCredentialStore::STATUS_OK) {
         return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
@@ -73,4 +73,25 @@
     return ndk::ScopedAStatus::ok();
 }
 
+ndk::ScopedAStatus IdentityCredentialStore::createPresentationSession(
+        CipherSuite cipherSuite, shared_ptr<IPresentationSession>* outSession) {
+    // We only support CIPHERSUITE_ECDHE_HKDF_ECDSA_WITH_AES_256_GCM_SHA256 right now.
+    if (cipherSuite != CipherSuite::CIPHERSUITE_ECDHE_HKDF_ECDSA_WITH_AES_256_GCM_SHA256) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_CIPHER_SUITE_NOT_SUPPORTED,
+                "Unsupported cipher suite"));
+    }
+
+    sp<SecureHardwareSessionProxy> hwProxy = hwProxyFactory_->createSessionProxy();
+    shared_ptr<PresentationSession> session =
+            ndk::SharedRefBase::make<PresentationSession>(hwProxyFactory_, hwProxy);
+    auto ret = session->initialize();
+    if (ret != IIdentityCredentialStore::STATUS_OK) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                int(ret), "Error initializing PresentationSession"));
+    }
+    *outSession = session;
+    return ndk::ScopedAStatus::ok();
+}
+
 }  // namespace aidl::android::hardware::identity
diff --git a/identity/aidl/default/common/IdentityCredentialStore.h b/identity/aidl/default/common/IdentityCredentialStore.h
index d35e632..77b894d 100644
--- a/identity/aidl/default/common/IdentityCredentialStore.h
+++ b/identity/aidl/default/common/IdentityCredentialStore.h
@@ -47,6 +47,9 @@
     ndk::ScopedAStatus getCredential(CipherSuite cipherSuite, const vector<uint8_t>& credentialData,
                                      shared_ptr<IIdentityCredential>* outCredential) override;
 
+    ndk::ScopedAStatus createPresentationSession(
+            CipherSuite cipherSuite, shared_ptr<IPresentationSession>* outSession) override;
+
   private:
     sp<SecureHardwareProxyFactory> hwProxyFactory_;
 };
diff --git a/identity/aidl/default/common/PresentationSession.cpp b/identity/aidl/default/common/PresentationSession.cpp
new file mode 100644
index 0000000..fbd8972
--- /dev/null
+++ b/identity/aidl/default/common/PresentationSession.cpp
@@ -0,0 +1,149 @@
+/*
+ * Copyright 2021, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "PresentationSession"
+
+#include "PresentationSession.h"
+#include "IdentityCredentialStore.h"
+
+#include <android/hardware/identity/support/IdentityCredentialSupport.h>
+
+#include <string.h>
+
+#include <android-base/logging.h>
+#include <android-base/stringprintf.h>
+
+#include <cppbor.h>
+#include <cppbor_parse.h>
+
+#include "FakeSecureHardwareProxy.h"
+#include "IdentityCredential.h"
+#include "PresentationSession.h"
+
+namespace aidl::android::hardware::identity {
+
+using ::std::optional;
+
+using namespace ::android::hardware::identity;
+
+PresentationSession::~PresentationSession() {}
+
+int PresentationSession::initialize() {
+    if (!hwProxy_->initialize()) {
+        LOG(ERROR) << "hwProxy->initialize failed";
+        return IIdentityCredentialStore::STATUS_FAILED;
+    }
+
+    optional<uint64_t> id = hwProxy_->getId();
+    if (!id) {
+        LOG(ERROR) << "Error getting id for session";
+        return IIdentityCredentialStore::STATUS_FAILED;
+    }
+    id_ = id.value();
+
+    optional<vector<uint8_t>> ephemeralKeyPriv = hwProxy_->getEphemeralKeyPair();
+    if (!ephemeralKeyPriv) {
+        LOG(ERROR) << "Error getting ephemeral private key for session";
+        return IIdentityCredentialStore::STATUS_FAILED;
+    }
+    optional<vector<uint8_t>> ephemeralKeyPair =
+            support::ecPrivateKeyToKeyPair(ephemeralKeyPriv.value());
+    if (!ephemeralKeyPair) {
+        LOG(ERROR) << "Error creating ephemeral key-pair";
+        return IIdentityCredentialStore::STATUS_FAILED;
+    }
+    ephemeralKeyPair_ = ephemeralKeyPair.value();
+
+    optional<uint64_t> authChallenge = hwProxy_->getAuthChallenge();
+    if (!authChallenge) {
+        LOG(ERROR) << "Error getting authChallenge for session";
+        return IIdentityCredentialStore::STATUS_FAILED;
+    }
+    authChallenge_ = authChallenge.value();
+
+    return IIdentityCredentialStore::STATUS_OK;
+}
+
+ndk::ScopedAStatus PresentationSession::getEphemeralKeyPair(vector<uint8_t>* outKeyPair) {
+    *outKeyPair = ephemeralKeyPair_;
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus PresentationSession::getAuthChallenge(int64_t* outChallenge) {
+    *outChallenge = authChallenge_;
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus PresentationSession::setReaderEphemeralPublicKey(
+        const vector<uint8_t>& publicKey) {
+    // We expect the reader ephemeral public key to be same size and curve
+    // as the ephemeral key we generated (e.g. P-256 key), otherwise ECDH
+    // won't work. So its length should be 65 bytes and it should be
+    // starting with 0x04.
+    if (publicKey.size() != 65 || publicKey[0] != 0x04) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED,
+                "Reader public key is not in expected format"));
+    }
+    readerPublicKey_ = publicKey;
+    vector<uint8_t> pubKeyP256(publicKey.begin() + 1, publicKey.end());
+    if (!hwProxy_->setReaderEphemeralPublicKey(pubKeyP256)) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED,
+                "Error setting readerEphemeralPublicKey for session"));
+    }
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus PresentationSession::setSessionTranscript(
+        const vector<uint8_t>& sessionTranscript) {
+    sessionTranscript_ = sessionTranscript;
+    if (!hwProxy_->setSessionTranscript(sessionTranscript)) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                IIdentityCredentialStore::STATUS_FAILED,
+                "Error setting SessionTranscript for session"));
+    }
+    return ndk::ScopedAStatus::ok();
+}
+
+ndk::ScopedAStatus PresentationSession::getCredential(
+        const vector<uint8_t>& credentialData, shared_ptr<IIdentityCredential>* outCredential) {
+    shared_ptr<PresentationSession> p = ref<PresentationSession>();
+    shared_ptr<IdentityCredential> credential =
+            ndk::SharedRefBase::make<IdentityCredential>(hwProxyFactory_, credentialData, p);
+    int ret = credential->initialize();
+    if (ret != IIdentityCredentialStore::STATUS_OK) {
+        return ndk::ScopedAStatus(AStatus_fromServiceSpecificErrorWithMessage(
+                ret, "Error initializing IdentityCredential"));
+    }
+    *outCredential = std::move(credential);
+
+    return ndk::ScopedAStatus::ok();
+}
+
+uint64_t PresentationSession::getSessionId() {
+    return id_;
+}
+
+vector<uint8_t> PresentationSession::getSessionTranscript() {
+    return sessionTranscript_;
+}
+
+vector<uint8_t> PresentationSession::getReaderEphemeralPublicKey() {
+    return readerPublicKey_;
+}
+
+}  // namespace aidl::android::hardware::identity
diff --git a/identity/aidl/default/common/PresentationSession.h b/identity/aidl/default/common/PresentationSession.h
new file mode 100644
index 0000000..76ca67b
--- /dev/null
+++ b/identity/aidl/default/common/PresentationSession.h
@@ -0,0 +1,83 @@
+/*
+ * Copyright 2021, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_HARDWARE_IDENTITY_PRESENTATIONSESSION_H
+#define ANDROID_HARDWARE_IDENTITY_PRESENTATIONSESSION_H
+
+#include <aidl/android/hardware/identity/BnPresentationSession.h>
+#include <android/hardware/identity/support/IdentityCredentialSupport.h>
+
+#include <vector>
+
+#include <cppbor.h>
+
+#include "IdentityCredentialStore.h"
+#include "SecureHardwareProxy.h"
+
+namespace aidl::android::hardware::identity {
+
+using ::aidl::android::hardware::keymaster::HardwareAuthToken;
+using ::aidl::android::hardware::keymaster::VerificationToken;
+using ::android::sp;
+using ::android::hardware::identity::SecureHardwareSessionProxy;
+using ::std::vector;
+
+class PresentationSession : public BnPresentationSession {
+  public:
+    PresentationSession(sp<SecureHardwareProxyFactory> hwProxyFactory,
+                        sp<SecureHardwareSessionProxy> hwProxy)
+        : hwProxyFactory_(std::move(hwProxyFactory)), hwProxy_(std::move(hwProxy)) {}
+
+    virtual ~PresentationSession();
+
+    // Creates ephemeral key and auth-challenge in TA. Returns a status code from
+    // IIdentityCredentialStore. Must be called right after construction.
+    int initialize();
+
+    uint64_t getSessionId();
+
+    vector<uint8_t> getSessionTranscript();
+    vector<uint8_t> getReaderEphemeralPublicKey();
+
+    // Methods from IPresentationSession follow.
+    ndk::ScopedAStatus getEphemeralKeyPair(vector<uint8_t>* outKeyPair) override;
+    ndk::ScopedAStatus getAuthChallenge(int64_t* outChallenge) override;
+    ndk::ScopedAStatus setReaderEphemeralPublicKey(const vector<uint8_t>& publicKey) override;
+    ndk::ScopedAStatus setSessionTranscript(const vector<uint8_t>& sessionTranscript) override;
+
+    ndk::ScopedAStatus getCredential(const vector<uint8_t>& credentialData,
+                                     shared_ptr<IIdentityCredential>* outCredential) override;
+
+  private:
+    // Set by constructor
+    sp<SecureHardwareProxyFactory> hwProxyFactory_;
+    sp<SecureHardwareSessionProxy> hwProxy_;
+
+    // Set by initialize()
+    uint64_t id_;
+    vector<uint8_t> ephemeralKeyPair_;
+    uint64_t authChallenge_;
+
+    // Set by setReaderEphemeralPublicKey()
+    vector<uint8_t> readerPublicKey_;
+
+    // Set by setSessionTranscript()
+    vector<uint8_t> sessionTranscript_;
+};
+
+}  // namespace aidl::android::hardware::identity
+
+#endif  // ANDROID_HARDWARE_IDENTITY_PRESENTATIONSESSION_H
diff --git a/identity/aidl/default/common/SecureHardwareProxy.h b/identity/aidl/default/common/SecureHardwareProxy.h
index a1ed1ef..a580444 100644
--- a/identity/aidl/default/common/SecureHardwareProxy.h
+++ b/identity/aidl/default/common/SecureHardwareProxy.h
@@ -42,6 +42,7 @@
 // Forward declare.
 //
 class SecureHardwareProvisioningProxy;
+class SecureHardwareSessionProxy;
 class SecureHardwarePresentationProxy;
 
