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()

2 files changed, 13 insertions, 2 deletions

diff --git a/src/lib/tls/tls_cbc/tls_cbc.cpp b/src/lib/tls/tls_cbc/tls_cbc.cpp
index ef397e44d..bd9ce2528 100644
--- a/src/lib/tls/tls_cbc/tls_cbc.cpp
+++ b/src/lib/tls/tls_cbc/tls_cbc.cpp
@@ -1,8 +1,9 @@
 /*
 * TLS CBC Record Handling
 * (C) 2012,2013,2014,2015,2016 Jack Lloyd
-*     2016 Juraj Somorovsky
-*     2016 Matthias Gierlings
+* (C) 2016 Juraj Somorovsky
+* (C) 2016 Matthias Gierlings
+* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -46,7 +47,14 @@ void TLS_CBC_HMAC_AEAD_Mode::clear()
    {
    cipher().clear();
    mac().clear();
+   reset();
+   }
+
+void TLS_CBC_HMAC_AEAD_Mode::reset()
+   {
    cbc_state().clear();
+   m_ad.clear();
+   m_msg.clear();
    }
 
 std::string TLS_CBC_HMAC_AEAD_Mode::name() const
diff --git a/src/lib/tls/tls_cbc/tls_cbc.h b/src/lib/tls/tls_cbc/tls_cbc.h
index 846774998..c448879fb 100644
--- a/src/lib/tls/tls_cbc/tls_cbc.h
+++ b/src/lib/tls/tls_cbc/tls_cbc.h
@@ -1,6 +1,7 @@
 /*
 * TLS CBC+HMAC AEAD
 * (C) 2016 Jack Lloyd
+* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -41,6 +42,8 @@ class TLS_CBC_HMAC_AEAD_Mode : public AEAD_Mode
 
       void clear() override final;
 
+      void reset() override final;
+
  protected:
       TLS_CBC_HMAC_AEAD_Mode(const std::string& cipher_name,
                              size_t cipher_keylen,