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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_unpad(const br_hash_class *hf_data,
const br_hash_class *hf_mgf1,
const unsigned char *hash, size_t salt_len,
const br_rsa_public_key *pk, unsigned char *x)
{
size_t u, xlen, hash_len;
br_hash_compat_context hc;
unsigned char *seed, *salt;
unsigned char tmp[64];
uint32_t r, n_bitlen;
hash_len = br_digest_size(hf_data);
/*
* Value r will be set to a non-zero value is any test fails.
*/
r = 0;
/*
* The value bit length (as an integer) must be strictly less than
* that of the modulus.
*/
for (u = 0; u < pk->nlen; u ++) {
if (pk->n[u] != 0) {
break;
}
}
if (u == pk->nlen) {
return 0;
}
n_bitlen = BIT_LENGTH(pk->n[u]) + ((uint32_t)(pk->nlen - u - 1) << 3);
n_bitlen --;
if ((n_bitlen & 7) == 0) {
r |= *x ++;
} else {
r |= x[0] & (0xFF << (n_bitlen & 7));
}
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;
}
/*
* Check value of rightmost byte.
*/
r |= x[xlen - 1] ^ 0xBC;
/*
* Generate the mask and XOR it into the first bytes to reveal PS;
* we must also mask out the leading bits.
*/
seed = x + xlen - hash_len - 1;
br_mgf1_xor(x, xlen - hash_len - 1, hf_mgf1, seed, hash_len);
if ((n_bitlen & 7) != 0) {
x[0] &= 0xFF >> (8 - (n_bitlen & 7));
}
/*
* Check that all padding bytes have the expected value.
*/
for (u = 0; u < (xlen - hash_len - salt_len - 2); u ++) {
r |= x[u];
}
r |= x[xlen - hash_len - salt_len - 2] ^ 0x01;
/*
* Recompute H.
*/
salt = x + xlen - hash_len - salt_len - 1;
hf_data->init(&hc.vtable);
memset(tmp, 0, 8);
hf_data->update(&hc.vtable, tmp, 8);
hf_data->update(&hc.vtable, hash, hash_len);
hf_data->update(&hc.vtable, salt, salt_len);
hf_data->out(&hc.vtable, tmp);
/*
* Check that the recomputed H value matches the one appearing
* in the string.
*/
for (u = 0; u < hash_len; u ++) {
r |= tmp[u] ^ x[(xlen - salt_len - 1) + u];
}
return EQ0(r);
}
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