Cipher_Mode and AEAD_Mode improvements

See PR #552

- Add Cipher_Mode::reset() which resets just the message specific state and allows encrypting again under the existing key
- In Cipher_Mode::clear() (at some planes) use cipher->clear() instead of resetting the pointer which would make the cipher object unusable
- EAX_Decryption::output_length() bugfix?! Now its possible to decrypt an empty ciphertext (just a tag)
- Bugfix for GCM_Decryption::finish()
- set tag length in GCM_Mode::name()
- Cipher_Mode tests: add tests for reset()and process()
- AEAD_Mode tests: add tests for reset(), clear(), update() and process()

1 files changed, 10 insertions, 1 deletions

diff --git a/src/lib/modes/cipher_mode.h b/src/lib/modes/cipher_mode.h
index 7c0f8fc57..8bf58f10a 100644
--- a/src/lib/modes/cipher_mode.h
+++ b/src/lib/modes/cipher_mode.h
@@ -65,7 +65,7 @@ class BOTAN_DLL Cipher_Mode
       *
       * Processes msg in place and returns bytes written. Normally
       * this will be either msg_len (indicating the entire message was
-      * processes) or for certain AEAD modes zero (indicating that the
+      * processed) or for certain AEAD modes zero (indicating that the
       * mode requires the entire message be processed in one pass).
       *
       * @param msg the message to be processed
@@ -127,9 +127,18 @@ class BOTAN_DLL Cipher_Mode
 
       virtual std::string name() const = 0;
 
+      /**
+      * Zeroise all state
+      * See also reset_msg()
+      */
       virtual void clear() = 0;
 
       /**
+      * Resets just the message specific state and allows encrypting again under the existing key
+      */
+      virtual void reset() = 0;
+
+      /**
       * @return true iff this mode provides authentication as well as
       * confidentiality.
       */