1 /* 2 * Copyright (c) 2016 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 bearssl_rsa.h */ 28 uint32_t 29 br_rsa_i32_public(unsigned char *x, size_t xlen, 30 const br_rsa_public_key *pk) 31 { 32 const unsigned char *n; 33 size_t nlen; 34 uint32_t m[1 + (BR_MAX_RSA_SIZE >> 5)]; 35 uint32_t a[1 + (BR_MAX_RSA_SIZE >> 5)]; 36 uint32_t t1[1 + (BR_MAX_RSA_SIZE >> 5)]; 37 uint32_t t2[1 + (BR_MAX_RSA_SIZE >> 5)]; 38 uint32_t m0i, r; 39 40 /* 41 * Get the actual length of the modulus, and see if it fits within 42 * our stack buffer. We also check that the length of x[] is valid. 43 */ 44 n = pk->n; 45 nlen = pk->nlen; 46 while (nlen > 0 && *n == 0) { 47 n ++; 48 nlen --; 49 } 50 if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) { 51 return 0; 52 } 53 br_i32_decode(m, n, nlen); 54 m0i = br_i32_ninv32(m[1]); 55 56 /* 57 * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be 58 * an odd integer. 59 */ 60 r = m0i & 1; 61 62 /* 63 * Decode x[] into a[]; we also check that its value is proper. 64 */ 65 r &= br_i32_decode_mod(a, x, xlen, m); 66 67 /* 68 * Compute the modular exponentiation. 69 */ 70 br_i32_modpow(a, pk->e, pk->elen, m, m0i, t1, t2); 71 72 /* 73 * Encode the result. 74 */ 75 br_i32_encode(x, xlen, a); 76 return r; 77 } 78