1/*
2 * PKCS #1 (RSA Encryption)
3 * Copyright (c) 2006-2014, 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 "crypto/crypto.h"
13#include "rsa.h"
14#include "asn1.h"
15#include "pkcs1.h"
16
17
18static int pkcs1_generate_encryption_block(u8 block_type, size_t modlen,
19					   const u8 *in, size_t inlen,
20					   u8 *out, size_t *outlen)
21{
22	size_t ps_len;
23	u8 *pos;
24
25	/*
26	 * PKCS #1 v1.5, 8.1:
27	 *
28	 * EB = 00 || BT || PS || 00 || D
29	 * BT = 00 or 01 for private-key operation; 02 for public-key operation
30	 * PS = k-3-||D||; at least eight octets
31	 * (BT=0: PS=0x00, BT=1: PS=0xff, BT=2: PS=pseudorandom non-zero)
32	 * k = length of modulus in octets (modlen)
33	 */
34
35	if (modlen < 12 || modlen > *outlen || inlen > modlen - 11) {
36		wpa_printf(MSG_DEBUG, "PKCS #1: %s - Invalid buffer "
37			   "lengths (modlen=%lu outlen=%lu inlen=%lu)",
38			   __func__, (unsigned long) modlen,
39			   (unsigned long) *outlen,
40			   (unsigned long) inlen);
41		return -1;
42	}
43
44	pos = out;
45	*pos++ = 0x00;
46	*pos++ = block_type; /* BT */
47	ps_len = modlen - inlen - 3;
48	switch (block_type) {
49	case 0:
50		os_memset(pos, 0x00, ps_len);
51		pos += ps_len;
52		break;
53	case 1:
54		os_memset(pos, 0xff, ps_len);
55		pos += ps_len;
56		break;
57	case 2:
58		if (os_get_random(pos, ps_len) < 0) {
59			wpa_printf(MSG_DEBUG, "PKCS #1: %s - Failed to get "
60				   "random data for PS", __func__);
61			return -1;
62		}
63		while (ps_len--) {
64			if (*pos == 0x00)
65				*pos = 0x01;
66			pos++;
67		}
68		break;
69	default:
70		wpa_printf(MSG_DEBUG, "PKCS #1: %s - Unsupported block type "
71			   "%d", __func__, block_type);
72		return -1;
73	}
74	*pos++ = 0x00;
75	os_memcpy(pos, in, inlen); /* D */
76
77	return 0;
78}
79
80
81int pkcs1_encrypt(int block_type, struct crypto_rsa_key *key,
82		  int use_private, const u8 *in, size_t inlen,
83		  u8 *out, size_t *outlen)
84{
85	size_t modlen;
86
87	modlen = crypto_rsa_get_modulus_len(key);
88
89	if (pkcs1_generate_encryption_block(block_type, modlen, in, inlen,
90					    out, outlen) < 0)
91		return -1;
92
93	return crypto_rsa_exptmod(out, modlen, out, outlen, key, use_private);
94}
95
96
97int pkcs1_v15_private_key_decrypt(struct crypto_rsa_key *key,
98				  const u8 *in, size_t inlen,
99				  u8 *out, size_t *outlen)
100{
101	int res;
102	u8 *pos, *end;
103
104	res = crypto_rsa_exptmod(in, inlen, out, outlen, key, 1);
105	if (res)
106		return res;
107
108	if (*outlen < 2 || out[0] != 0 || out[1] != 2)
109		return -1;
110
111	/* Skip PS (pseudorandom non-zero octets) */
112	pos = out + 2;
113	end = out + *outlen;
114	while (*pos && pos < end)
115		pos++;
116	if (pos == end)
117		return -1;
118	if (pos - out - 2 < 8) {
119		/* PKCS #1 v1.5, 8.1: At least eight octets long PS */
120		wpa_printf(MSG_INFO, "LibTomCrypt: Too short padding");
121		return -1;
122	}
123	pos++;
124
125	*outlen -= pos - out;
126
127	/* Strip PKCS #1 header */
128	os_memmove(out, pos, *outlen);
129
130	return 0;
131}
132
133
134int pkcs1_decrypt_public_key(struct crypto_rsa_key *key,
135			     const u8 *crypt, size_t crypt_len,
136			     u8 *plain, size_t *plain_len)
137{
138	size_t len;
139	u8 *pos;
140
141	len = *plain_len;
142	if (crypto_rsa_exptmod(crypt, crypt_len, plain, &len, key, 0) < 0)
143		return -1;
144
145	/*
146	 * PKCS #1 v1.5, 8.1:
147	 *
148	 * EB = 00 || BT || PS || 00 || D
149	 * BT = 00 or 01
150	 * PS = k-3-||D|| times (00 if BT=00) or (FF if BT=01)
151	 * k = length of modulus in octets
152	 *
153	 * Based on 10.1.3, "The block type shall be 01" for a signature.
