Convert CFB to Transformation API

1 files changed, 150 insertions, 0 deletions

diff --git a/src/modes/cfb/cfb.cpp b/src/modes/cfb/cfb.cpp
new file mode 100644
index 000000000..2edb917b4
--- /dev/null
+++ b/src/modes/cfb/cfb.cpp
@@ -0,0 +1,150 @@
+/*
+* CFB Mode
+* (C) 1999-2007,2013 Jack Lloyd
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/cfb.h>
+#include <botan/parsing.h>
+#include <botan/internal/xor_buf.h>
+
+namespace Botan {
+
+CFB_Mode::CFB_Mode(BlockCipher* cipher, size_t feedback_bits) :
+   m_cipher(cipher),
+   m_feedback_bytes(feedback_bits ? feedback_bits / 8 : cipher->block_size())
+   {
+   if(feedback_bits % 8 || feedback() > cipher->block_size())
+      throw std::invalid_argument(name() + ": feedback bits " +
+                                  std::to_string(feedback_bits) + " not supported");
+   }
+
+void CFB_Mode::clear()
+   {
+   m_cipher->clear();
+   m_shift_register.clear();
+   }
+
+std::string CFB_Mode::name() const
+   {
+   if(feedback() == cipher().block_size())
+      return cipher().name() + "/CFB";
+   else
+      return cipher().name() + "/CFB(" + std::to_string(feedback()*8) + ")";
+   }
+
+size_t CFB_Mode::output_length(size_t input_length) const
+   {
+   return input_length;
+   }
+
+size_t CFB_Mode::update_granularity() const
+   {
+   return feedback();
+   }
+
+size_t CFB_Mode::minimum_final_size() const
+   {
+   return 0;
+   }
+
+Key_Length_Specification CFB_Mode::key_spec() const
+   {
+   return cipher().key_spec();
+   }
+
+size_t CFB_Mode::default_nonce_size() const
+   {
+   return cipher().block_size();
+   }
+
+bool CFB_Mode::valid_nonce_length(size_t n) const
+   {
+   return (n == cipher().block_size());
+   }
+
+void CFB_Mode::key_schedule(const byte key[], size_t length)
+   {
+   m_cipher->set_key(key, length);
+   }
+
+secure_vector<byte> CFB_Mode::start(const byte nonce[], size_t nonce_len)
+   {
+   if(!valid_nonce_length(nonce_len))
+      throw Invalid_IV_Length(name(), nonce_len);
+
+   m_shift_register.assign(nonce, nonce + nonce_len);
+   m_keystream_buf.resize(m_shift_register.size());
+   cipher().encrypt(m_shift_register, m_keystream_buf);
+
+   return secure_vector<byte>();
+   }
+
+void CFB_Encryption::update(secure_vector<byte>& buffer, size_t offset)
+   {
+   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
+   size_t sz = buffer.size() - offset;
+   byte* buf = &buffer[offset];
+
+   const size_t BS = cipher().block_size();
+
+   secure_vector<byte>& state = shift_register();
+   const size_t shift = feedback();
+
+   while(sz)
+      {
+      const size_t took = std::min(shift, sz);
+      xor_buf(&buf[0], &keystream_buf()[0], took);
+
+      // Assumes feedback-sized block except for last input
+      copy_mem(&state[0], &state[shift], BS - shift);
+      copy_mem(&state[BS-shift], &buf[0], shift);
+      cipher().encrypt(state, keystream_buf());
+
+      buf += took;
+      sz -= took;
+      }
+   }
+
+void CFB_Encryption::finish(secure_vector<byte>& buffer, size_t offset)
+   {
+   update(buffer, offset);
+   }
+
+void CFB_Decryption::update(secure_vector<byte>& buffer, size_t offset)
+   {
+   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");
+   size_t sz = buffer.size() - offset;
+   byte* buf = &buffer[offset];
+
+   const size_t BS = cipher().block_size();
+
+   secure_vector<byte>& state = shift_register();
+   const size_t shift = feedback();
+
+   while(sz)
+      {
+      const size_t took = std::min(shift, sz);
+
+      // first update shift register with ciphertext
+      copy_mem(&state[0], &state[shift], BS - shift);
+      copy_mem(&state[BS-shift], &buf[0], took);
+
+      // then decrypt
+      xor_buf(&buf[0], &keystream_buf()[0], took);
+
+      // then update keystream
+      cipher().encrypt(state, keystream_buf());
+
+      buf += took;
+      sz -= took;
+      }
+   }
+
+void CFB_Decryption::finish(secure_vector<byte>& buffer, size_t offset)
+   {
+   update(buffer, offset);
+   }
+
+}