 // This is a class used to create proxies.
@@ -52,6 +53,7 @@
     virtual ~SecureHardwareProxyFactory() {}
 
     virtual sp<SecureHardwareProvisioningProxy> createProvisioningProxy() = 0;
+    virtual sp<SecureHardwareSessionProxy> createSessionProxy() = 0;
     virtual sp<SecureHardwarePresentationProxy> createPresentationProxy() = 0;
 };
 
@@ -64,8 +66,12 @@
 
     virtual bool initialize(bool testCredential) = 0;
 
-    virtual bool initializeForUpdate(bool testCredential, string docType,
-                                     vector<uint8_t> encryptedCredentialKeys) = 0;
+    virtual bool initializeForUpdate(bool testCredential, const string& docType,
+                                     const vector<uint8_t>& encryptedCredentialKeys) = 0;
+
+    virtual optional<uint32_t> getId() = 0;
+
+    virtual bool shutdown() = 0;
 
     // Returns public key certificate chain with attestation.
     //
@@ -76,7 +82,7 @@
     virtual optional<vector<uint8_t>> createCredentialKey(const vector<uint8_t>& challenge,
                                                           const vector<uint8_t>& applicationId) = 0;
 
-    virtual bool startPersonalization(int accessControlProfileCount, vector<int> entryCounts,
+    virtual bool startPersonalization(int accessControlProfileCount, const vector<int>& entryCounts,
                                       const string& docType,
                                       size_t expectedProofOfProvisioningSize) = 0;
 
@@ -98,8 +104,6 @@
 
     // Returns encryptedCredentialKeys (80 bytes).
     virtual optional<vector<uint8_t>> finishGetCredentialData(const string& docType) = 0;
-
-    virtual bool shutdown() = 0;
 };
 
 enum AccessCheckResult {
@@ -110,6 +114,30 @@
     kReaderAuthenticationFailed,
 };
 
+// The proxy used for sessions.
+//
+class SecureHardwareSessionProxy : public RefBase {
+  public:
+    SecureHardwareSessionProxy() {}
+
+    virtual ~SecureHardwareSessionProxy() {}
+
+    virtual bool initialize() = 0;
+
+    virtual optional<uint32_t> getId() = 0;
+
+    virtual bool shutdown() = 0;
+
+    virtual optional<uint64_t> getAuthChallenge() = 0;
+
+    // Returns private key
+    virtual optional<vector<uint8_t>> getEphemeralKeyPair() = 0;
+
+    virtual bool setReaderEphemeralPublicKey(const vector<uint8_t>& readerEphemeralPublicKey) = 0;
+
+    virtual bool setSessionTranscript(const vector<uint8_t>& sessionTranscript) = 0;
+};
+
 // The proxy used for presentation.
 //
 class SecureHardwarePresentationProxy : public RefBase {
@@ -117,12 +145,16 @@
     SecureHardwarePresentationProxy() {}
     virtual ~SecureHardwarePresentationProxy() {}
 
