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, 8 insertions, 1 deletions

diff --git a/src/lib/modes/stream_mode.h b/src/lib/modes/stream_mode.h
index 3a0c8574c..83b0543c9 100644
--- a/src/lib/modes/stream_mode.h
+++ b/src/lib/modes/stream_mode.h
@@ -1,5 +1,6 @@
 /*
 * (C) 2015 Jack Lloyd
+* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -44,7 +45,13 @@ class BOTAN_DLL Stream_Cipher_Mode : public Cipher_Mode
 
       std::string name() const override { return m_cipher->name(); }
 
-      void clear() override { return m_cipher->clear(); }
+      void clear() override
+         {
+         m_cipher->clear();
+         reset();
+         }
+
+      void reset() override { /* no msg state */ return; }
 
    private:
       void start_msg(const byte nonce[], size_t nonce_len) override