1 /* 2 * Copyright (c) 2018 Thomas Pornin <pornin@bolet.org> 3 * 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: 11 * 12 * The above copyright notice and this permission notice shall be 13 * included in all copies or substantial portions of the Software. 14 * 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 22 * SOFTWARE. 23 */ 24 25 #include "inner.h" 26 27 /* see inner.h */ 28 uint32_t 29 br_rsa_pss_sig_unpad(const br_hash_class *hf_data, 30 const br_hash_class *hf_mgf1, 31 const unsigned char *hash, size_t salt_len, 32 const br_rsa_public_key *pk, unsigned char *x) 33 { 34 size_t u, xlen, hash_len; 35 br_hash_compat_context hc; 36 unsigned char *seed, *salt; 37 unsigned char tmp[64]; 38 uint32_t r, n_bitlen; 39 40 hash_len = br_digest_size(hf_data); 41 42 /* 43 * Value r will be set to a non-zero value is any test fails. 44 */ 45 r = 0; 46 47 /* 48 * The value bit length (as an integer) must be strictly less than 49 * that of the modulus. 50 */ 51 for (u = 0; u < pk->nlen; u ++) { 52 if (pk->n[u] != 0) { 53 break; 54 } 55 } 56 if (u == pk->nlen) { 57 return 0; 58 } 59 n_bitlen = BIT_LENGTH(pk->n[u]) + ((uint32_t)(pk->nlen - u - 1) << 3); 60 n_bitlen --; 61 if ((n_bitlen & 7) == 0) { 62 r |= *x ++; 63 } else { 64 r |= x[0] & (0xFF << (n_bitlen & 7)); 65 } 66 xlen = (n_bitlen + 7) >> 3; 67 68 /* 69 * Check that the modulus is large enough for the hash value 70 * length combined with the intended salt length. 71 */ 72 if (hash_len > xlen || salt_len > xlen 73 || (hash_len + salt_len + 2) > xlen) 74 { 75 return 0; 76 } 77 78 /* 79 * Check value of rightmost byte. 80 */ 81 r |= x[xlen - 1] ^ 0xBC; 82 83 /* 84 * Generate the mask and XOR it into the first bytes to reveal PS; 85 * we must also mask out the leading bits. 86 */ 87 seed = x + xlen - hash_len - 1; 88 br_mgf1_xor(x, xlen - hash_len - 1, hf_mgf1, seed, hash_len); 89 if ((n_bitlen & 7) != 0) { 90 x[0] &= 0xFF >> (8 - (n_bitlen & 7)); 91 } 92 93 /* 94 * Check that all padding bytes have the expected value. 95 */ 96 for (u = 0; u < (xlen - hash_len - salt_len - 2); u ++) { 97 r |= x[u]; 98 } 99 r |= x[xlen - hash_len - salt_len - 2] ^ 0x01; 100 101 /* 102 * Recompute H. 103 */ 104 salt = x + xlen - hash_len - salt_len - 1; 105 hf_data->init(&hc.vtable); 106 memset(tmp, 0, 8); 107 hf_data->update(&hc.vtable, tmp, 8); 108 hf_data->update(&hc.vtable, hash, hash_len); 109 hf_data->update(&hc.vtable, salt, salt_len); 110 hf_data->out(&hc.vtable, tmp); 111 112 /* 113 * Check that the recomputed H value matches the one appearing 114 * in the string. 115 */ 116 for (u = 0; u < hash_len; u ++) { 117 r |= tmp[u] ^ x[(xlen - salt_len - 1) + u]; 118 } 119 120 return EQ0(r); 121 } 122