-    virtual bool initialize(bool testCredential, string docType,
-                            vector<uint8_t> encryptedCredentialKeys) = 0;
+    virtual bool initialize(uint32_t sessionId, bool testCredential, const string& docType,
+                            const vector<uint8_t>& encryptedCredentialKeys) = 0;
+
+    virtual optional<uint32_t> getId() = 0;
+
+    virtual bool shutdown() = 0;
 
     // Returns publicKeyCert (1st component) and signingKeyBlob (2nd component)
-    virtual optional<pair<vector<uint8_t>, vector<uint8_t>>> generateSigningKeyPair(string docType,
-                                                                                    time_t now) = 0;
+    virtual optional<pair<vector<uint8_t>, vector<uint8_t>>> generateSigningKeyPair(
+            const string& docType, time_t now) = 0;
 
     // Returns private key
     virtual optional<vector<uint8_t>> createEphemeralKeyPair() = 0;
@@ -174,8 +206,6 @@
     virtual optional<vector<uint8_t>> proveOwnership(const string& docType, bool testCredential,
                                                      const vector<uint8_t>& challenge,
                                                      size_t proofOfOwnershipCborSize) = 0;
-
-    virtual bool shutdown() = 0;
 };
 
 }  // namespace android::hardware::identity
diff --git a/identity/aidl/default/identity-default.xml b/identity/aidl/default/identity-default.xml
index a074250..cc0ddc7 100644
--- a/identity/aidl/default/identity-default.xml
+++ b/identity/aidl/default/identity-default.xml
@@ -1,7 +1,7 @@
 <manifest version="1.0" type="device">
     <hal format="aidl">
         <name>android.hardware.identity</name>
-        <version>3</version>
+        <version>4</version>
         <interface>
             <name>IIdentityCredentialStore</name>
             <instance>default</instance>
diff --git a/identity/aidl/default/libeic/EicCommon.h b/identity/aidl/default/libeic/EicCommon.h
index 476276e..2a08a35 100644
--- a/identity/aidl/default/libeic/EicCommon.h
+++ b/identity/aidl/default/libeic/EicCommon.h
@@ -21,6 +21,9 @@
 #ifndef ANDROID_HARDWARE_IDENTITY_EIC_COMMON_H
 #define ANDROID_HARDWARE_IDENTITY_EIC_COMMON_H
 
+// KeyMint auth-challenges are 64-bit numbers and 0 typically means unset.
+#define EIC_KM_AUTH_CHALLENGE_UNSET 0
+
 // Feature version 202009:
 //
 //         CredentialKeys = [
diff --git a/identity/aidl/default/libeic/EicOps.h b/identity/aidl/default/libeic/EicOps.h
index d4fcf0e..aa26e62 100644
--- a/identity/aidl/default/libeic/EicOps.h
+++ b/identity/aidl/default/libeic/EicOps.h
@@ -141,6 +141,10 @@
 // String length, see strlen(3).
 size_t eicStrLen(const char* s);
 
+// Locate a substring, see memmem(3)
+void* eicMemMem(const uint8_t* haystack, size_t haystackLen, const uint8_t* needle,
+                size_t needleLen);
+
 // Memory compare, see CRYPTO_memcmp(3SSL)
 //
 // It takes an amount of time dependent on len, but independent of the contents of the
@@ -151,6 +155,12 @@
 // Random number generation.
 bool eicOpsRandom(uint8_t* buf, size_t numBytes);
 
+// Creates a new non-zero identifier in |id|.
+//
+// Is guaranteed to be non-zero and different than what is already in |id|.
+//
+bool eicNextId(uint32_t* id);
+
 // If |testCredential| is true, returns the 128-bit AES Hardware-Bound Key (16 bytes).
 //
 // Otherwise returns all zeroes (16 bytes).
@@ -295,6 +305,8 @@
                              int verificationTokenSecurityLevel,
                              const uint8_t* verificationTokenMac, size_t verificationTokenMacSize);
 
+// Also see eicOpsLookupActiveSessionFromId() defined in EicSession.h
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/identity/aidl/default/libeic/EicPresentation.c b/identity/aidl/default/libeic/EicPresentation.c
index 0d03ae9..104a559 100644
--- a/identity/aidl/default/libeic/EicPresentation.c
+++ b/identity/aidl/default/libeic/EicPresentation.c
@@ -16,11 +16,17 @@
 
 #include "EicPresentation.h"
 #include "EicCommon.h"
+#include "EicSession.h"
 
 #include <inttypes.h>
 
-bool eicPresentationInit(EicPresentation* ctx, bool testCredential, const char* docType,
-                         size_t docTypeLength, const uint8_t* encryptedCredentialKeys,
+// Global used for assigning ids for presentation objects.
+//
+static uint32_t gPresentationLastIdAssigned = 0;
+
+bool eicPresentationInit(EicPresentation* ctx, uint32_t sessionId, bool testCredential,
+                         const char* docType, size_t docTypeLength,
+                         const uint8_t* encryptedCredentialKeys,
                          size_t encryptedCredentialKeysSize) {
     uint8_t credentialKeys[EIC_CREDENTIAL_KEYS_CBOR_SIZE_FEATURE_VERSION_202101];
     bool expectPopSha256 = false;
@@ -39,6 +45,13 @@
     }
 
     eicMemSet(ctx, '\0', sizeof(EicPresentation));
+    ctx->sessionId = sessionId;
+
+    if (!eicNextId(&gPresentationLastIdAssigned)) {
+        eicDebug("Error getting id for object");
+        return false;
+    }
+    ctx->id = gPresentationLastIdAssigned;
 
     if (!eicOpsDecryptAes128Gcm(eicOpsGetHardwareBoundKey(testCredential), encryptedCredentialKeys,
                                 encryptedCredentialKeysSize,
@@ -86,6 +99,23 @@
     if (expectPopSha256) {
         eicMemCpy(ctx->proofOfProvisioningSha256, credentialKeys + 54, EIC_SHA256_DIGEST_SIZE);
     }
+
+    eicDebug("Initialized presentation with id %" PRIu32, ctx->id);
+    return true;
+}
+
+bool eicPresentationShutdown(EicPresentation* ctx) {
+    if (ctx->id == 0) {
+        eicDebug("Trying to shut down presentation with id 0");
+        return false;
+    }
+    eicDebug("Shut down presentation with id %" PRIu32, ctx->id);
+    eicMemSet(ctx, '\0', sizeof(EicPresentation));
+    return true;
+}
+
+bool eicPresentationGetId(EicPresentation* ctx, uint32_t* outId) {
+    *outId = ctx->id;
     return true;
 }
 
