_ 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 /*
  28  * Compute ASN.1 encoded length for the provided integer. The ASN.1
  29  * encoding is signed, so its leading bit must have value 0; it must
  30  * also be of minimal length (so leading bytes of value 0 must be
  31  * removed, except if that would contradict the rule about the sign
  32  * bit).
  33  */
  34 static size_t
  35 asn1_int_length(const unsigned char *x, size_t xlen)
  36 {
  37         while (xlen > 0 && *x == 0) {
  38                 x ++;
  39                 xlen --;
  40         }
  41         if (xlen == 0 || *x >= 0x80) {
  42                 xlen ++;
  43         }
  44         return xlen;
  45 }
  46
  47 /* see bearssl_ec.h */
  48 size_t
  49 br_ecdsa_raw_to_asn1(void *sig, size_t sig_len)
  50 {
  51         /*
  52          * Internal buffer is large enough to accommodate a signature
  53          * such that r and s fit on 125 bytes each (signed encoding),
  54          * meaning a curve order of up to 999 bits. This is the limit
  55          * that ensures "simple" length encodings.
  56          */
  57         unsigned char *buf;
  58         size_t hlen, rlen, slen, zlen, off;
  59         unsigned char tmp[257];
  60
  61         buf = sig;
  62         if ((sig_len & 1) != 0) {
  63                 return 0;
  64         }
  65
  66         /*
  67          * Compute lengths for the two integers.
  68          */
  69         hlen = sig_len >> 1;
  70         rlen = asn1_int_length(buf, hlen);
  71         slen = asn1_int_length(buf + hlen, hlen);
  72         if (rlen > 125 || slen > 125) {
  73                 return 0;
  74         }
  75
  76         /*
  77          * SEQUENCE header.
  78          */
  79         tmp[0] = 0x30;
  80         zlen = rlen + slen + 4;
  81         if (zlen >= 0x80) {
  82                 tmp[1] = 0x81;
  83                 tmp[2] = zlen;
  84                 off = 3;
  85         } else {
  86                 tmp[1] = zlen;
  87                 off = 2;
  88         }
  89
  90         /*
  91          * First INTEGER (r).
  92          */
  93         tmp[off ++] = 0x02;
  94         tmp[off ++] = rlen;
  95         if (rlen > hlen) {
  96                 tmp[off] = 0x00;
  97                 memcpy(tmp + off + 1, buf, hlen);
  98         } else {
  99                 memcpy(tmp + off, buf + hlen - rlen, rlen);
 100         }
 101         off += rlen;
 102
 103         /*
 104          * Second INTEGER (s).
 105          */
 106         tmp[off ++] = 0x02;
 107         tmp[off ++] = slen;
 108         if (slen > hlen) {
 109                 tmp[off] = 0x00;
 110                 memcpy(tmp + off + 1, buf + hlen, hlen);
 111         } else {
 112                 memcpy(tmp + off, buf + sig_len - slen, slen);
 113         }
 114         off += slen;
 115
 116         /*
 117          * Return ASN.1 signature.
 118          */
 119         memcpy(sig, tmp, off);
 120         return off;
 121 }