Added SavableDigest

Author: dghgit

core/src/main/java/org/bouncycastle/crypto/SavableDigest.java

@@ -0,0 +1,13 @@
+package org.bouncycastle.crypto;
+
+import org.bouncycastle.crypto.digests.EncodableDigest;
+import org.bouncycastle.util.Memoable;
+
+/**
+ * Extended digest which provides the ability to store state and
+ * provide an encoding.
+ */
+public interface SavableDigest
+    extends ExtendedDigest, EncodableDigest, Memoable
+{
+}

core/src/main/java/org/bouncycastle/crypto/digests/SHA256Digest.java

@@ -4,6 +4,7 @@
 import org.bouncycastle.crypto.CryptoServiceProperties;
 import org.bouncycastle.crypto.CryptoServicePurpose;
 import org.bouncycastle.crypto.CryptoServicesRegistrar;
+import org.bouncycastle.crypto.SavableDigest;
 import org.bouncycastle.util.Memoable;
 import org.bouncycastle.util.Pack;
 
@@ -21,7 +22,7 @@
  */
 public class SHA256Digest
     extends GeneralDigest
-    implements EncodableDigest
+    implements SavableDigest
 {
     private static final int    DIGEST_LENGTH = 32;