Add HmacSHA256 backed by AndroidKeyStore.

This also adds the MAC length constraint on imported HMAC keys. HMAC
doesn't work without this constraint at the moment.

Bug: 18088752
Change-Id: I8613f58f5d2a84df00bcf6179d13e30619440330

1 files changed, 14 insertions, 0 deletions

diff --git a/keystore/java/android/security/KeyStoreKeyConstraints.java b/keystore/java/android/security/KeyStoreKeyConstraints.java
index 47bb1ccbbeb7..b5e2436dc0cf 100644
--- a/keystore/java/android/security/KeyStoreKeyConstraints.java
+++ b/keystore/java/android/security/KeyStoreKeyConstraints.java
@@ -401,6 +401,20 @@ public abstract class KeyStoreKeyConstraints {
                     throw new IllegalArgumentException("Unknown digest: " + digest);
             }
         }
+
+        /**
+         * @hide
+         */
+        public static Integer getOutputSizeBytes(@DigestEnum int digest) {
+            switch (digest) {
+                case NONE:
+                    return null;
+                case SHA256:
+                    return 256 / 8;
+                default:
+                    throw new IllegalArgumentException("Unknown digest: " + digest);
+            }
+        }
     }
 
     @Retention(RetentionPolicy.SOURCE)