asn1.c revision c5ec7f57ead87efa365800228aa0b09a12d9e6c4 
1/*
2 * ASN.1 DER parsing
3 * Copyright (c) 2006, Jouni Malinen <j@w1.fi>
4 *
5 * This software may be distributed under the terms of the BSD license.
6 * See README for more details.
7 */
8
9#include "includes.h"
10
11#include "common.h"
12#include "asn1.h"
13
14int asn1_get_next(const u8 *buf, size_t len, struct asn1_hdr *hdr)
15{
16	const u8 *pos, *end;
17	u8 tmp;
18
19	os_memset(hdr, 0, sizeof(*hdr));
20	pos = buf;
21	end = buf + len;
22
23	hdr->identifier = *pos++;
24	hdr->class = hdr->identifier >> 6;
25	hdr->constructed = !!(hdr->identifier & (1 << 5));
26
27	if ((hdr->identifier & 0x1f) == 0x1f) {
28		hdr->tag = 0;
29		do {
30			if (pos >= end) {
31				wpa_printf(MSG_DEBUG, "ASN.1: Identifier "
32					   "underflow");
33				return -1;
34			}
35			tmp = *pos++;
36			wpa_printf(MSG_MSGDUMP, "ASN.1: Extended tag data: "
37				   "0x%02x", tmp);
38			hdr->tag = (hdr->tag << 7) | (tmp & 0x7f);
39		} while (tmp & 0x80);
40	} else
41		hdr->tag = hdr->identifier & 0x1f;
42
43	tmp = *pos++;
44	if (tmp & 0x80) {
45		if (tmp == 0xff) {
46			wpa_printf(MSG_DEBUG, "ASN.1: Reserved length "
47				   "value 0xff used");
48			return -1;
49		}
50		tmp &= 0x7f; /* number of subsequent octets */
51		hdr->length = 0;
52		if (tmp > 4) {
53			wpa_printf(MSG_DEBUG, "ASN.1: Too long length field");
54			return -1;
55		}
56		while (tmp--) {
57			if (pos >= end) {
58				wpa_printf(MSG_DEBUG, "ASN.1: Length "
59					   "underflow");
60				return -1;
61			}
62			hdr->length = (hdr->length << 8) | *pos++;
63		}
64	} else {
65		/* Short form - length 0..127 in one octet */
66		hdr->length = tmp;
67	}
68
69	if (end < pos || hdr->length > (unsigned int) (end - pos)) {
70		wpa_printf(MSG_DEBUG, "ASN.1: Contents underflow");
71		return -1;
72	}
73
74	hdr->payload = pos;
75	return 0;
76}
77
78
79int asn1_parse_oid(const u8 *buf, size_t len, struct asn1_oid *oid)
80{
81	const u8 *pos, *end;
82	unsigned long val;
83	u8 tmp;
84
85	os_memset(oid, 0, sizeof(*oid));
86
87	pos = buf;
88	end = buf + len;
89
90	while (pos < end) {
91		val = 0;
92
93		do {
94			if (pos >= end)
95				return -1;
96			tmp = *pos++;
97			val = (val << 7) | (tmp & 0x7f);
98		} while (tmp & 0x80);
99
100		if (oid->len >= ASN1_MAX_OID_LEN) {
101			wpa_printf(MSG_DEBUG, "ASN.1: Too long OID value");
102			return -1;
103		}
104		if (oid->len == 0) {
105			/*
106			 * The first octet encodes the first two object
107			 * identifier components in (X*40) + Y formula.
108			 * X = 0..2.
109			 */
110			oid->oid[0] = val / 40;
111			if (oid->oid[0] > 2)
112				oid->oid[0] = 2;
113			oid->oid[1] = val - oid->oid[0] * 40;
114			oid->len = 2;
115		} else
116			oid->oid[oid->len++] = val;
117	}
118
119	return 0;
120}
121
122
123int asn1_get_oid(const u8 *buf, size_t len, struct asn1_oid *oid,
124		 const u8 **next)
125{
126	struct asn1_hdr hdr;
127
128	if (asn1_get_next(buf, len, &hdr) < 0 || hdr.length == 0)
129		return -1;
130
131	if (hdr.class != ASN1_CLASS_UNIVERSAL || hdr.tag != ASN1_TAG_OID) {
132		wpa_printf(MSG_DEBUG, "ASN.1: Expected OID - found class %d "
133			   "tag 0x%x", hdr.class, hdr.tag);
134		return -1;
135	}
136
137	*next = hdr.payload + hdr.length;
138
139	return asn1_parse_oid(hdr.payload, hdr.length, oid);
140}
141
142
143void asn1_oid_to_str(struct asn1_oid *oid, char *buf, size_t len)
144{
145	char *pos = buf;
146	size_t i;
147	int ret;
148
149	if (len == 0)
150		return;
151
152	buf[0] = '\0';
153
154	for (i = 0; i < oid->len; i++) {
155		ret = os_snprintf(pos, buf + len - pos,
156				  "%s%lu",
157				  i == 0 ? "" : ".", oid->oid[i]);
158		if (ret < 0 || ret >= buf + len - pos)
159			break;
160		pos += ret;
161	}
162	buf[len - 1] = '\0';
163}
164
165
166static u8 rotate_bits(u8 octet)
167{
168	int i;
169	u8 res;
170
171	res = 0;
172	for (i = 0; i < 8; i++) {
173		res <<= 1;
174		if (octet & 1)
175			res |= 1;
176		octet >>= 1;
177	}
178
179	return res;
180}
181
182
183unsigned long asn1_bit_string_to_long(const u8 *buf, size_t len)
184{
185	unsigned long val = 0;
186	const u8 *pos = buf;
187
188	/* BER requires that unused bits are zero, so we can ignore the number
189	 * of unused bits */
190	pos++;
191
192	if (len >= 2)
193		val |= rotate_bits(*pos++);
194	if (len >= 3)
195		val |= ((unsigned long) rotate_bits(*pos++)) << 8;
196	if (len >= 4)
197		val |= ((unsigned long) rotate_bits(*pos++)) << 16;
198	if (len >= 5)
199		val |= ((unsigned long) rotate_bits(*pos++)) << 24;
200	if (len >= 6)
201		wpa_printf(MSG_DEBUG, "X509: %s - some bits ignored "
202			   "(BIT STRING length %lu)",
203			   __func__, (unsigned long) len);
204
205	return val;
206}
207