3a11226e49446667136e5825d9a171649f01aced
[BearSSL] / src / ec / ecdsa_atr.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_ec.h */
28 size_t
29 br_ecdsa_asn1_to_raw(void *sig, size_t sig_len)
30 {
31 /*
32 * Note: this code is a bit lenient in that it accepts a few
33 * deviations to DER with regards to minimality of encoding of
34 * lengths and integer values. These deviations are still
35 * unambiguous.
36 *
37 * Signature format is a SEQUENCE of two INTEGER values. We
38 * support only integers of less than 127 bytes each (signed
39 * encoding) so the resulting raw signature will have length
40 * at most 254 bytes.
41 */
42
43 unsigned char *buf, *r, *s;
44 size_t zlen, rlen, slen, off;
45 unsigned char tmp[254];
46
47 buf = sig;
48 if (sig_len < 8) {
49 return 0;
50 }
51
52 /*
53 * First byte is SEQUENCE tag.
54 */
55 if (buf[0] != 0x30) {
56 return 0;
57 }
58
59 /*
60 * The SEQUENCE length will be encoded over one or two bytes. We
61 * limit the total SEQUENCE contents to 255 bytes, because it
62 * makes things simpler; this is enough for subgroup orders up
63 * to 999 bits.
64 */
65 zlen = buf[1];
66 if (zlen > 0x80) {
67 if (zlen != 0x81) {
68 return 0;
69 }
70 zlen = buf[2];
71 if (zlen != sig_len - 3) {
72 return 0;
73 }
74 off = 3;
75 } else {
76 if (zlen != sig_len - 2) {
77 return 0;
78 }
79 off = 2;
80 }
81
82 /*
83 * First INTEGER (r).
84 */
85 if (buf[off ++] != 0x02) {
86 return 0;
87 }
88 rlen = buf[off ++];
89 if (rlen >= 0x80) {
90 return 0;
91 }
92 r = buf + off;
93 off += rlen;
94
95 /*
96 * Second INTEGER (s).
97 */
98 if (off + 2 > sig_len) {
99 return 0;
100 }
101 if (buf[off ++] != 0x02) {
102 return 0;
103 }
104 slen = buf[off ++];
105 if (slen >= 0x80 || slen != sig_len - off) {
106 return 0;
107 }
108 s = buf + off;
109
110 /*
111 * Removing leading zeros from r and s.
112 */
113 while (rlen > 0 && *r == 0) {
114 rlen --;
115 r ++;
116 }
117 while (slen > 0 && *s == 0) {
118 slen --;
119 s ++;
120 }
121
122 /*
123 * Compute common length for the two integers, then copy integers
124 * into the temporary buffer, and finally copy it back over the
125 * signature buffer.
126 */
127 zlen = rlen > slen ? rlen : slen;
128 sig_len = zlen << 1;
129 memset(tmp, 0, sig_len);
130 memcpy(tmp + zlen - rlen, r, rlen);
131 memcpy(tmp + sig_len - slen, s, slen);
132 memcpy(sig, tmp, sig_len);
133 return sig_len;
134 }