1*0957b409SSimon J. Gerraty /* 2*0957b409SSimon J. Gerraty * Copyright (c) 2018 Thomas Pornin <pornin@bolet.org> 3*0957b409SSimon J. Gerraty * 4*0957b409SSimon J. Gerraty * Permission is hereby granted, free of charge, to any person obtaining 5*0957b409SSimon J. Gerraty * a copy of this software and associated documentation files (the 6*0957b409SSimon J. Gerraty * "Software"), to deal in the Software without restriction, including 7*0957b409SSimon J. Gerraty * without limitation the rights to use, copy, modify, merge, publish, 8*0957b409SSimon J. Gerraty * distribute, sublicense, and/or sell copies of the Software, and to 9*0957b409SSimon J. Gerraty * permit persons to whom the Software is furnished to do so, subject to 10*0957b409SSimon J. Gerraty * the following conditions: 11*0957b409SSimon J. Gerraty * 12*0957b409SSimon J. Gerraty * The above copyright notice and this permission notice shall be 13*0957b409SSimon J. Gerraty * included in all copies or substantial portions of the Software. 14*0957b409SSimon J. Gerraty * 15*0957b409SSimon J. Gerraty * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 16*0957b409SSimon J. Gerraty * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 17*0957b409SSimon J. Gerraty * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 18*0957b409SSimon J. Gerraty * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS 19*0957b409SSimon J. Gerraty * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN 20*0957b409SSimon J. Gerraty * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN 21*0957b409SSimon J. Gerraty * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 22*0957b409SSimon J. Gerraty * SOFTWARE. 23*0957b409SSimon J. Gerraty */ 24*0957b409SSimon J. Gerraty 25*0957b409SSimon J. Gerraty #include "inner.h" 26*0957b409SSimon J. Gerraty 27*0957b409SSimon J. Gerraty /* see inner.h */ 28*0957b409SSimon J. Gerraty uint32_t 29*0957b409SSimon J. Gerraty br_rsa_pss_sig_pad(const br_prng_class **rng, 30*0957b409SSimon J. Gerraty const br_hash_class *hf_data, const br_hash_class *hf_mgf1, 31*0957b409SSimon J. Gerraty const unsigned char *hash, size_t salt_len, 32*0957b409SSimon J. Gerraty uint32_t n_bitlen, unsigned char *x) 33*0957b409SSimon J. Gerraty { 34*0957b409SSimon J. Gerraty size_t xlen, hash_len; 35*0957b409SSimon J. Gerraty br_hash_compat_context hc; 36*0957b409SSimon J. Gerraty unsigned char *salt, *seed; 37*0957b409SSimon J. Gerraty 38*0957b409SSimon J. Gerraty hash_len = br_digest_size(hf_data); 39*0957b409SSimon J. Gerraty 40*0957b409SSimon J. Gerraty /* 41*0957b409SSimon J. Gerraty * The padded string is one bit smaller than the modulus; 42*0957b409SSimon J. Gerraty * notably, if the modulus length is equal to 1 modulo 8, then 43*0957b409SSimon J. Gerraty * the padded string will be one _byte_ smaller, and the first 44*0957b409SSimon J. Gerraty * byte will be set to 0. We apply these transformations here. 45*0957b409SSimon J. Gerraty */ 46*0957b409SSimon J. Gerraty n_bitlen --; 47*0957b409SSimon J. Gerraty if ((n_bitlen & 7) == 0) { 48*0957b409SSimon J. Gerraty *x ++ = 0; 49*0957b409SSimon J. Gerraty } 50*0957b409SSimon J. Gerraty xlen = (n_bitlen + 7) >> 3; 51*0957b409SSimon J. Gerraty 52*0957b409SSimon J. Gerraty /* 53*0957b409SSimon J. Gerraty * Check that the modulus is large enough for the hash value 54*0957b409SSimon J. Gerraty * length combined with the intended salt length. 55*0957b409SSimon J. Gerraty */ 56*0957b409SSimon J. Gerraty if (hash_len > xlen || salt_len > xlen 57*0957b409SSimon J. Gerraty || (hash_len + salt_len + 2) > xlen) 58*0957b409SSimon J. Gerraty { 59*0957b409SSimon J. Gerraty return 0; 60*0957b409SSimon J. Gerraty } 61*0957b409SSimon J. Gerraty 62*0957b409SSimon J. Gerraty /* 63*0957b409SSimon J. Gerraty * Produce a random salt. 64*0957b409SSimon J. Gerraty */ 65*0957b409SSimon J. Gerraty salt = x + xlen - hash_len - salt_len - 1; 66*0957b409SSimon J. Gerraty if (salt_len != 0) { 67*0957b409SSimon J. Gerraty (*rng)->generate(rng, salt, salt_len); 68*0957b409SSimon J. Gerraty } 69*0957b409SSimon J. Gerraty 70*0957b409SSimon J. Gerraty /* 71*0957b409SSimon J. Gerraty * Compute the seed for MGF1. 72*0957b409SSimon J. Gerraty */ 73*0957b409SSimon J. Gerraty seed = x + xlen - hash_len - 1; 74*0957b409SSimon J. Gerraty hf_data->init(&hc.vtable); 75*0957b409SSimon J. Gerraty memset(seed, 0, 8); 76*0957b409SSimon J. Gerraty hf_data->update(&hc.vtable, seed, 8); 77*0957b409SSimon J. Gerraty hf_data->update(&hc.vtable, hash, hash_len); 78*0957b409SSimon J. Gerraty hf_data->update(&hc.vtable, salt, salt_len); 79*0957b409SSimon J. Gerraty hf_data->out(&hc.vtable, seed); 80*0957b409SSimon J. Gerraty 81*0957b409SSimon J. Gerraty /* 82*0957b409SSimon J. Gerraty * Prepare string PS (padded salt). The salt is already at the 83*0957b409SSimon J. Gerraty * right place. 84*0957b409SSimon J. Gerraty */ 85*0957b409SSimon J. Gerraty memset(x, 0, xlen - salt_len - hash_len - 2); 86*0957b409SSimon J. Gerraty x[xlen - salt_len - hash_len - 2] = 0x01; 87*0957b409SSimon J. Gerraty 88*0957b409SSimon J. Gerraty /* 89*0957b409SSimon J. Gerraty * Generate the mask and XOR it into PS. 90*0957b409SSimon J. Gerraty */ 91*0957b409SSimon J. Gerraty br_mgf1_xor(x, xlen - hash_len - 1, hf_mgf1, seed, hash_len); 92*0957b409SSimon J. Gerraty 93*0957b409SSimon J. Gerraty /* 94*0957b409SSimon J. Gerraty * Clear the top bits to ensure the value is lower than the 95*0957b409SSimon J. Gerraty * modulus. 96*0957b409SSimon J. Gerraty */ 97*0957b409SSimon J. Gerraty x[0] &= 0xFF >> (((uint32_t)xlen << 3) - n_bitlen); 98*0957b409SSimon J. Gerraty 99*0957b409SSimon J. Gerraty /* 100*0957b409SSimon J. Gerraty * The seed (H) is already in the right place. We just set the 101*0957b409SSimon J. Gerraty * last byte. 102*0957b409SSimon J. Gerraty */ 103*0957b409SSimon J. Gerraty x[xlen - 1] = 0xBC; 104*0957b409SSimon J. Gerraty 105*0957b409SSimon J. Gerraty return 1; 106*0957b409SSimon J. Gerraty } 107