@@ -174,7 +204,7 @@
             eicDebug("Failed generating random challenge");
             return false;
         }
-    } while (ctx->authChallenge == 0);
+    } while (ctx->authChallenge == EIC_KM_AUTH_CHALLENGE_UNSET);
     eicDebug("Created auth challenge %" PRIu64, ctx->authChallenge);
     *authChallenge = ctx->authChallenge;
     return true;
@@ -190,6 +220,24 @@
                                            int coseSignAlg,
                                            const uint8_t* readerSignatureOfToBeSigned,
                                            size_t readerSignatureOfToBeSignedSize) {
+    if (ctx->sessionId != 0) {
+        EicSession* session = eicSessionGetForId(ctx->sessionId);
+        if (session == NULL) {
+            eicDebug("Error looking up session for sessionId %" PRIu32, ctx->sessionId);
+            return false;
+        }
+        EicSha256Ctx sha256;
+        uint8_t sessionTranscriptSha256[EIC_SHA256_DIGEST_SIZE];
+        eicOpsSha256Init(&sha256);
+        eicOpsSha256Update(&sha256, sessionTranscript, sessionTranscriptSize);
+        eicOpsSha256Final(&sha256, sessionTranscriptSha256);
+        if (eicCryptoMemCmp(sessionTranscriptSha256, session->sessionTranscriptSha256,
+                            EIC_SHA256_DIGEST_SIZE) != 0) {
+            eicDebug("SessionTranscript mismatch");
+            return false;
+        }
+    }
+
     if (ctx->readerPublicKeySize == 0) {
         eicDebug("No public key for reader");
         return false;
@@ -330,6 +378,20 @@
     return true;
 }
 
+static bool getChallenge(EicPresentation* ctx, uint64_t* outAuthChallenge) {
+    // Use authChallenge from session if applicable.
+    *outAuthChallenge = ctx->authChallenge;
+    if (ctx->sessionId != 0) {
+        EicSession* session = eicSessionGetForId(ctx->sessionId);
+        if (session == NULL) {
+            eicDebug("Error looking up session for sessionId %" PRIu32, ctx->sessionId);
+            return false;
+        }
+        *outAuthChallenge = session->authChallenge;
+    }
+    return true;
+}
+
 bool eicPresentationSetAuthToken(EicPresentation* ctx, uint64_t challenge, uint64_t secureUserId,
                                  uint64_t authenticatorId, int hardwareAuthenticatorType,
                                  uint64_t timeStamp, const uint8_t* mac, size_t macSize,
@@ -338,14 +400,19 @@
                                  int verificationTokenSecurityLevel,
                                  const uint8_t* verificationTokenMac,
                                  size_t verificationTokenMacSize) {
+    uint64_t authChallenge;
+    if (!getChallenge(ctx, &authChallenge)) {
+        return false;
+    }
+
     // It doesn't make sense to accept any tokens if eicPresentationCreateAuthChallenge()
     // was never called.
-    if (ctx->authChallenge == 0) {
-        eicDebug("Trying validate tokens when no auth-challenge was previously generated");
+    if (authChallenge == EIC_KM_AUTH_CHALLENGE_UNSET) {
+        eicDebug("Trying to validate tokens when no auth-challenge was previously generated");
         return false;
     }
     // At least the verification-token must have the same challenge as what was generated.
-    if (verificationTokenChallenge != ctx->authChallenge) {
+    if (verificationTokenChallenge != authChallenge) {
         eicDebug("Challenge in verification token does not match the challenge "
                  "previously generated");
         return false;
@@ -354,6 +421,7 @@
                 challenge, secureUserId, authenticatorId, hardwareAuthenticatorType, timeStamp, mac,
                 macSize, verificationTokenChallenge, verificationTokenTimestamp,
                 verificationTokenSecurityLevel, verificationTokenMac, verificationTokenMacSize)) {
+        eicDebug("Error validating authToken");
         return false;
     }
     ctx->authTokenChallenge = challenge;
@@ -377,11 +445,16 @@
     // Only ACP with auth-on-every-presentation - those with timeout == 0 - need the
     // challenge to match...
     if (timeoutMillis == 0) {
-        if (ctx->authTokenChallenge != ctx->authChallenge) {
+        uint64_t authChallenge;
+        if (!getChallenge(ctx, &authChallenge)) {
+            return false;
+        }
+
+        if (ctx->authTokenChallenge != authChallenge) {
             eicDebug("Challenge in authToken (%" PRIu64
                      ") doesn't match the challenge "
                      "that was created (%" PRIu64 ") for this session",
-                     ctx->authTokenChallenge, ctx->authChallenge);
+                     ctx->authTokenChallenge, authChallenge);
             return false;
         }
     }
@@ -490,6 +563,25 @@
                                const uint8_t signingKeyBlob[60], const char* docType,
                                size_t docTypeLength, unsigned int numNamespacesWithValues,
                                size_t expectedDeviceNamespacesSize) {
+    if (ctx->sessionId != 0) {
+        EicSession* session = eicSessionGetForId(ctx->sessionId);
+        if (session == NULL) {
+            eicDebug("Error looking up session for sessionId %" PRIu32, ctx->sessionId);
+            return false;
+        }
+        EicSha256Ctx sha256;
+        uint8_t sessionTranscriptSha256[EIC_SHA256_DIGEST_SIZE];
+        eicOpsSha256Init(&sha256);
+        eicOpsSha256Update(&sha256, sessionTranscript, sessionTranscriptSize);
+        eicOpsSha256Final(&sha256, sessionTranscriptSha256);
+        if (eicCryptoMemCmp(sessionTranscriptSha256, session->sessionTranscriptSha256,
+                            EIC_SHA256_DIGEST_SIZE) != 0) {
+            eicDebug("SessionTranscript mismatch");
+            return false;
+        }
+        readerEphemeralPublicKey = session->readerEphemeralPublicKey;
+    }
+
     uint8_t signingKeyPriv[EIC_P256_PRIV_KEY_SIZE];
     if (!eicOpsDecryptAes128Gcm(ctx->storageKey, signingKeyBlob, 60, (const uint8_t*)docType,
                                 docTypeLength, signingKeyPriv)) {
diff --git a/identity/aidl/default/libeic/EicPresentation.h b/identity/aidl/default/libeic/EicPresentation.h
index 6f7f432..a031890 100644
--- a/identity/aidl/default/libeic/EicPresentation.h
+++ b/identity/aidl/default/libeic/EicPresentation.h
@@ -30,7 +30,13 @@
 // The maximum size we support for public keys in reader certificates.
 #define EIC_PRESENTATION_MAX_READER_PUBLIC_KEY_SIZE 65
 
