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 bearssl_rsa.h */ 28 size_t 29 br_rsa_i31_compute_modulus(void *n, const br_rsa_private_key *sk) 30 { 31 uint32_t tmp[2 * ((BR_MAX_RSA_SIZE + 30) / 31) + 5]; 32 uint32_t *t, *p, *q; 33 const unsigned char *pbuf, *qbuf; 34 size_t nlen, plen, qlen, tlen; 35 36 /* 37 * Compute actual byte and lengths for p and q. 38 */ 39 pbuf = sk->p; 40 plen = sk->plen; 41 while (plen > 0 && *pbuf == 0) { 42 pbuf ++; 43 plen --; 44 } 45 qbuf = sk->q; 46 qlen = sk->qlen; 47 while (qlen > 0 && *qbuf == 0) { 48 qbuf ++; 49 qlen --; 50 } 51 52 t = tmp; 53 tlen = (sizeof tmp) / (sizeof tmp[0]); 54 55 /* 56 * Decode p. 57 */ 58 if ((31 * tlen) < (plen << 3) + 31) { 59 return 0; 60 } 61 br_i31_decode(t, pbuf, plen); 62 p = t; 63 plen = (p[0] + 63) >> 5; 64 t += plen; 65 tlen -= plen; 66 67 /* 68 * Decode q. 69 */ 70 if ((31 * tlen) < (qlen << 3) + 31) { 71 return 0; 72 } 73 br_i31_decode(t, qbuf, qlen); 74 q = t; 75 qlen = (q[0] + 63) >> 5; 76 t += qlen; 77 tlen -= qlen; 78 79 /* 80 * Computation can proceed only if we have enough room for the 81 * modulus. 82 */ 83 if (tlen < (plen + qlen + 1)) { 84 return 0; 85 } 86 87 /* 88 * Private key already contains the modulus bit length, from which 89 * we can infer the output length. Even if n is NULL, we still had 90 * to decode p and q to make sure that the product can be computed. 91 */ 92 nlen = (sk->n_bitlen + 7) >> 3; 93 if (n != NULL) { 94 br_i31_zero(t, p[0]); 95 br_i31_mulacc(t, p, q); 96 br_i31_encode(n, nlen, t); 97 } 98 return nlen; 99 } 100