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/*************************************************
* ARC4 Source File *
* (C) 1999-2005 The Botan Project *
*************************************************/
#include <botan/arc4.h>
#include <botan/bit_ops.h>
#include <botan/parsing.h>
namespace Botan {
/*************************************************
* Combine cipher stream with message *
*************************************************/
void ARC4::cipher(const byte in[], byte out[], u32bit length)
{
while(length >= buffer.size() - position)
{
xor_buf(out, in, buffer.begin() + position, buffer.size() - position);
length -= (buffer.size() - position);
in += (buffer.size() - position);
out += (buffer.size() - position);
generate();
}
xor_buf(out, in, buffer.begin() + position, length);
position += length;
}
/*************************************************
* Generate cipher stream *
*************************************************/
void ARC4::generate()
{
u32bit SX, SY;
for(u32bit j = 0; j != buffer.size(); j += 4)
{
SX = state[X+1]; Y = (Y + SX) % 256; SY = state[Y];
state[X+1] = SY; state[Y] = SX;
buffer[j] = state[(SX + SY) % 256];
SX = state[X+2]; Y = (Y + SX) % 256; SY = state[Y];
state[X+2] = SY; state[Y] = SX;
buffer[j+1] = state[(SX + SY) % 256];
SX = state[X+3]; Y = (Y + SX) % 256; SY = state[Y];
state[X+3] = SY; state[Y] = SX;
buffer[j+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[j+3] = state[(SX + SY) % 256];
}
position = 0;
}
/*************************************************
* ARC4 Key Schedule *
*************************************************/
void ARC4::key(const byte key[], u32bit length)
{
clear();
for(u32bit j = 0; j != 256; j++)
state[j] = j;
for(u32bit j = 0, state_index = 0; j != 256; j++)
{
state_index = (state_index + key[j % length] + state[j]) % 256;
std::swap(state[j], state[state_index]);
}
for(u32bit j = 0; j <= SKIP; j += 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() throw()
{
state.clear();
buffer.clear();
position = X = Y = 0;
}
/*************************************************
* ARC4 Constructor *
*************************************************/
// monotone-specific: max keysize is 256 bytes
ARC4::ARC4(u32bit s) : StreamCipher(1, 256), SKIP(s)
{
clear();
}
}
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