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cryb-to/lib/cipher/cryb_salsa.c
Dag-Erling Smørgrav b28507b0e9 Fix counter increment in Salsa and ChaCha.
In my eagerness to eliminate a branch which is taken once per 2^38 bytes of keystream, I forgot that the state words are in host order.  Thus, the counter increment code worked fine on little-endian machines, but not on big-endian ones.  Switch to a simpler (branchful) solution.
2017-04-22 03:10:10 +02:00

202 lines
5.8 KiB
C

/*-
* Copyright (c) 2017 Dag-Erling Smørgrav
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include "cryb/impl.h"
#include <stdint.h>
#include <string.h>
#include <cryb/assert.h>
#include <cryb/bitwise.h>
#include <cryb/endian.h>
#include <cryb/memset_s.h>
#include <cryb/salsa.h>
#define SALSA_QR(x, a, b, c, d) \
do { \
x[a] ^= rol32(x[d] + x[c], 7); \
x[b] ^= rol32(x[a] + x[d], 9); \
x[c] ^= rol32(x[b] + x[a], 13); \
x[d] ^= rol32(x[c] + x[b], 18); \
} while (0)
static const char magic128[] = "expand 16-byte k";
static const char magic256[] = "expand 32-byte k";
/*
* Fill the state array with 16 bytes of magic and 32 bytes of key,
* repeating the key if necessary. The 8-byte stream position and the
* 8-byte nonce are initialized to all-zeroes. The number of rounds is
* set to 20, the most commonly used value.
*/
void
salsa_init(salsa_ctx *ctx, cipher_mode mode CRYB_UNUSED,
const uint8_t *key, size_t keylen)
{
assert(mode == CIPHER_MODE_ENCRYPT || mode == CIPHER_MODE_DECRYPT);
assert(keylen == 16 || keylen == 32);
memset(ctx, 0, sizeof *ctx);
if (keylen == 32) {
/* magic */
ctx->state[ 0] = le32dec(magic256 + 0);
ctx->state[ 5] = le32dec(magic256 + 4);
ctx->state[10] = le32dec(magic256 + 8);
ctx->state[15] = le32dec(magic256 + 12);
/* first half of key */
ctx->state[ 1] = le32dec(key + 0);
ctx->state[ 2] = le32dec(key + 4);
ctx->state[ 3] = le32dec(key + 8);
ctx->state[ 4] = le32dec(key + 12);
/* second half of key */
ctx->state[11] = le32dec(key + 16);
ctx->state[12] = le32dec(key + 20);
ctx->state[13] = le32dec(key + 24);
ctx->state[14] = le32dec(key + 28);
} else {
/* magic */
ctx->state[ 0] = le32dec(magic128 + 0);
ctx->state[ 5] = le32dec(magic128 + 4);
ctx->state[10] = le32dec(magic128 + 8);
ctx->state[15] = le32dec(magic128 + 12);
/* first half of key */
ctx->state[ 1] = le32dec(key + 0);
ctx->state[ 2] = le32dec(key + 4);
ctx->state[ 3] = le32dec(key + 8);
ctx->state[ 4] = le32dec(key + 12);
/* repeat first half of key */
ctx->state[11] = le32dec(key + 0);
ctx->state[12] = le32dec(key + 4);
ctx->state[13] = le32dec(key + 8);
ctx->state[14] = le32dec(key + 12);
}
ctx->rounds = 20;
}
/*
* Reset the stream position, load a new nonce, and change the number of
* rounds if requested.
*/
void
salsa_reset(salsa_ctx *ctx, const uint8_t *nonce, unsigned int rounds)
{
/* reset stream counter */
ctx->state[8] = 0;
ctx->state[9] = 0;
/* copy nonce */
ctx->state[6] = le32dec(nonce + 0);
ctx->state[7] = le32dec(nonce + 4);
/* set rounds if specified */
if (rounds != 0)
ctx->rounds = rounds;
}
/*
* Generate a block of keystream.
*/
size_t
salsa_keystream(salsa_ctx *ctx, uint8_t *ks, size_t len)
{
return (salsa_encrypt(ctx, NULL, ks, len));
}
/*
* Encryption: generate a block of keystream, xor it with the plaintext to
* produce the ciphertext, and increment the stream position.
*/
size_t
salsa_encrypt(salsa_ctx *ctx, const void *vpt, uint8_t *ct, size_t len)
{
const uint8_t *pt = vpt;
uint32_t mix[16];
uint8_t ks[64];
unsigned int b, i;
len -= len % sizeof ks;
for (b = 0; b < len; b += sizeof ks) {
memcpy(mix, ctx->state, sizeof mix);
for (i = 0; i < ctx->rounds; i += 2) {
SALSA_QR(mix, 4, 8, 12, 0);
SALSA_QR(mix, 9, 13, 1, 5);
SALSA_QR(mix, 14, 2, 6, 10);
SALSA_QR(mix, 3, 7, 11, 15);
SALSA_QR(mix, 1, 2, 3, 0);
SALSA_QR(mix, 6, 7, 4, 5);
SALSA_QR(mix, 11, 8, 9, 10);
SALSA_QR(mix, 12, 13, 14, 15);
}
for (i = 0; i < 16; ++i)
le32enc(ks + i * 4, ctx->state[i] + mix[i]);
if (pt == NULL) {
memcpy(ct, ks, sizeof ks);
ct += sizeof ks;
} else {
for (i = 0; i < 64 && i < len; ++i)
*ct++ = *pt++ ^ ks[i];
}
if (++ctx->state[12] == 0)
++ctx->state[13];
}
return (len);
}
/*
* Decryption: identical to encryption.
*/
size_t
salsa_decrypt(salsa_ctx *ctx, const uint8_t *ct, void *vpt, size_t len)
{
return (salsa_encrypt(ctx, ct, vpt, len));
}
/*
* Wipe our state.
*/
void
salsa_finish(salsa_ctx *ctx)
{
(void)memset_s(ctx, 0, sizeof *ctx, sizeof *ctx);
}
cipher_algorithm salsa_cipher = {
.name = "salsa",
.contextlen = sizeof(salsa_ctx),
.blocklen = 64,
.keylen = 32,
.init = (cipher_init_func)salsa_init,
.keystream = (cipher_keystream_func)salsa_keystream,
.encrypt = (cipher_encrypt_func)salsa_encrypt,
.decrypt = (cipher_decrypt_func)salsa_decrypt,
.finish = (cipher_finish_func)salsa_finish,
};