+// Constant used to convey that no session is associated with a presentation.
+#define EIC_PRESENTATION_ID_UNSET 0
+
 typedef struct {
+    // A non-zero number unique for this EicPresentation instance
+    uint32_t id;
+
     int featureLevel;
 
     uint8_t storageKey[EIC_AES_128_KEY_SIZE];
@@ -38,6 +44,10 @@
 
     uint8_t ephemeralPrivateKey[EIC_P256_PRIV_KEY_SIZE];
 
+    // If non-zero (not EIC_PRESENTATION_ID_UNSET), the id of the EicSession object this
+    // presentation object is associated with.
+    uint32_t sessionId;
+
     // The challenge generated with eicPresentationCreateAuthChallenge()
     uint64_t authChallenge;
 
@@ -93,10 +103,18 @@
     EicCbor cbor;
 } EicPresentation;
 
-bool eicPresentationInit(EicPresentation* ctx, bool testCredential, const char* docType,
-                         size_t docTypeLength, const uint8_t* encryptedCredentialKeys,
+// If sessionId is zero (EIC_PRESENTATION_ID_UNSET), the presentation object is not associated
+// with a session object. Otherwise it's the id of the session object.
+//
+bool eicPresentationInit(EicPresentation* ctx, uint32_t sessionId, bool testCredential,
+                         const char* docType, size_t docTypeLength,
+                         const uint8_t* encryptedCredentialKeys,
                          size_t encryptedCredentialKeysSize);
 
+bool eicPresentationShutdown(EicPresentation* ctx);
+
+bool eicPresentationGetId(EicPresentation* ctx, uint32_t* outId);
+
 bool eicPresentationGenerateSigningKeyPair(EicPresentation* ctx, const char* docType,
                                            size_t docTypeLength, time_t now,
                                            uint8_t* publicKeyCert, size_t* publicKeyCertSize,
diff --git a/identity/aidl/default/libeic/EicProvisioning.c b/identity/aidl/default/libeic/EicProvisioning.c
index c9df4fd..a241b71 100644
--- a/identity/aidl/default/libeic/EicProvisioning.c
+++ b/identity/aidl/default/libeic/EicProvisioning.c
@@ -17,8 +17,21 @@
 #include "EicProvisioning.h"
 #include "EicCommon.h"
 
+#include <inttypes.h>
+
+// Global used for assigning ids for provisioning objects.
+//
+static uint32_t gProvisioningLastIdAssigned = 0;
+
 bool eicProvisioningInit(EicProvisioning* ctx, bool testCredential) {
     eicMemSet(ctx, '\0', sizeof(EicProvisioning));
+
+    if (!eicNextId(&gProvisioningLastIdAssigned)) {
+        eicDebug("Error getting id for object");
+        return false;
+    }
+    ctx->id = gProvisioningLastIdAssigned;
+
     ctx->testCredential = testCredential;
     if (!eicOpsRandom(ctx->storageKey, EIC_AES_128_KEY_SIZE)) {
         return false;
@@ -47,6 +60,13 @@
     }
 
     eicMemSet(ctx, '\0', sizeof(EicProvisioning));
+
+    if (!eicNextId(&gProvisioningLastIdAssigned)) {
+        eicDebug("Error getting id for object");
+        return false;
+    }
+    ctx->id = gProvisioningLastIdAssigned;
+
     ctx->testCredential = testCredential;
 
     if (!eicOpsDecryptAes128Gcm(eicOpsGetHardwareBoundKey(testCredential), encryptedCredentialKeys,
@@ -96,6 +116,21 @@
     return true;
 }
 
+bool eicProvisioningShutdown(EicProvisioning* ctx) {
+    if (ctx->id == 0) {
+        eicDebug("Trying to shut down provsioning with id 0");
+        return false;
+    }
+    eicDebug("Shut down provsioning with id %" PRIu32, ctx->id);
+    eicMemSet(ctx, '\0', sizeof(EicProvisioning));
+    return true;
+}
+
+bool eicProvisioningGetId(EicProvisioning* ctx, uint32_t* outId) {
+    *outId = ctx->id;
+    return true;
+}
+
 bool eicProvisioningCreateCredentialKey(EicProvisioning* ctx, const uint8_t* challenge,
                                         size_t challengeSize, const uint8_t* applicationId,
                                         size_t applicationIdSize, uint8_t* publicKeyCert,
diff --git a/identity/aidl/default/libeic/EicProvisioning.h b/identity/aidl/default/libeic/EicProvisioning.h
index 92f1e4a..d94f8f1 100644
--- a/identity/aidl/default/libeic/EicProvisioning.h
+++ b/identity/aidl/default/libeic/EicProvisioning.h
@@ -31,6 +31,9 @@
 #define EIC_MAX_NUM_ACCESS_CONTROL_PROFILE_IDS 32
 
 typedef struct {
+    // A non-zero number unique for this EicProvisioning instance
+    uint32_t id;
+
     // Set by eicCreateCredentialKey() OR eicProvisioningInitForUpdate()
     uint8_t credentialPrivateKey[EIC_P256_PRIV_KEY_SIZE];
 
@@ -68,6 +71,10 @@
                                   size_t docTypeLength, const uint8_t* encryptedCredentialKeys,
                                   size_t encryptedCredentialKeysSize);
 
