_ Git - BearSSL/blob - src/rsa/rsa_i32_pub.c

   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 }