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/*
* Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "inner.h"
/* see inner.h */
uint32_t
br_rsa_pss_sig_pad(const br_prng_class **rng,
const br_hash_class *hf_data, const br_hash_class *hf_mgf1,
const unsigned char *hash, size_t salt_len,
uint32_t n_bitlen, unsigned char *x)
{
size_t xlen, hash_len;
br_hash_compat_context hc;
unsigned char *salt, *seed;
hash_len = br_digest_size(hf_data);
/*
* The padded string is one bit smaller than the modulus;
* notably, if the modulus length is equal to 1 modulo 8, then
* the padded string will be one _byte_ smaller, and the first
* byte will be set to 0. We apply these transformations here.
*/
n_bitlen --;
if ((n_bitlen & 7) == 0) {
*x ++ = 0;
}
xlen = (n_bitlen + 7) >> 3;
/*
* Check that the modulus is large enough for the hash value
* length combined with the intended salt length.
*/
if (hash_len > xlen || salt_len > xlen
|| (hash_len + salt_len + 2) > xlen)
{
return 0;
}
/*
* Produce a random salt.
*/
salt = x + xlen - hash_len - salt_len - 1;
if (salt_len != 0) {
(*rng)->generate(rng, salt, salt_len);
}
/*
* Compute the seed for MGF1.
*/
seed = x + xlen - hash_len - 1;
hf_data->init(&hc.vtable);
memset(seed, 0, 8);
hf_data->update(&hc.vtable, seed, 8);
hf_data->update(&hc.vtable, hash, hash_len);
hf_data->update(&hc.vtable, salt, salt_len);
hf_data->out(&hc.vtable, seed);
/*
* Prepare string PS (padded salt). The salt is already at the
* right place.
*/
memset(x, 0, xlen - salt_len - hash_len - 2);
x[xlen - salt_len - hash_len - 2] = 0x01;
/*
* Generate the mask and XOR it into PS.
*/
br_mgf1_xor(x, xlen - hash_len - 1, hf_mgf1, seed, hash_len);
/*
* Clear the top bits to ensure the value is lower than the
* modulus.
*/
x[0] &= 0xFF >> (((uint32_t)xlen << 3) - n_bitlen);
/*
* The seed (H) is already in the right place. We just set the
* last byte.
*/
x[xlen - 1] = 0xBC;
return 1;
}
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