Identity: Update requirements about SessionTranscript CBOR and provisioning challenge.

Bug: 156911917
Bug: 158107945
Test: atest VtsHalIdentityTargetTest
Test: atest android.security.identity.cts
Change-Id: Iacdf89744bbd30c5a10d6cba873147e424ddb01b

2 files changed, 12 insertions, 23 deletions

diff --git a/identity/java/android/security/identity/IdentityCredential.java b/identity/java/android/security/identity/IdentityCredential.java
index b351b3d77430..493c85a930be 100644
--- a/identity/java/android/security/identity/IdentityCredential.java
+++ b/identity/java/android/security/identity/IdentityCredential.java
@@ -167,25 +167,14 @@ public abstract class IdentityCredential {
      *   IntentToRetain = bool
      * </pre>
      *
-     * <p>If the {@code sessionTranscript} parameter is not {@code null}, it must contain CBOR
-     * data conforming to the following CDDL schema:
-     *
-     * <pre>
-     *   SessionTranscript = [
-     *     DeviceEngagementBytes,
-     *     EReaderKeyBytes
-     *   ]
-     *
-     *   DeviceEngagementBytes = #6.24(bstr .cbor DeviceEngagement)  ; Bytes of DeviceEngagement
-     *   EReaderKeyBytes = #6.24(bstr .cbor EReaderKey.Pub)  ; Bytes of EReaderKey.pub
-     *
-     *   EReaderKey.Pub = COSE_Key    ; Ephemeral public key provided by reader
-     * </pre>
-     *
-     * <p>where a {@code COSE_Key} structure for the public part of the key-pair previously
-     * generated by {@link #createEphemeralKeyPair()} must appear somewhere in
-     * {@code DeviceEngagement} and the X and Y coordinates must both be present
-     * in uncompressed form.
+     * <p>If the {@code sessionTranscript} parameter is not {@code null}, the X and Y coordinates
+     * of the public part of the key-pair previously generated by {@link #createEphemeralKeyPair()}
+     * must appear somewhere in the bytes of the CBOR. Each of these coordinates must appear
+     * encoded with the most significant bits first and use the exact amount of bits indicated by
+     * the key size of the ephemeral keys. For example, if the ephemeral key is using the P-256
+     * curve then the 32 bytes for the X coordinate encoded with the most significant bits first
+     * must appear somewhere in {@code sessionTranscript} and ditto for the 32 bytes for the Y
+     * coordinate.
      *
      * <p>If {@code readerAuth} is not {@code null} it must be the bytes of a {@code COSE_Sign1}
      * structure as defined in RFC 8152. For the payload nil shall be used and the
diff --git a/identity/java/android/security/identity/WritableIdentityCredential.java b/identity/java/android/security/identity/WritableIdentityCredential.java
index c7aa32855abc..305d0ead0652 100644
--- a/identity/java/android/security/identity/WritableIdentityCredential.java
+++ b/identity/java/android/security/identity/WritableIdentityCredential.java
@@ -56,10 +56,10 @@ public abstract class WritableIdentityCredential {
      * authority doesn't care about the nature of the security hardware. If called, however, this
      * method must be called before {@link #personalize(PersonalizationData)}.
      *
-     * @param challenge is a byte array whose contents should be unique, fresh and provided by
-     *                  the issuing authority. The value provided is embedded in the attestation
-     *                  extension and enables the issuing authority to verify that the attestation
-     *                  certificate is fresh.
+     * @param challenge is a non-empty byte array whose contents should be unique, fresh and
+     *                  provided by the issuing authority. The value provided is embedded in the
+     *                  attestation extension and enables the issuing authority to verify that the
+     *                  attestation certificate is fresh.
      * @return the X.509 certificate for this credential's CredentialKey.
      */
     public abstract @NonNull Collection<X509Certificate> getCredentialKeyCertificateChain(