+bool eicProvisioningShutdown(EicProvisioning* ctx);
+
+bool eicProvisioningGetId(EicProvisioning* ctx, uint32_t* outId);
+
 bool eicProvisioningCreateCredentialKey(EicProvisioning* ctx, const uint8_t* challenge,
                                         size_t challengeSize, const uint8_t* applicationId,
                                         size_t applicationIdSize, uint8_t* publicKeyCert,
diff --git a/identity/aidl/default/libeic/EicSession.c b/identity/aidl/default/libeic/EicSession.c
new file mode 100644
index 0000000..d0c7a0d
--- /dev/null
+++ b/identity/aidl/default/libeic/EicSession.c
@@ -0,0 +1,120 @@
+/*
+ * Copyright 2020, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <inttypes.h>
+
+#include "EicCommon.h"
+#include "EicSession.h"
+
+// Global used for assigning ids for session objects.
+//
+static uint32_t gSessionLastIdAssigned = 0;
+
+// The current session object or NULL if never initialized or if it has been shut down.
+//
+static EicSession* gSessionCurrent = NULL;
+
+EicSession* eicSessionGetForId(uint32_t sessionId) {
+    if (gSessionCurrent != NULL && gSessionCurrent->id == sessionId) {
+        return gSessionCurrent;
+    }
+    return NULL;
+}
+
+bool eicSessionInit(EicSession* ctx) {
+    eicMemSet(ctx, '\0', sizeof(EicSession));
+
+    if (!eicNextId(&gSessionLastIdAssigned)) {
+        eicDebug("Error getting id for object");
+        return false;
+    }
+    ctx->id = gSessionLastIdAssigned;
+
+    do {
+        if (!eicOpsRandom((uint8_t*)&(ctx->authChallenge), sizeof(ctx->authChallenge))) {
+            eicDebug("Failed generating random challenge");
+            return false;
+        }
+    } while (ctx->authChallenge == EIC_KM_AUTH_CHALLENGE_UNSET);
+
+    if (!eicOpsCreateEcKey(ctx->ephemeralPrivateKey, ctx->ephemeralPublicKey)) {
+        eicDebug("Error creating ephemeral key-pair");
+        return false;
+    }
+
+    gSessionCurrent = ctx;
+    eicDebug("Initialized session with id %" PRIu32, ctx->id);
+    return true;
+}
+
+bool eicSessionShutdown(EicSession* ctx) {
+    if (ctx->id == 0) {
+        eicDebug("Trying to shut down session with id 0");
+        return false;
+    }
+    eicDebug("Shut down session with id %" PRIu32, ctx->id);
+    eicMemSet(ctx, '\0', sizeof(EicSession));
+    gSessionCurrent = NULL;
+    return true;
+}
+
+bool eicSessionGetId(EicSession* ctx, uint32_t* outId) {
+    *outId = ctx->id;
+    return true;
+}
+
+bool eicSessionGetAuthChallenge(EicSession* ctx, uint64_t* outAuthChallenge) {
+    *outAuthChallenge = ctx->authChallenge;
+    return true;
+}
+
+bool eicSessionGetEphemeralKeyPair(EicSession* ctx,
+                                   uint8_t ephemeralPrivateKey[EIC_P256_PRIV_KEY_SIZE]) {
+    eicMemCpy(ephemeralPrivateKey, ctx->ephemeralPrivateKey, EIC_P256_PRIV_KEY_SIZE);
+    return true;
+}
+
+bool eicSessionSetReaderEphemeralPublicKey(
+        EicSession* ctx, const uint8_t readerEphemeralPublicKey[EIC_P256_PUB_KEY_SIZE]) {
+    eicMemCpy(ctx->readerEphemeralPublicKey, readerEphemeralPublicKey, EIC_P256_PUB_KEY_SIZE);
+    return true;
+}
+
+bool eicSessionSetSessionTranscript(EicSession* ctx, const uint8_t* sessionTranscript,
+                                    size_t sessionTranscriptSize) {
+    // Only accept the SessionTranscript if X and Y from the ephemeral key
+    // we created is somewhere in SessionTranscript...
+    //
+    if (eicMemMem(sessionTranscript, sessionTranscriptSize, ctx->ephemeralPublicKey,
+                  EIC_P256_PUB_KEY_SIZE / 2) == NULL) {
+        eicDebug("Error finding X from ephemeralPublicKey in sessionTranscript");
+        return false;
+    }
+    if (eicMemMem(sessionTranscript, sessionTranscriptSize,
+                  ctx->ephemeralPublicKey + EIC_P256_PUB_KEY_SIZE / 2,
+                  EIC_P256_PUB_KEY_SIZE / 2) == NULL) {
+        eicDebug("Error finding Y from ephemeralPublicKey in sessionTranscript");
+        return false;
+    }
+
+    // To save space we only store the SHA-256 of SessionTranscript
+    //
+    EicSha256Ctx shaCtx;
+    eicOpsSha256Init(&shaCtx);
+    eicOpsSha256Update(&shaCtx, sessionTranscript, sessionTranscriptSize);
+    eicOpsSha256Final(&shaCtx, ctx->sessionTranscriptSha256);
+    return true;
+}
diff --git a/identity/aidl/default/libeic/EicSession.h b/identity/aidl/default/libeic/EicSession.h
new file mode 100644
index 0000000..0303dae
--- /dev/null
+++ b/identity/aidl/default/libeic/EicSession.h
@@ -0,0 +1,73 @@
+/*
+ * Copyright 2021, The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if !defined(EIC_INSIDE_LIBEIC_H) && !defined(EIC_COMPILATION)
+#error "Never include this file directly, include libeic.h instead."
+#endif
+
+#ifndef ANDROID_HARDWARE_IDENTITY_EIC_SESSION_H
+#define ANDROID_HARDWARE_IDENTITY_EIC_SESSION_H
+
+#include "EicOps.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct {
+    // A non-zero number unique for this EicSession instance
+    uint32_t id;
+
+    // The challenge generated at construction time by eicSessionInit().
+    uint64_t authChallenge;
+
+    uint8_t ephemeralPrivateKey[EIC_P256_PRIV_KEY_SIZE];
+    uint8_t ephemeralPublicKey[EIC_P256_PUB_KEY_SIZE];
+
+    uint8_t readerEphemeralPublicKey[EIC_P256_PUB_KEY_SIZE];
+
+    uint8_t sessionTranscriptSha256[EIC_SHA256_DIGEST_SIZE];
+
+} EicSession;
+
+bool eicSessionInit(EicSession* ctx);
+
+bool eicSessionShutdown(EicSession* ctx);
+
+bool eicSessionGetId(EicSession* ctx, uint32_t* outId);
+
+bool eicSessionGetAuthChallenge(EicSession* ctx, uint64_t* outAuthChallenge);
+
+bool eicSessionGetEphemeralKeyPair(EicSession* ctx,
+                                   uint8_t ephemeralPrivateKey[EIC_P256_PRIV_KEY_SIZE]);
+
+bool eicSessionSetReaderEphemeralPublicKey(
+        EicSession* ctx, const uint8_t readerEphemeralPublicKey[EIC_P256_PUB_KEY_SIZE]);
+
+bool eicSessionSetSessionTranscript(EicSession* ctx, const uint8_t* sessionTranscript,
+                                    size_t sessionTranscriptSize);
+
+// Looks up an active session with the given id.
+//
+// Returns NULL if no active session with the given id is found.
+//
+EicSession* eicSessionGetForId(uint32_t sessionId);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // ANDROID_HARDWARE_IDENTITY_EIC_PRESENTATION_H
diff --git a/identity/aidl/default/libeic/libeic.h b/identity/aidl/default/libeic/libeic.h
index 20c8896..d89fc9a 100644
--- a/identity/aidl/default/libeic/libeic.h
+++ b/identity/aidl/default/libeic/libeic.h
@@ -27,10 +27,11 @@
  */
 #define EIC_INSIDE_LIBEIC_H
 #include "EicCbor.h"
+#include "EicCommon.h"
 #include "EicOps.h"
 #include "EicPresentation.h"
 #include "EicProvisioning.h"
-#include "EicCommon.h"
+#include "EicSession.h"
 #undef EIC_INSIDE_LIBEIC_H
 
