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/*
* Copyright (C) 2020 Olivier Chéron <olivier.cheron@gmail.com>
*
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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 <cryptonite_hash_prefix.h>
void CRYPTONITE_HASHED(finalize_prefix)(struct HASHED_LOWER(ctx) *ctx, const uint8_t *data, uint32_t len, uint32_t n, uint8_t *out)
{
uint64_t bits[HASHED(BITS_ELEMS)];
uint8_t *p = (uint8_t *) &bits;
uint32_t index, padidx, padlen, pos, out_mask;
static const uint32_t cut_off = HASHED(BLOCK_SIZE) - sizeof(bits);
/* Make sure n <= len */
n += (len - n) & constant_time_lt(len, n);
/* Initial index, based on current context state */
index = CRYPTONITE_HASHED(get_index)(ctx);
/* Final size after n bytes */
CRYPTONITE_HASHED(incr_sz)(ctx, bits, n);
/* Padding index and length */
padidx = CRYPTONITE_HASHED(get_index)(ctx);
padlen = HASHED(BLOCK_SIZE) + cut_off - padidx;
padlen -= HASHED(BLOCK_SIZE) & constant_time_lt(padidx, cut_off);
/* Initialize buffers because we will XOR into them */
memset(ctx->buf + index, 0, HASHED(BLOCK_SIZE) - index);
memset(out, 0, HASHED(DIGEST_SIZE));
pos = 0;
/* Iterate based on the full buffer length, regardless of n, and include
* the maximum overhead with padding and size bytes
*/
while (pos < len + HASHED(BLOCK_SIZE) + sizeof(bits)) {
uint8_t b;
/* Take as many bytes from the input buffer as possible */
if (pos < len)
b = *(data++) & (uint8_t) constant_time_lt(pos, n);
else
b = 0;
/* First padding byte */
b |= 0x80 & (uint8_t) constant_time_eq(pos, n);
/* Size bytes are always at the end of a block */
if (index >= cut_off)
b |= p[index - cut_off] & (uint8_t) constant_time_ge(pos, n + padlen);
/* Store this byte into the buffer */
ctx->buf[index++] ^= b;
pos++;
/* Process a full block, at a boundary which is independent from n */
if (index >= HASHED(BLOCK_SIZE)) {
index = 0;
HASHED_LOWER(do_chunk)(ctx, (void *) ctx->buf);
memset(ctx->buf, 0, HASHED(BLOCK_SIZE));
/* Try to store the result: this is a no-op except when we reach the
* actual size based on n, more iterations may continue after that
* when len is really larger
*/
out_mask = constant_time_eq(pos, n + padlen + sizeof(bits));
CRYPTONITE_HASHED(select_digest)(ctx, out, out_mask);
}
}
}
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