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/*
* RC4
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/rc4.h>
namespace Botan {
RC4* RC4::make(const Spec& spec)
{
if(spec.algo_name() == "RC4")
return new RC4(spec.arg_as_integer(0, 0));
if(spec.algo_name() == "RC4_drop")
return new RC4(768);
return nullptr;
}
/*
* Combine cipher stream with message
*/
void RC4::cipher(const byte in[], byte out[], size_t length)
{
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;
}
/*
* Generate cipher stream
*/
void RC4::generate()
{
byte 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;
}
/*
* RC4 Key Schedule
*/
void RC4::key_schedule(const byte key[], size_t length)
{
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<byte>(i);
for(size_t i = 0, state_index = 0; i != 256; ++i)
{
state_index = (state_index + key[i % length] + 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";
if(m_SKIP == 256) return "MARK-4";
else return "RC4_skip(" + 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(u64bit)
{
throw Exception("RC4 does not support seeking");
}
}
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