2 * Copyright (c) 2018 Thomas Pornin <pornin@bolet.org>
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
6 * "Software"), to deal in the Software without restriction, including
7 * without limitation the rights to use, copy, modify, merge, publish,
8 * distribute, sublicense, and/or sell copies of the Software, and to
9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
29 br_rsa_pss_sig_pad(const br_prng_class
**rng
,
30 const br_hash_class
*hf_data
, const br_hash_class
*hf_mgf1
,
31 const unsigned char *hash
, size_t salt_len
,
32 uint32_t n_bitlen
, unsigned char *x
)
34 size_t xlen
, hash_len
;
35 br_hash_compat_context hc
;
36 unsigned char *salt
, *seed
;
38 hash_len
= br_digest_size(hf_data
);
41 * The padded string is one bit smaller than the modulus;
42 * notably, if the modulus length is equal to 1 modulo 8, then
43 * the padded string will be one _byte_ smaller, and the first
44 * byte will be set to 0. We apply these transformations here.
47 if ((n_bitlen
& 7) == 0) {
50 xlen
= (n_bitlen
+ 7) >> 3;
53 * Check that the modulus is large enough for the hash value
54 * length combined with the intended salt length.
56 if (hash_len
> xlen
|| salt_len
> xlen
57 || (hash_len
+ salt_len
+ 2) > xlen
)
63 * Produce a random salt.
65 salt
= x
+ xlen
- hash_len
- salt_len
- 1;
67 (*rng
)->generate(rng
, salt
, salt_len
);
71 * Compute the seed for MGF1.
73 seed
= x
+ xlen
- hash_len
- 1;
74 hf_data
->init(&hc
.vtable
);
76 hf_data
->update(&hc
.vtable
, seed
, 8);
77 hf_data
->update(&hc
.vtable
, hash
, hash_len
);
78 hf_data
->update(&hc
.vtable
, salt
, salt_len
);
79 hf_data
->out(&hc
.vtable
, seed
);
82 * Prepare string PS (padded salt). The salt is already at the
85 memset(x
, 0, xlen
- salt_len
- hash_len
- 2);
86 x
[xlen
- salt_len
- hash_len
- 2] = 0x01;
89 * Generate the mask and XOR it into PS.
91 br_mgf1_xor(x
, xlen
- hash_len
- 1, hf_mgf1
, seed
, hash_len
);
94 * Clear the top bits to ensure the value is lower than the
97 x
[0] &= 0xFF >> (((uint32_t)xlen
<< 3) - n_bitlen
);
100 * The seed (H) is already in the right place. We just set the