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/*
* Copyright (C) 2008 D. J. Bernstein (dedicated to the public domain)
* Copyright (C) 2015 René Kijewski <rene.kijewski@fu-berlin.de>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
/*
* Please notice:
* - This implementation of the ChaCha stream cipher is very stripped down.
* - It assumes a little-endian system.
* - It is implemented for little code and data size, but will likely be
* slower than the refenrence implementation. Optimized implementation will
* out-perform the code even more.
*/
#include "crypto/chacha.h"
#include "byteorder.h"
#if __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
# error "This code is implementented in a way that it will only work for little-endian systems!"
#endif
#include <string.h>
static void _r(uint32_t *d, uint32_t *a, const uint32_t *b, unsigned c)
{
*a += *b;
uint32_t tmp = *a ^ *d;
*d = (tmp << c) | (tmp >> (32 - c));
}
static void _doubleround(void *output_, const uint32_t input[16], uint8_t rounds)
{
uint32_t *output = (uint32_t *) output_;
memcpy(output, input, 64);
rounds *= 4;
for (unsigned i = 0; i < rounds; ++i) {
uint32_t *a = &output[((i + ((i & 4) ? 0 : 0)) & 3) + (4 * 0)];
uint32_t *b = &output[((i + ((i & 4) ? 1 : 0)) & 3) + (4 * 1)];
uint32_t *c = &output[((i + ((i & 4) ? 2 : 0)) & 3) + (4 * 2)];
uint32_t *d = &output[((i + ((i & 4) ? 3 : 0)) & 3) + (4 * 3)];
_r(d, a, b, 16);
_r(b, c, d, 12);
_r(d, a, b, 8);
_r(b, c, d, 7);
}
for (unsigned i = 0; i < 16; ++i) {
output[i] += input[i];
}
}
int chacha_init(chacha_ctx *ctx,
unsigned rounds,
const uint8_t *key, uint32_t keylen,
const uint8_t nonce[8])
{
if (keylen == 32) {
memcpy(ctx->state + 0, "expand 32-byte k", 16);
memcpy(ctx->state + 4, key, 32);
}
else if (keylen == 16) {
memcpy(ctx->state + 0, "expand 16-byte k", 16);
memcpy(ctx->state + 4, key, 16);
memcpy(ctx->state + 8, key, 16);
}
else {
return -1;
}
if ((rounds == 20) || (rounds == 12) || (rounds == 8)) {
ctx->rounds = rounds;
}
else {
return -1;
}
memset(ctx->state + 12, 0, 8);
memcpy(ctx->state + 14, nonce, 8);
return 0;
}
void chacha_keystream_bytes(chacha_ctx *ctx, void *x)
{
_doubleround(x, ctx->state, ctx->rounds);
++ctx->state[12];
if (ctx->state[12] == 0) {
++ctx->state[13];
}
}
void chacha_encrypt_bytes(chacha_ctx *ctx, const uint8_t *m, uint8_t *c)
{
uint8_t x[64];
chacha_keystream_bytes(ctx, x);
for (unsigned i = 0 ; i < 64; ++i) {
c[i] = m[i] ^ x[i];
}
}
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