New basic implementation of Curve25519 (generic i15 code, experimental).
[BearSSL] / 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 }