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/*
* ChaCha cipher.
*
* Copyright (c) 2014 Marko Kreen
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* Based on: chacha-ref.c version 20080118 / D. J. Bernstein / Public domain.
*/
#include <usual/crypto/chacha.h>
#include <usual/endian.h>
#include <usual/bits.h>
#define CHACHA_ROUNDS 20
#define QUARTERROUND(in, out, a, b, c, d) \
do { \
out[a] = in[a] + in[b]; out[d] = rol32(in[d] ^ out[a], 16); \
out[c] = in[c] + out[d]; out[b] = rol32(in[b] ^ out[c], 12); \
out[a] = out[a] + out[b]; out[d] = rol32(out[d] ^ out[a], 8); \
out[c] = out[c] + out[d]; out[b] = rol32(out[b] ^ out[c], 7); \
} while (0)
#define OUTPUT(a,b,c,d) \
do { \
output[a] = htole32(x[a] + input[a]); \
output[b] = htole32(x[b] + input[b]); \
output[c] = htole32(x[c] + input[c]); \
output[d] = htole32(x[d] + input[d]); \
} while (0)
/* mix full state. needs 2 call sites to avoid inlining */
static void chacha_mix(struct ChaCha *ctx)
{
const uint32_t *input = ctx->state;
uint32_t *output = ctx->u.output32;
int i;
uint32_t x[16];
/* first "column" round */
QUARTERROUND(input, x, 0, 4, 8, 12);
QUARTERROUND(input, x, 1, 5, 9, 13);
QUARTERROUND(input, x, 2, 6, 10, 14);
QUARTERROUND(input, x, 3, 7, 11, 15);
for (i = 0; i < CHACHA_ROUNDS/2 - 1; i++) {
/* "diagonal" round */
QUARTERROUND(x, x, 0, 5, 10, 15);
QUARTERROUND(x, x, 1, 6, 11, 12);
QUARTERROUND(x, x, 2, 7, 8, 13);
QUARTERROUND(x, x, 3, 4, 9, 14);
/* "column" round */
QUARTERROUND(x, x, 0, 4, 8, 12);
QUARTERROUND(x, x, 1, 5, 9, 13);
QUARTERROUND(x, x, 2, 6, 10, 14);
QUARTERROUND(x, x, 3, 7, 11, 15);
}
/* last "diagonal" round */
QUARTERROUND(x, x, 0, 5, 10, 15); OUTPUT(0, 5, 10, 15);
QUARTERROUND(x, x, 1, 6, 11, 12); OUTPUT(1, 6, 11, 12);
QUARTERROUND(x, x, 2, 7, 8, 13); OUTPUT(2, 7, 8, 13);
QUARTERROUND(x, x, 3, 4, 9, 14); OUTPUT(3, 4, 9, 14);
ctx->pos = 0;
ctx->state[12]++;
if (!ctx->state[12])
ctx->state[13]++;
}
void chacha_set_key_256(struct ChaCha *ctx, const void *key)
{
unsigned int i;
memcpy(&ctx->state[0], "expand 32-byte k", 16);
memcpy(&ctx->state[4], key, 32);
for (i = 0; i < 12; i++)
ctx->state[i] = le32toh(ctx->state[i]);
ctx->pos = CHACHA_BLOCK_SIZE;
}
void chacha_set_key_128(struct ChaCha *ctx, const void *key)
{
unsigned int i;
memcpy(&ctx->state[0], "expand 16-byte k", 16);
memcpy(&ctx->state[4], key, 16);
memcpy(&ctx->state[8], key, 16);
for (i = 0; i < 12; i++)
ctx->state[i] = le32toh(ctx->state[i]);
ctx->pos = CHACHA_BLOCK_SIZE;
}
void chacha_set_nonce(struct ChaCha *ctx, uint32_t counter_low, uint32_t counter_high, const void *iv)
{
const uint8_t *_iv = iv;
ctx->state[12] = counter_low;
ctx->state[13] = counter_high;
if (_iv) {
ctx->state[14] = le32dec(_iv);
ctx->state[15] = le32dec(_iv + 4);
}
ctx->pos = CHACHA_BLOCK_SIZE;
}
void chacha_keystream(struct ChaCha *ctx, void *stream, size_t bytes)
{
unsigned int n, avail;
const uint8_t *ks = ctx->u.output8;
uint8_t *dst = stream;
while (bytes > 0) {
if (ctx->pos >= CHACHA_BLOCK_SIZE)
chacha_mix(ctx);
avail = CHACHA_BLOCK_SIZE - ctx->pos;
n = (bytes > avail) ? avail : bytes;
memcpy(dst, ks + ctx->pos, n);
bytes -= n;
dst += n;
ctx->pos += n;
}
}
void chacha_keystream_xor(struct ChaCha *ctx, const void *plain, void *encrypted, size_t bytes)
{
unsigned int i, n, avail;
const uint8_t *ks = ctx->u.output8;
const uint8_t *src = plain;
uint8_t *dst = encrypted;
while (bytes > 0) {
if (ctx->pos >= CHACHA_BLOCK_SIZE)
chacha_mix(ctx);
avail = CHACHA_BLOCK_SIZE - ctx->pos;
n = (bytes > avail) ? avail : bytes;
for (i = 0; i < n; i++)
dst[i] = src[i] ^ ks[i];
bytes -= n;
dst += n;
src += n;
ctx->pos += n;
}
}
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