154	 */
155
156	if (len < 3 + 8 + 16 /* min hash len */ ||
157	    plain[0] != 0x00 || plain[1] != 0x01) {
158		wpa_printf(MSG_INFO, "LibTomCrypt: Invalid signature EB "
159			   "structure");
160		wpa_hexdump_key(MSG_DEBUG, "Signature EB", plain, len);
161		return -1;
162	}
163
164	pos = plain + 3;
165	/* BT = 01 */
166	if (plain[2] != 0xff) {
167		wpa_printf(MSG_INFO, "LibTomCrypt: Invalid signature "
168			   "PS (BT=01)");
169		wpa_hexdump_key(MSG_DEBUG, "Signature EB", plain, len);
170		return -1;
171	}
172	while (pos < plain + len && *pos == 0xff)
173		pos++;
174
175	if (pos - plain - 2 < 8) {
176		/* PKCS #1 v1.5, 8.1: At least eight octets long PS */
177		wpa_printf(MSG_INFO, "LibTomCrypt: Too short signature "
178			   "padding");
179		wpa_hexdump_key(MSG_DEBUG, "Signature EB", plain, len);
180		return -1;
181	}
182
183	if (pos + 16 /* min hash len */ >= plain + len || *pos != 0x00) {
184		wpa_printf(MSG_INFO, "LibTomCrypt: Invalid signature EB "
185			   "structure (2)");
186		wpa_hexdump_key(MSG_DEBUG, "Signature EB", plain, len);
187		return -1;
188	}
189	pos++;
190	len -= pos - plain;
191
192	/* Strip PKCS #1 header */
193	os_memmove(plain, pos, len);
194	*plain_len = len;
195
196	return 0;
197}
198
199
200int pkcs1_v15_sig_ver(struct crypto_public_key *pk,
201		      const u8 *s, size_t s_len,
202		      const struct asn1_oid *hash_alg,
203		      const u8 *hash, size_t hash_len)
204{
205	int res;
206	u8 *decrypted;
207	size_t decrypted_len;
208	const u8 *pos, *end, *next, *da_end;
209	struct asn1_hdr hdr;
210	struct asn1_oid oid;
211
212	decrypted = os_malloc(s_len);
213	if (decrypted == NULL)
214		return -1;
215	decrypted_len = s_len;
216	res = crypto_public_key_decrypt_pkcs1(pk, s, s_len, decrypted,
217					      &decrypted_len);
218	if (res < 0) {
219		wpa_printf(MSG_INFO, "PKCS #1: RSA decrypt failed");
220		os_free(decrypted);
221		return -1;
222	}
223	wpa_hexdump(MSG_DEBUG, "Decrypted(S)", decrypted, decrypted_len);
224
225	/*
226	 * PKCS #1 v1.5, 10.1.2:
227	 *
228	 * DigestInfo ::= SEQUENCE {
229	 *     digestAlgorithm DigestAlgorithmIdentifier,
230	 *     digest Digest
231	 * }
232	 *
233	 * DigestAlgorithmIdentifier ::= AlgorithmIdentifier
234	 *
235	 * Digest ::= OCTET STRING
236	 *
237	 */
238	if (asn1_get_next(decrypted, decrypted_len, &hdr) < 0 ||
239	    !asn1_is_sequence(&hdr)) {
240		asn1_unexpected(&hdr,
241				"PKCS #1: Expected SEQUENCE (DigestInfo)");
242		os_free(decrypted);
243		return -1;
244	}
245	wpa_hexdump(MSG_MSGDUMP, "PKCS #1: DigestInfo",
246		    hdr.payload, hdr.length);
247
248	pos = hdr.payload;
249	end = pos + hdr.length;
250
251	/*
252	 * X.509:
253	 * AlgorithmIdentifier ::= SEQUENCE {
