_ Git - BearSSL/blob - src/ec/ecdsa_rta.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 static size_t
  28 asn1_int_length(const unsigned char *x, size_t xlen)
  29 {
  30         while (xlen > 0 && *x == 0) {
  31                 x ++;
  32                 xlen --;
  33         }
  34         if (xlen == 0 || *x >= 0x80) {
  35                 xlen ++;
  36         }
  37         return xlen;
  38 }
  39
  40 /* see bearssl_ec.h */
  41 size_t
  42 br_ecdsa_raw_to_asn1(void *sig, size_t sig_len)
  43 {
  44         /*
  45          * Internal buffer is large enough to accommodate a signature
  46          * such that r and s fit on 125 bytes each (signed encoding),
  47          * meaning a curve order of up to 1000 bits. This is the limit
  48          * that ensures "simple" length encodings.
  49          */
  50         unsigned char *buf;
  51         size_t hlen, rlen, slen, zlen, off;
  52         unsigned char tmp[257];
  53
  54         buf = sig;
  55         if ((sig_len & 1) != 0) {
  56                 return 0;
  57         }
  58         hlen = sig_len >> 1;
  59         rlen = asn1_int_length(buf, hlen);
  60         slen = asn1_int_length(buf + hlen, hlen);
  61         if (rlen > 125 || slen > 125) {
  62                 return 0;
  63         }
  64         tmp[0] = 0x30;
  65         zlen = rlen + slen + 4;
  66         if (zlen >= 0x80) {
  67                 tmp[1] = 0x81;
  68                 tmp[2] = zlen;
  69                 off = 3;
  70         } else {
  71                 tmp[1] = zlen;
  72                 off = 2;
  73         }
  74         tmp[off ++] = 0x02;
  75         tmp[off ++] = rlen;
  76         if (rlen > hlen) {
  77                 tmp[off] = 0x00;
  78                 memcpy(tmp + off + 1, buf, hlen);
  79         } else {
  80                 memcpy(tmp + off, buf + hlen - rlen, rlen);
  81         }
  82         off += rlen;
  83         tmp[off ++] = 0x02;
  84         tmp[off ++] = slen;
  85         if (slen > hlen) {
  86                 tmp[off] = 0x00;
  87                 memcpy(tmp + off + 1, buf + hlen, hlen);
  88         } else {
  89                 memcpy(tmp + off, buf + sig_len - slen, slen);
  90         }
  91         off += slen;
  92         memcpy(sig, tmp, off);
  93         return off;
  94 }