asn1.c revision 8d520ff1dc2da35cdca849e982051b86468016d8 
1/*
2 * ASN.1 DER parsing
3 * Copyright (c) 2006, Jouni Malinen <j@w1.fi>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8 *
9 * Alternatively, this software may be distributed under the terms of BSD
10 * license.
11 *
12 * See README and COPYING for more details.
13 */
14
15#include "includes.h"
16
17#include "common.h"
18#include "asn1.h"
19
20int asn1_get_next(const u8 *buf, size_t len, struct asn1_hdr *hdr)
21{
22	const u8 *pos, *end;
23	u8 tmp;
24
25	os_memset(hdr, 0, sizeof(*hdr));
26	pos = buf;
27	end = buf + len;
28
29	hdr->identifier = *pos++;
30	hdr->class = hdr->identifier >> 6;
31	hdr->constructed = !!(hdr->identifier & (1 << 5));
32
33	if ((hdr->identifier & 0x1f) == 0x1f) {
34		hdr->tag = 0;
35		do {
36			if (pos >= end) {
37				wpa_printf(MSG_DEBUG, "ASN.1: Identifier "
38					   "underflow");
39				return -1;
40			}
41			tmp = *pos++;
42			wpa_printf(MSG_MSGDUMP, "ASN.1: Extended tag data: "
43				   "0x%02x", tmp);
44			hdr->tag = (hdr->tag << 7) | (tmp & 0x7f);
45		} while (tmp & 0x80);
46	} else
47		hdr->tag = hdr->identifier & 0x1f;
48
49	tmp = *pos++;
50	if (tmp & 0x80) {
51		if (tmp == 0xff) {
52			wpa_printf(MSG_DEBUG, "ASN.1: Reserved length "
53				   "value 0xff used");
54			return -1;
55		}
56		tmp &= 0x7f; /* number of subsequent octets */
57		hdr->length = 0;
58		if (tmp > 4) {
59			wpa_printf(MSG_DEBUG, "ASN.1: Too long length field");
60			return -1;
61		}
62		while (tmp--) {
63			if (pos >= end) {
64				wpa_printf(MSG_DEBUG, "ASN.1: Length "
65					   "underflow");
66				return -1;
67			}
68			hdr->length = (hdr->length << 8) | *pos++;
69		}
70	} else {
71		/* Short form - length 0..127 in one octet */
72		hdr->length = tmp;
73	}
74
75	if (end < pos || hdr->length > (unsigned int) (end - pos)) {
76		wpa_printf(MSG_DEBUG, "ASN.1: Contents underflow");
77		return -1;
78	}
79
80	hdr->payload = pos;
81	return 0;
82}
83
84
85int asn1_parse_oid(const u8 *buf, size_t len, struct asn1_oid *oid)
86{
87	const u8 *pos, *end;
88	unsigned long val;
89	u8 tmp;
90
91	os_memset(oid, 0, sizeof(*oid));
92
93	pos = buf;
94	end = buf + len;
95
96	while (pos < end) {
97		val = 0;
98
99		do {
100			if (pos >= end)
101				return -1;
102			tmp = *pos++;
103			val = (val << 7) | (tmp & 0x7f);
104		} while (tmp & 0x80);
105
106		if (oid->len >= ASN1_MAX_OID_LEN) {
107			wpa_printf(MSG_DEBUG, "ASN.1: Too long OID value");
108			return -1;
109		}
110		if (oid->len == 0) {
111			/*
112			 * The first octet encodes the first two object
113			 * identifier components in (X*40) + Y formula.
114			 * X = 0..2.
115			 */
116			oid->oid[0] = val / 40;
117			if (oid->oid[0] > 2)
118				oid->oid[0] = 2;
119			oid->oid[1] = val - oid->oid[0] * 40;
120			oid->len = 2;
121		} else
122			oid->oid[oid->len++] = val;
123	}
124
125	return 0;
126}
127
128
129int asn1_get_oid(const u8 *buf, size_t len, struct asn1_oid *oid,
130		 const u8 **next)
131{
132	struct asn1_hdr hdr;
133
134	if (asn1_get_next(buf, len, &hdr) < 0 || hdr.length == 0)
135		return -1;
136
137	if (hdr.class != ASN1_CLASS_UNIVERSAL || hdr.tag != ASN1_TAG_OID) {
138		wpa_printf(MSG_DEBUG, "ASN.1: Expected OID - found class %d "
139			   "tag 0x%x", hdr.class, hdr.tag);
140		return -1;
141	}
142
143	*next = hdr.payload + hdr.length;
144
145	return asn1_parse_oid(hdr.payload, hdr.length, oid);
146}
147
148
149void asn1_oid_to_str(struct asn1_oid *oid, char *buf, size_t len)
150{
151	char *pos = buf;
152	size_t i;
153	int ret;
154
155	if (len == 0)
156		return;
157
158	buf[0] = '\0';
159
160	for (i = 0; i < oid->len; i++) {
161		ret = os_snprintf(pos, buf + len - pos,
162				  "%s%lu",
163				  i == 0 ? "" : ".", oid->oid[i]);
164		if (ret < 0 || ret >= buf + len - pos)
165			break;
166		pos += ret;
167	}
168	buf[len - 1] = '\0';
169}
170
171
172static u8 rotate_bits(u8 octet)
173{
174	int i;
175	u8 res;
176
177	res = 0;
178	for (i = 0; i < 8; i++) {
179		res <<= 1;
180		if (octet & 1)
181			res |= 1;
182		octet >>= 1;
183	}
184
185	return res;
186}
187
188
189unsigned long asn1_bit_string_to_long(const u8 *buf, size_t len)
190{
191	unsigned long val = 0;
192	const u8 *pos = buf;
193
194	/* BER requires that unused bits are zero, so we can ignore the number
195	 * of unused bits */
196	pos++;
197
198	if (len >= 2)
199		val |= rotate_bits(*pos++);
200	if (len >= 3)
201		val |= ((unsigned long) rotate_bits(*pos++)) << 8;
202	if (len >= 4)
203		val |= ((unsigned long) rotate_bits(*pos++)) << 16;
204	if (len >= 5)
205		val |= ((unsigned long) rotate_bits(*pos++)) << 24;
206	if (len >= 6)
207		wpa_printf(MSG_DEBUG, "X509: %s - some bits ignored "
208			   "(BIT STRING length %lu)",
209			   __func__, (unsigned long) len);
210
211	return val;
212}
213