rc4.cpp

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/*
* RC4
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/internal/rc4.h>
 
#include <botan/exceptn.h>
#include <botan/mem_ops.h>
 
namespace Botan {
 
/*
* Combine cipher stream with message
*/
void RC4::cipher_bytes(const uint8_t in[], uint8_t out[], size_t length) {
   assert_key_material_set();
 
   while(length >= m_buffer.size() - m_position) {
      xor_buf(out, in, &m_buffer[m_position], m_buffer.size() - m_position);
      length -= (m_buffer.size() - m_position);
      in += (m_buffer.size() - m_position);
      out += (m_buffer.size() - m_position);
      generate();
   }
   xor_buf(out, in, &m_buffer[m_position], length);
   m_position += length;
}
 
std::unique_ptr<StreamCipher> RC4::new_object() const {
   return std::make_unique<RC4>(m_SKIP);
}
 
size_t RC4::buffer_size() const {
   return 256;
}
 
Key_Length_Specification RC4::key_spec() const {
   return Key_Length_Specification(1, 256);
}
 
void RC4::set_iv_bytes(const uint8_t* /*iv*/, size_t length) {
   if(length > 0) {
      throw Invalid_IV_Length("RC4", length);
   }
}
 
/*
* Generate cipher stream
*/
void RC4::generate() {
   uint8_t SX, SY;
   for(size_t i = 0; i != m_buffer.size(); i += 4) {
      SX = m_state[m_X + 1];
      m_Y = (m_Y + SX) % 256;
      SY = m_state[m_Y];
      m_state[m_X + 1] = SY;
      m_state[m_Y] = SX;
      m_buffer[i] = m_state[(SX + SY) % 256];
 
      SX = m_state[m_X + 2];
      m_Y = (m_Y + SX) % 256;
      SY = m_state[m_Y];
      m_state[m_X + 2] = SY;
      m_state[m_Y] = SX;
      m_buffer[i + 1] = m_state[(SX + SY) % 256];
 
      SX = m_state[m_X + 3];
      m_Y = (m_Y + SX) % 256;
      SY = m_state[m_Y];
      m_state[m_X + 3] = SY;
      m_state[m_Y] = SX;
      m_buffer[i + 2] = m_state[(SX + SY) % 256];
 
      m_X = (m_X + 4) % 256;
      SX = m_state[m_X];
      m_Y = (m_Y + SX) % 256;
      SY = m_state[m_Y];
      m_state[m_X] = SY;
      m_state[m_Y] = SX;
      m_buffer[i + 3] = m_state[(SX + SY) % 256];
   }
   m_position = 0;
}
 
bool RC4::has_keying_material() const {
   return !m_state.empty();
}
 
/*
* RC4 Key Schedule
*/
void RC4::key_schedule(std::span<const uint8_t> key) {
   m_state.resize(256);
   m_buffer.resize(256);
 
   m_position = m_X = m_Y = 0;
 
   for(size_t i = 0; i != 256; ++i) {
      m_state[i] = static_cast<uint8_t>(i);
   }
 
   for(size_t i = 0, state_index = 0; i != 256; ++i) {
      state_index = (state_index + key[i % key.size()] + m_state[i]) % 256;
      std::swap(m_state[i], m_state[state_index]);
   }
 
   for(size_t i = 0; i <= m_SKIP; i += m_buffer.size()) {
      generate();
   }
 
   m_position += (m_SKIP % m_buffer.size());
}
 
/*
* Return the name of this type
*/
std::string RC4::name() const {
   if(m_SKIP == 0) {
      return "RC4";
   } else if(m_SKIP == 256) {
      return "MARK-4";
   } else {
      return "RC4(" + std::to_string(m_SKIP) + ")";
   }
}
 
/*
* Clear memory of sensitive data
*/
void RC4::clear() {
   zap(m_state);
   zap(m_buffer);
   m_position = m_X = m_Y = 0;
}
 
/*
* RC4 Constructor
*/
RC4::RC4(size_t s) : m_SKIP(s) {}
 
void RC4::seek(uint64_t /*offset*/) {
   throw Not_Implemented("RC4 does not support seeking");
}
}  // namespace Botan