254	 *     algorithm            OBJECT IDENTIFIER,
255	 *     parameters           ANY DEFINED BY algorithm OPTIONAL
256	 * }
257	 */
258
259	if (asn1_get_next(pos, end - pos, &hdr) < 0 ||
260	    !asn1_is_sequence(&hdr)) {
261		asn1_unexpected(&hdr,
262				"PKCS #1: Expected SEQUENCE (AlgorithmIdentifier)");
263		os_free(decrypted);
264		return -1;
265	}
266	wpa_hexdump(MSG_MSGDUMP, "PKCS #1: DigestAlgorithmIdentifier",
267		    hdr.payload, hdr.length);
268	da_end = hdr.payload + hdr.length;
269
270	if (asn1_get_oid(hdr.payload, hdr.length, &oid, &next)) {
271		wpa_printf(MSG_DEBUG,
272			   "PKCS #1: Failed to parse digestAlgorithm");
273		os_free(decrypted);
274		return -1;
275	}
276	wpa_hexdump(MSG_MSGDUMP, "PKCS #1: Digest algorithm parameters",
277		    next, da_end - next);
278
279	/*
280	 * RFC 5754: The correct encoding for the SHA2 algorithms would be to
281	 * omit the parameters, but there are implementation that encode these
282	 * as a NULL element. Allow these two cases and reject anything else.
283	 */
284	if (da_end > next &&
285	    (asn1_get_next(next, da_end - next, &hdr) < 0 ||
286	     !asn1_is_null(&hdr) ||
287	     hdr.payload + hdr.length != da_end)) {
288		wpa_printf(MSG_DEBUG,
289			   "PKCS #1: Unexpected digest algorithm parameters");
290		os_free(decrypted);
291		return -1;
292	}
293
294	if (!asn1_oid_equal(&oid, hash_alg)) {
295		char txt[100], txt2[100];
296		asn1_oid_to_str(&oid, txt, sizeof(txt));
297		asn1_oid_to_str(hash_alg, txt2, sizeof(txt2));
298		wpa_printf(MSG_DEBUG,
299			   "PKCS #1: Hash alg OID mismatch: was %s, expected %s",
300			   txt, txt2);
301		os_free(decrypted);
302		return -1;
303	}
304
305	/* Digest ::= OCTET STRING */
306	pos = da_end;
307
308	if (asn1_get_next(pos, end - pos, &hdr) < 0 ||
309	    !asn1_is_octetstring(&hdr)) {
310		asn1_unexpected(&hdr,
311				"PKCS #1: Expected OCTETSTRING (Digest)");
312		os_free(decrypted);
313		return -1;
314	}
315	wpa_hexdump(MSG_MSGDUMP, "PKCS #1: Decrypted Digest",
316		    hdr.payload, hdr.length);
317
318	if (hdr.length != hash_len ||
319	    os_memcmp_const(hdr.payload, hash, hdr.length) != 0) {
320		wpa_printf(MSG_INFO, "PKCS #1: Digest value does not match calculated hash");
321		os_free(decrypted);
322		return -1;
323	}
324
325	os_free(decrypted);
326
327	if (hdr.payload + hdr.length != decrypted + decrypted_len) {
328		wpa_printf(MSG_INFO,
329			   "PKCS #1: Extra data after signature - reject");
330
331		wpa_hexdump(MSG_DEBUG, "PKCS #1: Extra data",
332			    hdr.payload + hdr.length,
333			    decrypted + decrypted_len - hdr.payload -
334			    hdr.length);
335		return -1;
336	}
337
338	return 0;
339}
340