 #ifdef __cplusplus
diff --git a/identity/aidl/vts/Android.bp b/identity/aidl/vts/Android.bp
index e5de91e..7b6f2c8 100644
--- a/identity/aidl/vts/Android.bp
+++ b/identity/aidl/vts/Android.bp
@@ -28,6 +28,7 @@
         "EndToEndTests.cpp",
         "TestCredentialTests.cpp",
         "AuthenticationKeyTests.cpp",
+        "PresentationSessionTests.cpp",
     ],
     shared_libs: [
         "libbinder",
@@ -40,9 +41,9 @@
         "libpuresoftkeymasterdevice",
         "android.hardware.keymaster@4.0",
         "android.hardware.identity-support-lib",
-        "android.hardware.identity-V3-cpp",
-        "android.hardware.keymaster-V3-cpp",
-        "android.hardware.keymaster-V3-ndk",
+        "android.hardware.identity-V4-cpp",
+        "android.hardware.keymaster-V4-cpp",
+        "android.hardware.keymaster-V4-ndk",
         "libkeymaster4support",
         "libkeymaster4_1support",
     ],
diff --git a/identity/aidl/vts/PresentationSessionTests.cpp b/identity/aidl/vts/PresentationSessionTests.cpp
new file mode 100644
index 0000000..88acb26
--- /dev/null
+++ b/identity/aidl/vts/PresentationSessionTests.cpp
@@ -0,0 +1,197 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "PresentationSessionTests"
+
+#include <aidl/Gtest.h>
+#include <aidl/Vintf.h>
+#include <aidl/android/hardware/keymaster/HardwareAuthToken.h>
+#include <aidl/android/hardware/keymaster/VerificationToken.h>
+#include <android-base/logging.h>
+#include <android/hardware/identity/IIdentityCredentialStore.h>
+#include <android/hardware/identity/support/IdentityCredentialSupport.h>
+#include <binder/IServiceManager.h>
+#include <binder/ProcessState.h>
+#include <cppbor.h>
+#include <cppbor_parse.h>
+#include <gtest/gtest.h>
+#include <future>
+#include <map>
+#include <utility>
+
+#include "Util.h"
+
+namespace android::hardware::identity {
+
+using std::endl;
+using std::make_pair;
+using std::map;
+using std::optional;
+using std::pair;
+using std::string;
+using std::tie;
+using std::vector;
+
+using ::android::sp;
+using ::android::String16;
+using ::android::binder::Status;
+
+using ::android::hardware::keymaster::HardwareAuthToken;
+using ::android::hardware::keymaster::VerificationToken;
+
+class PresentationSessionTests : public testing::TestWithParam<string> {
+  public:
+    virtual void SetUp() override {
+        credentialStore_ = android::waitForDeclaredService<IIdentityCredentialStore>(
+                String16(GetParam().c_str()));
+        ASSERT_NE(credentialStore_, nullptr);
+        halApiVersion_ = credentialStore_->getInterfaceVersion();
+    }
+
+    void provisionData();
+
+    void provisionSingleDocument(const string& docType, vector<uint8_t>* outCredentialData,
+                                 vector<uint8_t>* outCredentialPubKey);
+
+    // Set by provisionData
+    vector<uint8_t> credential1Data_;
+    vector<uint8_t> credential1PubKey_;
+    vector<uint8_t> credential2Data_;
+    vector<uint8_t> credential2PubKey_;
+
+    sp<IIdentityCredentialStore> credentialStore_;
+    int halApiVersion_;
+};
+
+void PresentationSessionTests::provisionData() {
+    provisionSingleDocument("org.iso.18013-5.2019.mdl", &credential1Data_, &credential1PubKey_);
+    provisionSingleDocument("org.blah.OtherhDocTypeXX", &credential2Data_, &credential2PubKey_);
+}
+
+void PresentationSessionTests::provisionSingleDocument(const string& docType,
+                                                       vector<uint8_t>* outCredentialData,
+                                                       vector<uint8_t>* outCredentialPubKey) {
+    bool testCredential = true;
+    sp<IWritableIdentityCredential> wc;
+    ASSERT_TRUE(credentialStore_->createCredential(docType, testCredential, &wc).isOk());
+
+    vector<uint8_t> attestationApplicationId;
+    vector<uint8_t> attestationChallenge = {1};
+    vector<Certificate> certChain;
+    ASSERT_TRUE(wc->getAttestationCertificate(attestationApplicationId, attestationChallenge,
+                                              &certChain)
+                        .isOk());
+
+    optional<vector<uint8_t>> optCredentialPubKey =
+            support::certificateChainGetTopMostKey(certChain[0].encodedCertificate);
+    ASSERT_TRUE(optCredentialPubKey);
+    *outCredentialPubKey = optCredentialPubKey.value();
+
+    size_t proofOfProvisioningSize = 106;
+    // Not in v1 HAL, may fail
+    wc->setExpectedProofOfProvisioningSize(proofOfProvisioningSize);
+
+    ASSERT_TRUE(wc->startPersonalization(1 /* numAccessControlProfiles */,
+                                         {1} /* numDataElementsPerNamespace */)
+                        .isOk());
+
+    // Access control profile 0: open access - don't care about the returned SACP
+    SecureAccessControlProfile sacp;
+    ASSERT_TRUE(wc->addAccessControlProfile(1, {}, false, 0, 0, &sacp).isOk());
+
+    // Single entry - don't care about the returned encrypted data
+    ASSERT_TRUE(wc->beginAddEntry({1}, "ns", "Some Data", 1).isOk());
+    vector<uint8_t> encryptedData;
+    ASSERT_TRUE(wc->addEntryValue({9}, &encryptedData).isOk());
+
+    vector<uint8_t> proofOfProvisioningSignature;
+    Status status = wc->finishAddingEntries(outCredentialData, &proofOfProvisioningSignature);
+    EXPECT_TRUE(status.isOk()) << status.exceptionCode() << ": " << status.exceptionMessage();
+}
+
+// This checks that any methods called on an IIdentityCredential obtained via a session
+// returns STATUS_FAILED except for startRetrieval(), startRetrieveEntryValue(),
+// retrieveEntryValue(), finishRetrieval(), setRequestedNamespaces(), setVerificationToken()
+//
+TEST_P(PresentationSessionTests, returnsFailureOnUnsupportedMethods) {
+    if (halApiVersion_ < 4) {
+        GTEST_SKIP() << "Need HAL API version 4, have " << halApiVersion_;
+    }
+
+    provisionData();
+
+    sp<IPresentationSession> session;
+    ASSERT_TRUE(credentialStore_
+                        ->createPresentationSession(
+                                CipherSuite::CIPHERSUITE_ECDHE_HKDF_ECDSA_WITH_AES_256_GCM_SHA256,
+                                &session)
+                        .isOk());
+
+    sp<IIdentityCredential> credential;
+    ASSERT_TRUE(session->getCredential(credential1Data_, &credential).isOk());
+
+    Status result;
+
+    vector<uint8_t> signatureProofOfDeletion;
+    result = credential->deleteCredential(&signatureProofOfDeletion);
+    EXPECT_EQ(binder::Status::EX_SERVICE_SPECIFIC, result.exceptionCode());
+    EXPECT_EQ(IIdentityCredentialStore::STATUS_FAILED, result.serviceSpecificErrorCode());
+
+    vector<uint8_t> ephemeralKeyPair;
+    result = credential->createEphemeralKeyPair(&ephemeralKeyPair);
+    EXPECT_EQ(binder::Status::EX_SERVICE_SPECIFIC, result.exceptionCode());
+    EXPECT_EQ(IIdentityCredentialStore::STATUS_FAILED, result.serviceSpecificErrorCode());
+
+    result = credential->setReaderEphemeralPublicKey({});
+    EXPECT_EQ(binder::Status::EX_SERVICE_SPECIFIC, result.exceptionCode());
+    EXPECT_EQ(IIdentityCredentialStore::STATUS_FAILED, result.serviceSpecificErrorCode());
+
+    int64_t authChallenge;
+    result = credential->createAuthChallenge(&authChallenge);
+    EXPECT_EQ(binder::Status::EX_SERVICE_SPECIFIC, result.exceptionCode());
+    EXPECT_EQ(IIdentityCredentialStore::STATUS_FAILED, result.serviceSpecificErrorCode());
+
+    Certificate certificate;
+    vector<uint8_t> signingKeyBlob;
+    result = credential->generateSigningKeyPair(&signingKeyBlob, &certificate);
+    EXPECT_EQ(binder::Status::EX_SERVICE_SPECIFIC, result.exceptionCode());
+    EXPECT_EQ(IIdentityCredentialStore::STATUS_FAILED, result.serviceSpecificErrorCode());
+
+    result = credential->deleteCredentialWithChallenge({}, &signatureProofOfDeletion);
+    EXPECT_EQ(binder::Status::EX_SERVICE_SPECIFIC, result.exceptionCode());
+    EXPECT_EQ(IIdentityCredentialStore::STATUS_FAILED, result.serviceSpecificErrorCode());
+
+    vector<uint8_t> signatureProofOfOwnership;
+    result = credential->proveOwnership({}, &signatureProofOfOwnership);
+    EXPECT_EQ(binder::Status::EX_SERVICE_SPECIFIC, result.exceptionCode());
+    EXPECT_EQ(IIdentityCredentialStore::STATUS_FAILED, result.serviceSpecificErrorCode());
+
+    sp<IWritableIdentityCredential> writableCredential;
+    result = credential->updateCredential(&writableCredential);
+    EXPECT_EQ(binder::Status::EX_SERVICE_SPECIFIC, result.exceptionCode());
+    EXPECT_EQ(IIdentityCredentialStore::STATUS_FAILED, result.serviceSpecificErrorCode());
+}
+
+// TODO: need to add tests to check that the returned IIdentityCredential works
+//       as intended.
+
+GTEST_ALLOW_UNINSTANTIATED_PARAMETERIZED_TEST(PresentationSessionTests);
+INSTANTIATE_TEST_SUITE_P(
+        Identity, PresentationSessionTests,
+        testing::ValuesIn(android::getAidlHalInstanceNames(IIdentityCredentialStore::descriptor)),
+        android::PrintInstanceNameToString);
+
+}  // namespace android::hardware::identity
diff --git a/security/keymint/aidl/vts/functional/KeyMintTest.cpp b/security/keymint/aidl/vts/functional/KeyMintTest.cpp
index 5b80b6f..d109058 100644
--- a/security/keymint/aidl/vts/functional/KeyMintTest.cpp
+++ b/security/keymint/aidl/vts/functional/KeyMintTest.cpp
@@ -4608,8 +4608,10 @@
     auto params = AuthorizationSetBuilder().BlockMode(BlockMode::ECB).Padding(PaddingMode::PKCS7);
 
