_ Git - BearSSL/blob - src/rsa/rsa_i32_pkcs1_sign.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_pkcs1_sign(const unsigned char *hash_oid,
  30         const unsigned char *hash, size_t hash_len,
  31         const br_rsa_private_key *sk, unsigned char *x)
  32 {
  33         size_t u, x3, xlen;
  34
  35         /*
  36          * Padded hash value has format:
  37          *  00 01 FF .. FF 00 30 x1 30 x2 06 x3 OID 05 00 04 x4 HASH
  38          *
  39          * with the following rules:
  40          *
  41          *  -- Total length is equal to the modulus length (unsigned
  42          *     encoding).
  43          *
  44          *  -- There must be at least eight bytes of value 0xFF.
  45          *
  46          *  -- x4 is equal to the hash length (hash_len).
  47          *
  48          *  -- x3 is equal to the encoded OID value length (hash_oid[0]).
  49          *
  50          *  -- x2 = x3 + 4.
  51          *
  52          *  -- x1 = x2 + x4 + 4 = x3 + x4 + 8.
  53          *
  54          * Note: the "05 00" is optional (signatures with and without
  55          * that sequence exist in practice), but notes in PKCS#1 seem to
  56          * indicate that the presence of that sequence (specifically,
  57          * an ASN.1 NULL value for the hash parameters) may be slightly
  58          * more "standard" than the opposite.
  59          */
  60         xlen = (sk->n_bitlen + 7) >> 3;
  61
  62         if (hash_oid == NULL) {
  63                 if (xlen < hash_len + 11) {
  64                         return 0;
  65                 }
  66                 x[0] = 0x00;
  67                 x[1] = 0x01;
  68                 u = xlen - hash_len;
  69                 memset(x + 2, 0xFF, u - 3);
  70                 x[u - 1] = 0x00;
  71         } else {
  72                 x3 = hash_oid[0];
  73
  74                 /*
  75                  * Check that there is enough room for all the elements,
  76                  * including at least eight bytes of value 0xFF.
  77                  */
  78                 if (xlen < (x3 + hash_len + 21)) {
  79                         return 0;
  80                 }
  81                 x[0] = 0x00;
  82                 x[1] = 0x01;
  83                 u = xlen - x3 - hash_len - 11;
  84                 memset(x + 2, 0xFF, u - 2);
  85                 x[u] = 0x00;
  86                 x[u + 1] = 0x30;
  87                 x[u + 2] = x3 + hash_len + 8;
  88                 x[u + 3] = 0x30;
  89                 x[u + 4] = x3 + 4;
  90                 x[u + 5] = 0x06;
  91                 memcpy(x + u + 6, hash_oid, x3 + 1);
  92                 u += x3 + 7;
  93                 x[u ++] = 0x05;
  94                 x[u ++] = 0x00;
  95                 x[u ++] = 0x04;
  96                 x[u ++] = hash_len;
  97         }
  98         memcpy(x + u, hash, hash_len);
  99
 100         /*
 101          * Do the actual computation.
 102          */
 103         return br_rsa_i32_private(x, sk);
 104 }