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 * GCM initialisation. This does everything except setting the vtable,
29 * which depends on whether this is a context for encrypting or for
30 * decrypting.
31 */
32static void
33gen_gcm_init(br_sslrec_gcm_context *cc,
34	const br_block_ctr_class *bc_impl,
35	const void *key, size_t key_len,
36	br_ghash gh_impl,
37	const void *iv)
38{
39	unsigned char tmp[12];
40
41	cc->seq = 0;
42	bc_impl->init(&cc->bc.vtable, key, key_len);
43	cc->gh = gh_impl;
44	memcpy(cc->iv, iv, sizeof cc->iv);
45	memset(cc->h, 0, sizeof cc->h);
46	memset(tmp, 0, sizeof tmp);
47	bc_impl->run(&cc->bc.vtable, tmp, 0, cc->h, sizeof cc->h);
48}
49
50static void
51in_gcm_init(br_sslrec_gcm_context *cc,
52	const br_block_ctr_class *bc_impl,
53	const void *key, size_t key_len,
54	br_ghash gh_impl,
55	const void *iv)
56{
57	cc->vtable.in = &br_sslrec_in_gcm_vtable;
58	gen_gcm_init(cc, bc_impl, key, key_len, gh_impl, iv);
59}
60
61static int
62gcm_check_length(const br_sslrec_gcm_context *cc, size_t rlen)
63{
64	/*
65	 * GCM adds a fixed overhead:
66	 *   8 bytes for the nonce_explicit (before the ciphertext)
67	 *  16 bytes for the authentication tag (after the ciphertext)
68	 */
69	(void)cc;
70	return rlen >= 24 && rlen <= (16384 + 24);
71}
72
73/*
74 * Compute the authentication tag. The value written in 'tag' must still
75 * be CTR-encrypted.
76 */
77static void
78do_tag(br_sslrec_gcm_context *cc,
79	int record_type, unsigned version,
80	void *data, size_t len, void *tag)
81{
82	unsigned char header[13];
83	unsigned char footer[16];
84
85	/*
86	 * Compute authentication tag. Three elements must be injected in
87	 * sequence, each possibly 0-padded to reach a length multiple
88	 * of the block size: the 13-byte header (sequence number, record
89	 * type, protocol version, record length), the cipher text, and
90	 * the word containing the encodings of the bit lengths of the two
91	 * other elements.
92	 */
93	br_enc64be(header, cc->seq ++);
94	header[8] = (unsigned char)record_type;
95	br_enc16be(header + 9, version);
96	br_enc16be(header + 11, len);
97	br_enc64be(footer, (uint64_t)(sizeof header) << 3);
98	br_enc64be(footer + 8, (uint64_t)len << 3);
99	memset(tag, 0, 16);
100	cc->gh(tag, cc->h, header, sizeof header);
101	cc->gh(tag, cc->h, data, len);
102	cc->gh(tag, cc->h, footer, sizeof footer);
103}
104
105/*
106 * Do CTR encryption. This also does CTR encryption of a single block at
107 * address 'xortag' with the counter value appropriate for the final
108 * processing of the authentication tag.
109 */
110static void
111do_ctr(br_sslrec_gcm_context *cc, const void *nonce, void *data, size_t len,
112	void *xortag)
113{
114	unsigned char iv[12];
115
116	memcpy(iv, cc->iv, 4);
117	memcpy(iv + 4, nonce, 8);
118	cc->bc.vtable->run(&cc->bc.vtable, iv, 2, data, len);
119	cc->bc.vtable->run(&cc->bc.vtable, iv, 1, xortag, 16);
120}
121
122static unsigned char *
123gcm_decrypt(br_sslrec_gcm_context *cc,
124	int record_type, unsigned version, void *data, size_t *data_len)
125{
126	unsigned char *buf;
127	size_t len, u;
128	uint32_t bad;
129	unsigned char tag[16];
130
131	buf = (unsigned char *)data + 8;
132	len = *data_len - 24;
133	do_tag(cc, record_type, version, buf, len, tag);
134	do_ctr(cc, data, buf, len, tag);
135
136	/*
137	 * Compare the computed tag with the value from the record. It
138	 * is possibly useless to do a constant-time comparison here,
139	 * but it does not hurt.
140	 */
141	bad = 0;
142	for (u = 0; u < 16; u ++) {
143		bad |= tag[u] ^ buf[len + u];
144	}
145	if (bad) {
146		return NULL;
147	}
148	*data_len = len;
149	return buf;
150}
151
152/* see bearssl_ssl.h */
153const br_sslrec_in_gcm_class br_sslrec_in_gcm_vtable = {
154	{
155		sizeof(br_sslrec_gcm_context),
156		(int (*)(const br_sslrec_in_class *const *, size_t))
157			&gcm_check_length,
158		(unsigned char *(*)(const br_sslrec_in_class **,
159			int, unsigned, void *, size_t *))
160			&gcm_decrypt
161	},
162	(void (*)(const br_sslrec_in_gcm_class **,
163		const br_block_ctr_class *, const void *, size_t,
164		br_ghash, const void *))
165		&in_gcm_init
166};
167
168static void
169out_gcm_init(br_sslrec_gcm_context *cc,
170	const br_block_ctr_class *bc_impl,
171	const void *key, size_t key_len,
172	br_ghash gh_impl,
173	const void *iv)
174{
175	cc->vtable.out = &br_sslrec_out_gcm_vtable;
176	gen_gcm_init(cc, bc_impl, key, key_len, gh_impl, iv);
177}
178
179static void
180gcm_max_plaintext(const br_sslrec_gcm_context *cc,
181	size_t *start, size_t *end)
182{
183	size_t len;
184
185	(void)cc;
186	*start += 8;
187	len = *end - *start - 16;
188	if (len > 16384) {
189		len = 16384;
190	}
191	*end = *start + len;
192}
193
194static unsigned char *
195gcm_encrypt(br_sslrec_gcm_context *cc,
196	int record_type, unsigned version, void *data, size_t *data_len)
197{
198	unsigned char *buf;
199	size_t u, len;
200	unsigned char tmp[16];
201
202	buf = (unsigned char *)data;
203	len = *data_len;
204	memset(tmp, 0, sizeof tmp);
205	br_enc64be(buf - 8, cc->seq);
206	do_ctr(cc, buf - 8, buf, len, tmp);
207	do_tag(cc, record_type, version, buf, len, buf + len);
208	for (u = 0; u < 16; u ++) {
209		buf[len + u] ^= tmp[u];
210	}
211	len += 24;
212	buf -= 13;
213	buf[0] = (unsigned char)record_type;
214	br_enc16be(buf + 1, version);
215	br_enc16be(buf + 3, len);
216	*data_len = len + 5;
217	return buf;
218}
219
220/* see bearssl_ssl.h */
221const br_sslrec_out_gcm_class br_sslrec_out_gcm_vtable = {
222	{
223		sizeof(br_sslrec_gcm_context),
224		(void (*)(const br_sslrec_out_class *const *,
225			size_t *, size_t *))
226			&gcm_max_plaintext,
227		(unsigned char *(*)(const br_sslrec_out_class **,
228			int, unsigned, void *, size_t *))
229			&gcm_encrypt
230	},
231	(void (*)(const br_sslrec_out_gcm_class **,
232		const br_block_ctr_class *, const void *, size_t,
233		br_ghash, const void *))
234		&out_gcm_init
235};
236