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 */
34static size_t
35asn1_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 */
48size_t
49br_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}
122