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, 10 insertions, 0 deletions

diff --git a/src/lib/modes/cfb/cfb.cpp b/src/lib/modes/cfb/cfb.cpp
index 793bfaf46..2d1477e27 100644
--- a/src/lib/modes/cfb/cfb.cpp
+++ b/src/lib/modes/cfb/cfb.cpp
@@ -1,6 +1,7 @@
 /*
 * CFB Mode
 * (C) 1999-2007,2013 Jack Lloyd
+* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -22,7 +23,13 @@ CFB_Mode::CFB_Mode(BlockCipher* cipher, size_t feedback_bits) :
 void CFB_Mode::clear()
    {
    m_cipher->clear();
+   reset();
+   }
+
+void CFB_Mode::reset()
+   {
    m_shift_register.clear();
+   m_keystream_buf.clear();
    }
 
 std::string CFB_Mode::name() const
diff --git a/src/lib/modes/cfb/cfb.h b/src/lib/modes/cfb/cfb.h
index 318bdab64..18611f3f2 100644
--- a/src/lib/modes/cfb/cfb.h
+++ b/src/lib/modes/cfb/cfb.h
@@ -1,6 +1,7 @@
 /*
 * CFB mode
 * (C) 1999-2007,2013 Jack Lloyd
+* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
@@ -34,6 +35,8 @@ class BOTAN_DLL CFB_Mode : public Cipher_Mode
       bool valid_nonce_length(size_t n) const override;
 
       void clear() override;
+
+      void reset() override;
    protected:
       CFB_Mode(BlockCipher* cipher, size_t feedback_bits);