1*0957b409SSimon J. Gerraty /* 2*0957b409SSimon J. Gerraty * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org> 3*0957b409SSimon J. Gerraty * 4*0957b409SSimon J. Gerraty * Permission is hereby granted, free of charge, to any person obtaining 5*0957b409SSimon J. Gerraty * a copy of this software and associated documentation files (the 6*0957b409SSimon J. Gerraty * "Software"), to deal in the Software without restriction, including 7*0957b409SSimon J. Gerraty * without limitation the rights to use, copy, modify, merge, publish, 8*0957b409SSimon J. Gerraty * distribute, sublicense, and/or sell copies of the Software, and to 9*0957b409SSimon J. Gerraty * permit persons to whom the Software is furnished to do so, subject to 10*0957b409SSimon J. Gerraty * the following conditions: 11*0957b409SSimon J. Gerraty * 12*0957b409SSimon J. Gerraty * The above copyright notice and this permission notice shall be 13*0957b409SSimon J. Gerraty * included in all copies or substantial portions of the Software. 14*0957b409SSimon J. Gerraty * 15*0957b409SSimon J. Gerraty * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 16*0957b409SSimon J. Gerraty * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 17*0957b409SSimon J. Gerraty * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 18*0957b409SSimon J. Gerraty * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS 19*0957b409SSimon J. Gerraty * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN 20*0957b409SSimon J. Gerraty * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN 21*0957b409SSimon J. Gerraty * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 22*0957b409SSimon J. Gerraty * SOFTWARE. 23*0957b409SSimon J. Gerraty */ 24*0957b409SSimon J. Gerraty 25*0957b409SSimon J. Gerraty #include "inner.h" 26*0957b409SSimon J. Gerraty 27*0957b409SSimon J. Gerraty /* 28*0957b409SSimon J. Gerraty * As a strict minimum, we need four buffers that can hold a 29*0957b409SSimon J. Gerraty * modular integer. 30*0957b409SSimon J. Gerraty */ 31*0957b409SSimon J. Gerraty #define TLEN (4 * (2 + ((BR_MAX_RSA_SIZE + 14) / 15))) 32*0957b409SSimon J. Gerraty 33*0957b409SSimon J. Gerraty /* see bearssl_rsa.h */ 34*0957b409SSimon J. Gerraty uint32_t 35*0957b409SSimon J. Gerraty br_rsa_i15_public(unsigned char *x, size_t xlen, 36*0957b409SSimon J. Gerraty const br_rsa_public_key *pk) 37*0957b409SSimon J. Gerraty { 38*0957b409SSimon J. Gerraty const unsigned char *n; 39*0957b409SSimon J. Gerraty size_t nlen; 40*0957b409SSimon J. Gerraty uint16_t tmp[1 + TLEN]; 41*0957b409SSimon J. Gerraty uint16_t *m, *a, *t; 42*0957b409SSimon J. Gerraty size_t fwlen; 43*0957b409SSimon J. Gerraty long z; 44*0957b409SSimon J. Gerraty uint16_t m0i; 45*0957b409SSimon J. Gerraty uint32_t r; 46*0957b409SSimon J. Gerraty 47*0957b409SSimon J. Gerraty /* 48*0957b409SSimon J. Gerraty * Get the actual length of the modulus, and see if it fits within 49*0957b409SSimon J. Gerraty * our stack buffer. We also check that the length of x[] is valid. 50*0957b409SSimon J. Gerraty */ 51*0957b409SSimon J. Gerraty n = pk->n; 52*0957b409SSimon J. Gerraty nlen = pk->nlen; 53*0957b409SSimon J. Gerraty while (nlen > 0 && *n == 0) { 54*0957b409SSimon J. Gerraty n ++; 55*0957b409SSimon J. Gerraty nlen --; 56*0957b409SSimon J. Gerraty } 57*0957b409SSimon J. Gerraty if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) { 58*0957b409SSimon J. Gerraty return 0; 59*0957b409SSimon J. Gerraty } 60*0957b409SSimon J. Gerraty z = (long)nlen << 3; 61*0957b409SSimon J. Gerraty fwlen = 1; 62*0957b409SSimon J. Gerraty while (z > 0) { 63*0957b409SSimon J. Gerraty z -= 15; 64*0957b409SSimon J. Gerraty fwlen ++; 65*0957b409SSimon J. Gerraty } 66*0957b409SSimon J. Gerraty /* 67*0957b409SSimon J. Gerraty * Round up length to an even number. 68*0957b409SSimon J. Gerraty */ 69*0957b409SSimon J. Gerraty fwlen += (fwlen & 1); 70*0957b409SSimon J. Gerraty 71*0957b409SSimon J. Gerraty /* 72*0957b409SSimon J. Gerraty * The modulus gets decoded into m[]. 73*0957b409SSimon J. Gerraty * The value to exponentiate goes into a[]. 74*0957b409SSimon J. Gerraty * The temporaries for modular exponentiations are in t[]. 75*0957b409SSimon J. Gerraty * 76*0957b409SSimon J. Gerraty * We want the first value word of each integer to be aligned 77*0957b409SSimon J. Gerraty * on a 32-bit boundary. 78*0957b409SSimon J. Gerraty */ 79*0957b409SSimon J. Gerraty m = tmp; 80*0957b409SSimon J. Gerraty if (((uintptr_t)m & 2) == 0) { 81*0957b409SSimon J. Gerraty m ++; 82*0957b409SSimon J. Gerraty } 83*0957b409SSimon J. Gerraty a = m + fwlen; 84*0957b409SSimon J. Gerraty t = m + 2 * fwlen; 85*0957b409SSimon J. Gerraty 86*0957b409SSimon J. Gerraty /* 87*0957b409SSimon J. Gerraty * Decode the modulus. 88*0957b409SSimon J. Gerraty */ 89*0957b409SSimon J. Gerraty br_i15_decode(m, n, nlen); 90*0957b409SSimon J. Gerraty m0i = br_i15_ninv15(m[1]); 91*0957b409SSimon J. Gerraty 92*0957b409SSimon J. Gerraty /* 93*0957b409SSimon J. Gerraty * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be 94*0957b409SSimon J. Gerraty * an odd integer. 95*0957b409SSimon J. Gerraty */ 96*0957b409SSimon J. Gerraty r = m0i & 1; 97*0957b409SSimon J. Gerraty 98*0957b409SSimon J. Gerraty /* 99*0957b409SSimon J. Gerraty * Decode x[] into a[]; we also check that its value is proper. 100*0957b409SSimon J. Gerraty */ 101*0957b409SSimon J. Gerraty r &= br_i15_decode_mod(a, x, xlen, m); 102*0957b409SSimon J. Gerraty 103*0957b409SSimon J. Gerraty /* 104*0957b409SSimon J. Gerraty * Compute the modular exponentiation. 105*0957b409SSimon J. Gerraty */ 106*0957b409SSimon J. Gerraty br_i15_modpow_opt(a, pk->e, pk->elen, m, m0i, t, TLEN - 2 * fwlen); 107*0957b409SSimon J. Gerraty 108*0957b409SSimon J. Gerraty /* 109*0957b409SSimon J. Gerraty * Encode the result. 110*0957b409SSimon J. Gerraty */ 111*0957b409SSimon J. Gerraty br_i15_encode(x, xlen, a); 112*0957b409SSimon J. Gerraty return r; 113*0957b409SSimon J. Gerraty } 114