     // Try various message lengths; all should work.
-    for (size_t i = 0; i < 32; ++i) {
-        string message(i, 'a');
+    for (size_t i = 0; i <= 48; i++) {
+        SCOPED_TRACE(testing::Message() << "i = " << i);
+        // Edge case: '\t' (0x09) is also a valid PKCS7 padding character.
+        string message(i, '\t');
         string ciphertext = EncryptMessage(message, params);
         EXPECT_EQ(i + 16 - (i % 16), ciphertext.size());
         string plaintext = DecryptMessage(ciphertext, params);
@@ -4633,7 +4635,7 @@
     auto params = AuthorizationSetBuilder().BlockMode(BlockMode::ECB).Padding(PaddingMode::PKCS7);
 
     // Try various message lengths; all should fail
-    for (size_t i = 0; i < 32; ++i) {
+    for (size_t i = 0; i <= 48; i++) {
         string message(i, 'a');
         EXPECT_EQ(ErrorCode::INCOMPATIBLE_PADDING_MODE, Begin(KeyPurpose::ENCRYPT, params));
     }
@@ -5775,8 +5777,8 @@
 
     ASSERT_GT(key_blob_.size(), 0U);
 
-    // Two-block message.
-    string message = "1234567890123456";
+    // Four-block message.
+    string message = "12345678901234561234567890123456";
     vector<uint8_t> iv1;
     string ciphertext1 = EncryptMessage(message, BlockMode::CBC, PaddingMode::NONE, &iv1);
     EXPECT_EQ(message.size(), ciphertext1.size());
@@ -5936,8 +5938,10 @@
                                                  .Padding(PaddingMode::PKCS7)));
 
     // Try various message lengths; all should work.
-    for (size_t i = 0; i < 32; ++i) {
-        string message(i, 'a');
+    for (size_t i = 0; i <= 32; i++) {
+        SCOPED_TRACE(testing::Message() << "i = " << i);
+        // Edge case: '\t' (0x09) is also a valid PKCS7 padding character, albeit not for 3DES.
+        string message(i, '\t');
         vector<uint8_t> iv;
         string ciphertext = EncryptMessage(message, BlockMode::CBC, PaddingMode::PKCS7, &iv);
         EXPECT_EQ(i + 8 - (i % 8), ciphertext.size());
@@ -5959,7 +5963,7 @@
                                                  .Padding(PaddingMode::NONE)));
 
     // Try various message lengths; all should fail.
-    for (size_t i = 0; i < 32; ++i) {
+    for (size_t i = 0; i <= 32; i++) {
         auto begin_params =
                 AuthorizationSetBuilder().BlockMode(BlockMode::CBC).Padding(PaddingMode::PKCS7);
         EXPECT_EQ(ErrorCode::INCOMPATIBLE_PADDING_MODE, Begin(KeyPurpose::ENCRYPT, begin_params));
@@ -5990,6 +5994,7 @@
                                 .Authorization(TAG_NONCE, iv);
 
     for (size_t i = 0; i < kMaxPaddingCorruptionRetries; ++i) {
+        SCOPED_TRACE(testing::Message() << "i = " << i);
         ++ciphertext[ciphertext.size() / 2];
         EXPECT_EQ(ErrorCode::OK, Begin(KeyPurpose::DECRYPT, begin_params));
         string plaintext;