1 /*
2 * libwebsockets - small server side websockets and web server implementation
3 *
4 * Copyright (C) 2010 - 2019 Andy Green <andy@warmcat.com>
5 *
6 * Permission is hereby granted, free of charge, to any person obtaining a copy
7 * of this software and associated documentation files (the "Software"), to
8 * deal in the Software without restriction, including without limitation the
9 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
10 * sell copies of the Software, and to permit persons to whom the Software is
11 * furnished to do so, subject to the following conditions:
12 *
13 * The above copyright notice and this permission notice shall be included in
14 * all copies or substantial portions of the Software.
15 *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
21 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
22 * IN THE SOFTWARE.
23 */
24
25 #include "private-lib-core.h"
26 #include "private-lib-jose-jwe.h"
27
28 int
lws_jwe_encrypt_cbc_hs(struct lws_jwe * jwe,uint8_t * cek,uint8_t * aad,int aad_len)29 lws_jwe_encrypt_cbc_hs(struct lws_jwe *jwe, uint8_t *cek,
30 uint8_t *aad, int aad_len)
31 {
32 int n, hlen = lws_genhmac_size(jwe->jose.enc_alg->hmac_type);
33 uint8_t digest[LWS_GENHASH_LARGEST];
34 struct lws_gencrypto_keyelem el;
35 struct lws_genhmac_ctx hmacctx;
36 struct lws_genaes_ctx aesctx;
37 size_t paddedlen;
38 uint8_t al[8];
39
40 /* Caller must have prepared space for the results */
41
42 if (jwe->jws.map.len[LJWE_ATAG] != (unsigned int)hlen / 2) {
43 lwsl_notice("%s: expected tag len %d, got %d\n", __func__,
44 hlen / 2, jwe->jws.map.len[LJWE_ATAG]);
45 return -1;
46 }
47
48 if (jwe->jws.map.len[LJWE_IV] != 16) {
49 lwsl_notice("expected iv len %d, got %d\n", 16,
50 jwe->jws.map.len[LJWE_IV]);
51 return -1;
52 }
53
54 /* first create the authentication hmac */
55
56 /* JWA Section 5.2.2.1
57 *
58 * 1. The secondary keys MAC_KEY and ENC_KEY are generated from the
59 * input key K as follows. Each of these two keys is an octet
60 * string.
61 *
62 * MAC_KEY consists of the initial MAC_KEY_LEN octets of K, in
63 * order.
64 * ENC_KEY consists of the final ENC_KEY_LEN octets of K, in
65 * order.
66 */
67
68 /*
69 * 2. The IV used is a 128-bit value generated randomly or
70 * pseudorandomly for use in the cipher.
71 */
72 lws_get_random(jwe->jws.context, (void *)jwe->jws.map.buf[LJWE_IV], 16);
73
74 /*
75 * 3. The plaintext is CBC encrypted using PKCS #7 padding using
76 * ENC_KEY as the key and the IV. We denote the ciphertext output
77 * from this step as E.
78 */
79
80 /* second half is the AES ENC_KEY */
81 el.buf = cek + (hlen / 2);
82 el.len = hlen / 2;
83
84 if (lws_genaes_create(&aesctx, LWS_GAESO_ENC, LWS_GAESM_CBC, &el,
85 LWS_GAESP_WITH_PADDING, NULL)) {
86 lwsl_err("%s: lws_genaes_create failed\n", __func__);
87
88 return -1;
89 }
90
91 /*
92 * the plaintext gets delivered to us in LJWE_CTXT, this replaces the
93 * plaintext there with the ciphertext, which will be larger by some
94 * padding bytes
95 */
96 n = lws_genaes_crypt(&aesctx, (uint8_t *)jwe->jws.map.buf[LJWE_CTXT],
97 jwe->jws.map.len[LJWE_CTXT],
98 (uint8_t *)jwe->jws.map.buf[LJWE_CTXT],
99 (uint8_t *)jwe->jws.map.buf[LJWE_IV],
100 NULL, NULL, LWS_AES_CBC_BLOCKLEN);
101 paddedlen = lws_gencrypto_padded_length(LWS_AES_CBC_BLOCKLEN,
102 jwe->jws.map.len[LJWE_CTXT]);
103 jwe->jws.map.len[LJWE_CTXT] = paddedlen;
104 lws_genaes_destroy(&aesctx, (uint8_t *)jwe->jws.map.buf[LJWE_CTXT] +
105 paddedlen - LWS_AES_CBC_BLOCKLEN, LWS_AES_CBC_BLOCKLEN);
106 if (n) {
107 lwsl_err("%s: lws_genaes_crypt failed\n", __func__);
108 return -1;
109 }
110
111 /*
112 * 4. The octet string AL is equal to the number of bits in the
113 * Additional Authenticated Data A expressed as a 64-bit unsigned
114 * big-endian integer.
