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/*
* ARC4
* (C) 1999-2007 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#include <botan/arc4.h>
#include <botan/internal/xor_buf.h>
#include <botan/parsing.h>
namespace Botan {
/*
* Combine cipher stream with message
*/
void ARC4::cipher(const byte in[], byte out[], size_t length)
{
while(length >= buffer.size() - position)
{
xor_buf(out, in, &buffer[position], buffer.size() - position);
length -= (buffer.size() - position);
in += (buffer.size() - position);
out += (buffer.size() - position);
generate();
}
xor_buf(out, in, &buffer[position], length);
position += length;
}
/*
* Generate cipher stream
*/
void ARC4::generate()
{
byte SX, SY;
for(size_t i = 0; i != buffer.size(); i += 4)
{
SX = state[X+1]; Y = (Y + SX) % 256; SY = state[Y];
state[X+1] = SY; state[Y] = SX;
buffer[i] = state[(SX + SY) % 256];
SX = state[X+2]; Y = (Y + SX) % 256; SY = state[Y];
state[X+2] = SY; state[Y] = SX;
buffer[i+1] = state[(SX + SY) % 256];
SX = state[X+3]; Y = (Y + SX) % 256; SY = state[Y];
state[X+3] = SY; state[Y] = SX;
buffer[i+2] = state[(SX + SY) % 256];
X = (X + 4) % 256;
SX = state[X]; Y = (Y + SX) % 256; SY = state[Y];
state[X] = SY; state[Y] = SX;
buffer[i+3] = state[(SX + SY) % 256];
}
position = 0;
}
/*
* ARC4 Key Schedule
*/
void ARC4::key_schedule(const byte key[], u32bit length)
{
clear();
for(size_t i = 0; i != 256; ++i)
state[i] = i;
for(size_t i = 0, state_index = 0; i != 256; ++i)
{
state_index = (state_index + key[i % length] + state[i]) % 256;
std::swap(state[i], state[state_index]);
}
for(size_t i = 0; i <= SKIP; i += buffer.size())
generate();
position += (SKIP % buffer.size());
}
/*
* Return the name of this type
*/
std::string ARC4::name() const
{
if(SKIP == 0) return "ARC4";
if(SKIP == 256) return "MARK-4";
else return "RC4_skip(" + to_string(SKIP) + ")";
}
/*
* Clear memory of sensitive data
*/
void ARC4::clear()
{
zeroise(state);
zeroise(buffer);
position = X = Y = 0;
}
/*
* ARC4 Constructor
*/
ARC4::ARC4(size_t s) : StreamCipher(1, 256), SKIP(s),
state(256), buffer(DEFAULT_BUFFERSIZE)
{
clear();
}
}
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