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 /* 28 * Hash some data. This is put as a separate function so that stack 29 * allocation of the hash function context is done only for the duration 30 * of the hash. 31 */ 32 static void 33 hash_data(const br_hash_class *dig, void *dst, const void *src, size_t len) 34 { 35 br_hash_compat_context hc; 36 37 hc.vtable = dig; 38 dig->init(&hc.vtable); 39 dig->update(&hc.vtable, src, len); 40 dig->out(&hc.vtable, dst); 41 } 42 43 /* see inner.h */ 44 size_t 45 br_rsa_oaep_pad(const br_prng_class **rnd, const br_hash_class *dig, 46 const void *label, size_t label_len, 47 const br_rsa_public_key *pk, 48 void *dst, size_t dst_max_len, 49 const void *src, size_t src_len) 50 { 51 size_t k, hlen; 52 unsigned char *buf; 53 54 hlen = br_digest_size(dig); 55 56 /* 57 * Compute actual modulus length (in bytes). 58 */ 59 k = pk->nlen; 60 while (k > 0 && pk->n[k - 1] == 0) { 61 k --; 62 } 63 64 /* 65 * An error is reported if: 66 * - the modulus is too short; 67 * - the source message length is too long; 68 * - the destination buffer is too short. 69 */ 70 if (k < ((hlen << 1) + 2) 71 || src_len > (k - (hlen << 1) - 2) 72 || dst_max_len < k) 73 { 74 return 0; 75 } 76 77 /* 78 * Apply padding. At this point, things cannot fail. 79 */ 80 buf = dst; 81 82 /* 83 * Assemble: DB = lHash || PS || 0x01 || M 84 * We first place the source message M with memmove(), so that 85 * overlaps between source and destination buffers are supported. 86 */ 87 memmove(buf + k - src_len, src, src_len); 88 hash_data(dig, buf + 1 + hlen, label, label_len); 89 memset(buf + 1 + (hlen << 1), 0, k - src_len - (hlen << 1) - 2); 90 buf[k - src_len - 1] = 0x01; 91 92 /* 93 * Make the random seed. 94 */ 95 (*rnd)->generate(rnd, buf + 1, hlen); 96 97 /* 98 * Mask DB with the mask generated from the seed. 99 */ 100 br_mgf1_xor(buf + 1 + hlen, k - hlen - 1, dig, buf + 1, hlen); 101 102 /* 103 * Mask the seed with the mask generated from the masked DB. 104 */ 105 br_mgf1_xor(buf + 1, hlen, dig, buf + 1 + hlen, k - hlen - 1); 106 107 /* 108 * Padding result: EM = 0x00 || maskedSeed || maskedDB. 109 */ 110 buf[0] = 0x00; 111 return k; 112 } 113