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/*
* cifra - embedded cryptography library
* Written in 2014 by Joseph Birr-Pixton <jpixton@gmail.com>
*
* To the extent possible under law, the author(s) have dedicated all
* copyright and related and neighboring rights to this software to the
* public domain worldwide. This software is distributed without any
* warranty.
*
* You should have received a copy of the CC0 Public Domain Dedication
* along with this software. If not, see
* <http://creativecommons.org/publicdomain/zero/1.0/>.
*/
#include "bitops.h"
#include "salsa20.h"
#include "blockwise.h"
#include "tassert.h"
#include <string.h>
#include <stdlib.h>
void cf_chacha20_core(const uint8_t key0[16],
const uint8_t key1[16],
const uint8_t nonce[16],
const uint8_t constant[16],
uint8_t out[64])
{
uint32_t z0, z1, z2, z3, z4, z5, z6, z7,
z8, z9, za, zb, zc, zd, ze, zf;
uint32_t x0 = z0 = read32_le(constant + 0),
x1 = z1 = read32_le(constant + 4),
x2 = z2 = read32_le(constant + 8),
x3 = z3 = read32_le(constant + 12),
x4 = z4 = read32_le(key0 + 0),
x5 = z5 = read32_le(key0 + 4),
x6 = z6 = read32_le(key0 + 8),
x7 = z7 = read32_le(key0 + 12),
x8 = z8 = read32_le(key1 + 0),
x9 = z9 = read32_le(key1 + 4),
xa = za = read32_le(key1 + 8),
xb = zb = read32_le(key1 + 12),
xc = zc = read32_le(nonce + 0),
xd = zd = read32_le(nonce + 4),
xe = ze = read32_le(nonce + 8),
xf = zf = read32_le(nonce + 12);
#define QUARTER(a, b, c, d) \
a += b; d = rotl32(d ^ a, 16); \
c += d; b = rotl32(b ^ c, 12); \
a += b; d = rotl32(d ^ a, 8); \
c += d; b = rotl32(b ^ c, 7);
int i;
for (i = 0; i < 10; i++)
{
QUARTER(z0, z4, z8, zc);
QUARTER(z1, z5, z9, zd);
QUARTER(z2, z6, za, ze);
QUARTER(z3, z7, zb, zf);
QUARTER(z0, z5, za, zf);
QUARTER(z1, z6, zb, zc);
QUARTER(z2, z7, z8, zd);
QUARTER(z3, z4, z9, ze);
}
x0 += z0;
x1 += z1;
x2 += z2;
x3 += z3;
x4 += z4;
x5 += z5;
x6 += z6;
x7 += z7;
x8 += z8;
x9 += z9;
xa += za;
xb += zb;
xc += zc;
xd += zd;
xe += ze;
xf += zf;
write32_le(x0, out + 0);
write32_le(x1, out + 4);
write32_le(x2, out + 8);
write32_le(x3, out + 12);
write32_le(x4, out + 16);
write32_le(x5, out + 20);
write32_le(x6, out + 24);
write32_le(x7, out + 28);
write32_le(x8, out + 32);
write32_le(x9, out + 36);
write32_le(xa, out + 40);
write32_le(xb, out + 44);
write32_le(xc, out + 48);
write32_le(xd, out + 52);
write32_le(xe, out + 56);
write32_le(xf, out + 60);
}
static const uint8_t *chacha20_tau = (const uint8_t *) "expand 16-byte k";
static const uint8_t *chacha20_sigma = (const uint8_t *) "expand 32-byte k";
static void set_key(cf_chacha20_ctx *ctx, const uint8_t *key, size_t nkey)
{
switch (nkey)
{
case 16:
memcpy(ctx->key0, key, 16);
memcpy(ctx->key1, key, 16);
ctx->constant = chacha20_tau;
break;
case 32:
memcpy(ctx->key0, key, 16);
memcpy(ctx->key1, key + 16, 16);
ctx->constant = chacha20_sigma;
break;
default:
abort();
}
}
void cf_chacha20_init(cf_chacha20_ctx *ctx, const uint8_t *key, size_t nkey, const uint8_t nonce[8])
{
set_key(ctx, key, nkey);
memset(ctx->nonce, 0, sizeof ctx->nonce);
memcpy(ctx->nonce + 8, nonce, 8);
ctx->nblock = 0;
ctx->ncounter = 8;
}
void cf_chacha20_init_custom(cf_chacha20_ctx *ctx, const uint8_t *key, size_t nkey,
const uint8_t nonce[16], size_t ncounter)
{
assert(ncounter > 0);
set_key(ctx, key, nkey);
memcpy(ctx->nonce, nonce, sizeof ctx->nonce);
ctx->nblock = 0;
ctx->ncounter = ncounter;
}
static void cf_chacha20_next_block(void *vctx, uint8_t *out)
{
cf_chacha20_ctx *ctx = vctx;
cf_chacha20_core(ctx->key0,
ctx->key1,
ctx->nonce,
ctx->constant,
out);
incr_le(ctx->nonce, ctx->ncounter);
}
void cf_chacha20_cipher(cf_chacha20_ctx *ctx, const uint8_t *input, uint8_t *output, size_t bytes)
{
cf_blockwise_xor(ctx->block, &ctx->nblock, 64,
input, output, bytes,
cf_chacha20_next_block,
ctx);
}
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