salsa20.c 5.42 KB
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/* salsa20.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., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/* Based on:
   salsa20-ref.c version 20051118
   D. J. Bernstein
   Public domain.
*/

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>

#include "salsa20.h"

#define ROTL32(x,n) ((((x))<<(n)) | (((x))>>(32-(n))))

#define SWAP32(v)				\
  ((ROTL32(v,  8) & 0x00FF00FFUL) |		\
   (ROTL32(v, 24) & 0xFF00FF00UL))

#ifdef WORDS_BIGENDIAN
#define U32TO32_LITTLE(v) SWAP32(v)
#else
#define U32TO32_LITTLE(v) (v)
#endif

#define U8TO32_LITTLE(p) U32TO32_LITTLE(((uint32_t*)(p))[0])
#define U32TO8_LITTLE(p, v) (((uint32_t*)(p))[0] = U32TO32_LITTLE(v))

/*
salsa20-ref.c version 20051118
D. J. Bernstein
Public domain.
*/

#define ROTATE(v,c) (ROTL32(v,c))
#define XOR(v,w) ((v) ^ (w))
#define PLUS(v,w) ((v) + (w))
#define PLUSONE(v) (PLUS((v),1))

static void salsa20_wordtobyte(uint8_t output[64],const uint32_t input[16])
{
  uint32_t x[16];
  int i;

  for (i = 0;i < 16;++i) x[i] = input[i];
  for (i = 20;i > 0;i -= 2) {
    x[ 4] = XOR(x[ 4],ROTATE(PLUS(x[ 0],x[12]), 7));
    x[ 8] = XOR(x[ 8],ROTATE(PLUS(x[ 4],x[ 0]), 9));
    x[12] = XOR(x[12],ROTATE(PLUS(x[ 8],x[ 4]),13));
    x[ 0] = XOR(x[ 0],ROTATE(PLUS(x[12],x[ 8]),18));
    x[ 9] = XOR(x[ 9],ROTATE(PLUS(x[ 5],x[ 1]), 7));
    x[13] = XOR(x[13],ROTATE(PLUS(x[ 9],x[ 5]), 9));
    x[ 1] = XOR(x[ 1],ROTATE(PLUS(x[13],x[ 9]),13));
    x[ 5] = XOR(x[ 5],ROTATE(PLUS(x[ 1],x[13]),18));
    x[14] = XOR(x[14],ROTATE(PLUS(x[10],x[ 6]), 7));
    x[ 2] = XOR(x[ 2],ROTATE(PLUS(x[14],x[10]), 9));
    x[ 6] = XOR(x[ 6],ROTATE(PLUS(x[ 2],x[14]),13));
    x[10] = XOR(x[10],ROTATE(PLUS(x[ 6],x[ 2]),18));
    x[ 3] = XOR(x[ 3],ROTATE(PLUS(x[15],x[11]), 7));
    x[ 7] = XOR(x[ 7],ROTATE(PLUS(x[ 3],x[15]), 9));
    x[11] = XOR(x[11],ROTATE(PLUS(x[ 7],x[ 3]),13));
    x[15] = XOR(x[15],ROTATE(PLUS(x[11],x[ 7]),18));
    x[ 1] = XOR(x[ 1],ROTATE(PLUS(x[ 0],x[ 3]), 7));
    x[ 2] = XOR(x[ 2],ROTATE(PLUS(x[ 1],x[ 0]), 9));
    x[ 3] = XOR(x[ 3],ROTATE(PLUS(x[ 2],x[ 1]),13));
    x[ 0] = XOR(x[ 0],ROTATE(PLUS(x[ 3],x[ 2]),18));
    x[ 6] = XOR(x[ 6],ROTATE(PLUS(x[ 5],x[ 4]), 7));
    x[ 7] = XOR(x[ 7],ROTATE(PLUS(x[ 6],x[ 5]), 9));
    x[ 4] = XOR(x[ 4],ROTATE(PLUS(x[ 7],x[ 6]),13));
    x[ 5] = XOR(x[ 5],ROTATE(PLUS(x[ 4],x[ 7]),18));
    x[11] = XOR(x[11],ROTATE(PLUS(x[10],x[ 9]), 7));
    x[ 8] = XOR(x[ 8],ROTATE(PLUS(x[11],x[10]), 9));
    x[ 9] = XOR(x[ 9],ROTATE(PLUS(x[ 8],x[11]),13));
    x[10] = XOR(x[10],ROTATE(PLUS(x[ 9],x[ 8]),18));
    x[12] = XOR(x[12],ROTATE(PLUS(x[15],x[14]), 7));
    x[13] = XOR(x[13],ROTATE(PLUS(x[12],x[15]), 9));
    x[14] = XOR(x[14],ROTATE(PLUS(x[13],x[12]),13));
    x[15] = XOR(x[15],ROTATE(PLUS(x[14],x[13]),18));
  }
  for (i = 0;i < 16;++i) x[i] = PLUS(x[i],input[i]);
  for (i = 0;i < 16;++i) U32TO8_LITTLE(output + 4 * i,x[i]);
}

static const char sigma[16] = "expand 32-byte k";
static const char tau[16] = "expand 16-byte k";

void
salsa20_set_key(struct salsa20_ctx *ctx,
		unsigned length, const uint8_t *key)
{
  const char *constants;

  assert (length == SALSA20_MIN_KEY_SIZE || length == SALSA20_MAX_KEY_SIZE);

  ctx->input[1] = U8TO32_LITTLE(key + 0);
  ctx->input[2] = U8TO32_LITTLE(key + 4);
  ctx->input[3] = U8TO32_LITTLE(key + 8);
  ctx->input[4] = U8TO32_LITTLE(key + 12);
  if (length == SALSA20_MAX_KEY_SIZE) { /* recommended */
    key += 16;
    constants = sigma;
  } else { /* kbits == 128 */
    constants = tau;
  }
  ctx->input[11] = U8TO32_LITTLE(key + 0);
  ctx->input[12] = U8TO32_LITTLE(key + 4);
  ctx->input[13] = U8TO32_LITTLE(key + 8);
  ctx->input[14] = U8TO32_LITTLE(key + 12);
  ctx->input[0] = U8TO32_LITTLE(constants + 0);
  ctx->input[5] = U8TO32_LITTLE(constants + 4);
  ctx->input[10] = U8TO32_LITTLE(constants + 8);
  ctx->input[15] = U8TO32_LITTLE(constants + 12);
}

void
salsa20_set_iv(struct salsa20_ctx *ctx, unsigned length, const uint8_t *iv)
{
  assert (length == SALSA20_IV_SIZE);

  ctx->input[6] = U8TO32_LITTLE(iv + 0);
  ctx->input[7] = U8TO32_LITTLE(iv + 4);
  ctx->input[8] = 0;
  ctx->input[9] = 0;
}

void
salsa20_crypt(struct salsa20_ctx *ctx,
	      unsigned length,
	      uint8_t *c,
	      const uint8_t *m)
{
  uint8_t output[64];
  unsigned i;

  if (!length) return;
  for (;;) {
    salsa20_wordtobyte(output,ctx->input);
    ctx->input[8] = PLUSONE(ctx->input[8]);
    if (!ctx->input[8]) {
      ctx->input[9] = PLUSONE(ctx->input[9]);
      /* stopping at 2^70 length per nonce is user's responsibility */
    }
    if (length <= 64) {
      for (i = 0;i < length;++i) c[i] = m[i] ^ output[i];
      return;
    }
    for (i = 0;i < 64;++i) c[i] = m[i] ^ output[i];
    length -= 64;
    c += 64;
    m += 64;
  }
}