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 #if BR_INT128 || BR_UMUL128 28 29 /* 30 * As a strict minimum, we need four buffers that can hold a 31 * modular integer. But TLEN is expressed in 64-bit words. 32 */ 33 #define TLEN (2 * (2 + ((BR_MAX_RSA_SIZE + 30) / 31))) 34 35 /* see bearssl_rsa.h */ 36 uint32_t 37 br_rsa_i62_public(unsigned char *x, size_t xlen, 38 const br_rsa_public_key *pk) 39 { 40 const unsigned char *n; 41 size_t nlen; 42 uint64_t tmp[TLEN]; 43 uint32_t *m, *a; 44 size_t fwlen; 45 long z; 46 uint32_t m0i, r; 47 48 /* 49 * Get the actual length of the modulus, and see if it fits within 50 * our stack buffer. We also check that the length of x[] is valid. 51 */ 52 n = pk->n; 53 nlen = pk->nlen; 54 while (nlen > 0 && *n == 0) { 55 n ++; 56 nlen --; 57 } 58 if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) { 59 return 0; 60 } 61 z = (long)nlen << 3; 62 fwlen = 1; 63 while (z > 0) { 64 z -= 31; 65 fwlen ++; 66 } 67 /* 68 * Convert fwlen to a count in 62-bit words. 69 */ 70 fwlen = (fwlen + 1) >> 1; 71 72 /* 73 * The modulus gets decoded into m[]. 74 * The value to exponentiate goes into a[]. 75 */ 76 m = (uint32_t *)tmp; 77 a = (uint32_t *)(tmp + fwlen); 78 79 /* 80 * Decode the modulus. 81 */ 82 br_i31_decode(m, n, nlen); 83 m0i = br_i31_ninv31(m[1]); 84 85 /* 86 * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be 87 * an odd integer. 88 */ 89 r = m0i & 1; 90 91 /* 92 * Decode x[] into a[]; we also check that its value is proper. 93 */ 94 r &= br_i31_decode_mod(a, x, xlen, m); 95 96 /* 97 * Compute the modular exponentiation. 98 */ 99 br_i62_modpow_opt(a, pk->e, pk->elen, m, m0i, 100 tmp + 2 * fwlen, TLEN - 2 * fwlen); 101 102 /* 103 * Encode the result. 104 */ 105 br_i31_encode(x, xlen, a); 106 return r; 107 } 108 109 /* see bearssl_rsa.h */ 110 br_rsa_public 111 br_rsa_i62_public_get(void) 112 { 113 return &br_rsa_i62_public; 114 } 115 116 #else 117 118 /* see bearssl_rsa.h */ 119 br_rsa_public 120 br_rsa_i62_public_get(void) 121 { 122 return 0; 123 } 124 125 #endif 126