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 #define U (1 + (BR_MAX_RSA_FACTOR >> 5)) 28 29 /* see bearssl_rsa.h */ 30 uint32_t 31 br_rsa_i32_private(unsigned char *x, const br_rsa_private_key *sk) 32 { 33 const unsigned char *p, *q; 34 size_t plen, qlen; 35 uint32_t tmp[6 * U]; 36 uint32_t *mp, *mq, *s1, *s2, *t1, *t2, *t3; 37 uint32_t p0i, q0i; 38 size_t xlen, u; 39 uint32_t r; 40 41 /* 42 * All our temporary buffers are from the tmp[] array. 43 * 44 * The mp, mq, s1, s2, t1 and t2 buffers are large enough to 45 * contain a RSA factor. The t3 buffer can contain a complete 46 * RSA modulus. t3 shares its storage space with s2, s1 and t1, 47 * in that order (this is important, see below). 48 */ 49 mq = tmp; 50 mp = tmp + U; 51 t2 = tmp + 2 * U; 52 s2 = tmp + 3 * U; 53 s1 = tmp + 4 * U; 54 t1 = tmp + 5 * U; 55 t3 = s2; 56 57 /* 58 * Compute the actual lengths (in bytes) of p and q, and check 59 * that they fit within our stack buffers. 60 */ 61 p = sk->p; 62 plen = sk->plen; 63 while (plen > 0 && *p == 0) { 64 p ++; 65 plen --; 66 } 67 q = sk->q; 68 qlen = sk->qlen; 69 while (qlen > 0 && *q == 0) { 70 q ++; 71 qlen --; 72 } 73 if (plen > (BR_MAX_RSA_FACTOR >> 3) 74 || qlen > (BR_MAX_RSA_FACTOR >> 3)) 75 { 76 return 0; 77 } 78 79 /* 80 * Decode p and q. 81 */ 82 br_i32_decode(mp, p, plen); 83 br_i32_decode(mq, q, qlen); 84 85 /* 86 * Recompute modulus, to compare with the source value. 87 */ 88 br_i32_zero(t2, mp[0]); 89 br_i32_mulacc(t2, mp, mq); 90 xlen = (sk->n_bitlen + 7) >> 3; 91 br_i32_encode(t2 + 2 * U, xlen, t2); 92 u = xlen; 93 r = 0; 94 while (u > 0) { 95 uint32_t wn, wx; 96 97 u --; 98 wn = ((unsigned char *)(t2 + 2 * U))[u]; 99 wx = x[u]; 100 r = ((wx - (wn + r)) >> 8) & 1; 101 } 102 103 /* 104 * Compute s1 = x^dp mod p. 105 */ 106 p0i = br_i32_ninv32(mp[1]); 107 br_i32_decode_reduce(s1, x, xlen, mp); 108 br_i32_modpow(s1, sk->dp, sk->dplen, mp, p0i, t1, t2); 109 110 /* 111 * Compute s2 = x^dq mod q. 112 */ 113 q0i = br_i32_ninv32(mq[1]); 114 br_i32_decode_reduce(s2, x, xlen, mq); 115 br_i32_modpow(s2, sk->dq, sk->dqlen, mq, q0i, t1, t2); 116 117 /* 118 * Compute: 119 * h = (s1 - s2)*(1/q) mod p 120 * s1 is an integer modulo p, but s2 is modulo q. PKCS#1 is 121 * unclear about whether p may be lower than q (some existing, 122 * widely deployed implementations of RSA don't tolerate p < q), 123 * but we want to support that occurrence, so we need to use the 124 * reduction function. 125 * 126 * Since we use br_i32_decode_reduce() for iq (purportedly, the 127 * inverse of q modulo p), we also tolerate improperly large 128 * values for this parameter. 129 */ 130 br_i32_reduce(t2, s2, mp); 131 br_i32_add(s1, mp, br_i32_sub(s1, t2, 1)); 132 br_i32_to_monty(s1, mp); 133 br_i32_decode_reduce(t1, sk->iq, sk->iqlen, mp); 134 br_i32_montymul(t2, s1, t1, mp, p0i); 135 136 /* 137 * h is now in t2. We compute the final result: 138 * s = s2 + q*h 139 * All these operations are non-modular. 140 * 141 * We need mq, s2 and t2. We use the t3 buffer as destination. 142 * The buffers mp, s1 and t1 are no longer needed. Moreover, 143 * the first step is to copy s2 into the destination buffer t3. 144 * We thus arranged for t3 to actually share space with s2, and 145 * to be followed by the space formerly used by s1 and t1. 146 */ 147 br_i32_mulacc(t3, mq, t2); 148 149 /* 150 * Encode the result. Since we already checked the value of xlen, 151 * we can just use it right away. 152 */ 153 br_i32_encode(x, xlen, t3); 154 155 /* 156 * The only error conditions remaining at that point are invalid 157 * values for p and q (even integers). 158 */ 159 return p0i & q0i & r; 160 } 161