_ Git - BearSSL/blob - src/rsa/rsa_i62_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 #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