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/*
* Copyright (c) 2016 Brandon Hamilton <brandon.hamilton@gmail.com>
*
* 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. Neither the name of the author nor the names of his contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 AUTHORS 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 <stdint.h>
#include <string.h>
#include "cryptonite_xsalsa.h"
#include "cryptonite_align.h"
#include "cryptonite_bitfn.h"
/* XSalsa20 algorithm as described in https://cr.yp.to/snuffle/xsalsa-20081128.pdf */
void cryptonite_xsalsa_init(cryptonite_salsa_context *ctx, uint8_t nb_rounds,
uint32_t keylen, const uint8_t *key,
uint32_t ivlen, const uint8_t *iv)
{
memset(ctx, 0, sizeof(*ctx));
ctx->nb_rounds = nb_rounds;
/* Create initial 512-bit input block:
(x0, x5, x10, x15) is the Salsa20 constant
(x1, x2, x3, x4, x11, x12, x13, x14) is a 256-bit key
(x6, x7, x8, x9) is the first 128 bits of a 192-bit nonce
*/
cryptonite_salsa_init_core(&ctx->st, keylen, key, 8, iv);
/* Continue initialization in a separate function that may also
be called independently */
cryptonite_xsalsa_derive(ctx, ivlen - 8, iv + 8);
}
void cryptonite_xsalsa_derive(cryptonite_salsa_context *ctx,
uint32_t ivlen, const uint8_t *iv)
{
/* Finish creating initial 512-bit input block:
(x6, x7, x8, x9) is the first 128 bits of a 192-bit nonce
Except iv has been shifted by 64 bits so there are now only 128 bits ahead.
*/
ctx->st.d[ 8] += load_le32(iv + 0);
ctx->st.d[ 9] += load_le32(iv + 4);
/* Compute (z0, z1, . . . , z15) = doubleround ^(r/2) (x0, x1, . . . , x15) */
block hSalsa;
memset(&hSalsa, 0, sizeof(block));
cryptonite_salsa_core_xor(ctx->nb_rounds, &hSalsa, &ctx->st);
/* Build a new 512-bit input block (x′0, x′1, . . . , x′15):
(x′0, x′5, x′10, x′15) is the Salsa20 constant
(x′1,x′2,x′3,x′4,x′11,x′12,x′13,x′14) = (z0,z5,z10,z15,z6,z7,z8,z9)
(x′6,x′7) is the last 64 bits of the 192-bit nonce
(x′8, x′9) is a 64-bit block counter.
*/
ctx->st.d[ 1] = hSalsa.d[ 0] - ctx->st.d[ 0];
ctx->st.d[ 2] = hSalsa.d[ 5] - ctx->st.d[ 5];
ctx->st.d[ 3] = hSalsa.d[10] - ctx->st.d[10];
ctx->st.d[ 4] = hSalsa.d[15] - ctx->st.d[15];
ctx->st.d[11] = hSalsa.d[ 6] - ctx->st.d[ 6];
ctx->st.d[12] = hSalsa.d[ 7] - ctx->st.d[ 7];
ctx->st.d[13] = hSalsa.d[ 8] - ctx->st.d[ 8];
ctx->st.d[14] = hSalsa.d[ 9] - ctx->st.d[ 9];
ctx->st.d[ 6] = load_le32(iv + 8);
ctx->st.d[ 7] = load_le32(iv + 12);
ctx->st.d[ 8] = 0;
ctx->st.d[ 9] = 0;
}
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