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/* salsa20-crypt.c
*
* The Salsa20 stream cipher.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2012 Simon Josefsson
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02111-1301, USA.
*/
/* Based on:
salsa20-ref.c version 20051118
D. J. Bernstein
Public domain.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <string.h>
#include "salsa20.h"
#include "macros.h"
#include "memxor.h"
#ifdef WORDS_BIGENDIAN
#define LE_SWAP32(v) \
((ROTL32(8, v) & 0x00FF00FFUL) | \
(ROTL32(24, v) & 0xFF00FF00UL))
#else
#define LE_SWAP32(v) (v)
#endif
#define QROUND(x0, x1, x2, x3) do { \
x1 ^= ROTL32(7, x0 + x3); \
x2 ^= ROTL32(9, x1 + x0); \
x3 ^= ROTL32(13, x2 + x1); \
x0 ^= ROTL32(18, x3 + x2); \
} while(0)
void
salsa20_crypt(struct salsa20_ctx *ctx,
unsigned length,
uint8_t *c,
const uint8_t *m)
{
if (!length)
return;
for (;;)
{
uint32_t x[_SALSA20_INPUT_LENGTH];
int i;
memcpy (x, ctx->input, sizeof(x));
for (i = 0;i < 10;i ++)
{
QROUND(x[0], x[4], x[8], x[12]);
QROUND(x[5], x[9], x[13], x[1]);
QROUND(x[10], x[14], x[2], x[6]);
QROUND(x[15], x[3], x[7], x[11]);
QROUND(x[0], x[1], x[2], x[3]);
QROUND(x[5], x[6], x[7], x[4]);
QROUND(x[10], x[11], x[8], x[9]);
QROUND(x[15], x[12], x[13], x[14]);
}
for (i = 0;i < _SALSA20_INPUT_LENGTH;++i)
{
uint32_t t = x[i] + ctx->input[i];
x[i] = LE_SWAP32 (t);
}
ctx->input[9] += (++ctx->input[8] == 0);
/* stopping at 2^70 length per nonce is user's responsibility */
if (length <= SALSA20_BLOCK_SIZE)
{
memxor3 (c, m, (uint8_t *) x, length);
return;
}
memxor3 (c, m, (uint8_t *) x, SALSA20_BLOCK_SIZE);
length -= SALSA20_BLOCK_SIZE;
c += SALSA20_BLOCK_SIZE;
m += SALSA20_BLOCK_SIZE;
}
}
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