115 */
116 lws_jwe_be64(aad_len * 8, al);
117
118 /* first half of the CEK is the MAC key */
119 if (lws_genhmac_init(&hmacctx, jwe->jose.enc_alg->hmac_type,
120 cek, hlen / 2))
121 return -1;
122
123 /*
124 * 5. A message Authentication Tag T is computed by applying HMAC
125 * [RFC2104] to the following data, in order:
126 *
127 * - the Additional Authenticated Data A,
128 * - the Initialization Vector IV,
129 * - the ciphertext E computed in the previous step, and
130 * - the octet string AL defined above.
131 *
132 * The string MAC_KEY is used as the MAC key. We denote the output
133 * of the MAC computed in this step as M. The first T_LEN octets of
134 * M are used as T.
135 */
136
137 if (lws_genhmac_update(&hmacctx, aad, aad_len) ||
138 lws_genhmac_update(&hmacctx, jwe->jws.map.buf[LJWE_IV],
139 LWS_JWE_AES_IV_BYTES) ||
140 /* since we encrypted it, this is the ciphertext */
141 lws_genhmac_update(&hmacctx,
142 (uint8_t *)jwe->jws.map.buf[LJWE_CTXT],
143 jwe->jws.map.len[LJWE_CTXT]) ||
144 lws_genhmac_update(&hmacctx, al, 8)) {
145 lwsl_err("%s: hmac computation failed\n", __func__);
146 lws_genhmac_destroy(&hmacctx, NULL);
147 return -1;
148 }
149
150 if (lws_genhmac_destroy(&hmacctx, digest)) {
151 lwsl_err("%s: problem destroying hmac\n", __func__);
152 return -1;
153 }
154
155 /* create tag */
156 memcpy((void *)jwe->jws.map.buf[LJWE_ATAG], digest, hlen / 2);
157
158 return jwe->jws.map.len[LJWE_CTXT];
159 }
160
161 int
lws_jwe_auth_and_decrypt_cbc_hs(struct lws_jwe * jwe,uint8_t * enc_cek,uint8_t * aad,int aad_len)162 lws_jwe_auth_and_decrypt_cbc_hs(struct lws_jwe *jwe, uint8_t *enc_cek,
163 uint8_t *aad, int aad_len)
164 {
165 int n, hlen = lws_genhmac_size(jwe->jose.enc_alg->hmac_type);
166 uint8_t digest[LWS_GENHASH_LARGEST];
167 struct lws_gencrypto_keyelem el;
168 struct lws_genhmac_ctx hmacctx;
169 struct lws_genaes_ctx aesctx;
170 uint8_t al[8];
171
172 /* Some sanity checks on what came in */
173
174 if (jwe->jws.map.len[LJWE_ATAG] != (unsigned int)hlen / 2) {
175 lwsl_notice("%s: expected tag len %d, got %d\n", __func__,
176 hlen / 2, jwe->jws.map.len[LJWE_ATAG]);
177 return -1;
178 }
179
180 if (jwe->jws.map.len[LJWE_IV] != 16) {
181 lwsl_notice("expected iv len %d, got %d\n", 16,
182 jwe->jws.map.len[LJWE_IV]);
183 return -1;
184 }
185
186 /* Prepare to check authentication
187 *
188 * AAD is the b64 JOSE header.
189 *
190 * The octet string AL, which is the number of bits in AAD expressed as
191 * a big-endian 64-bit unsigned integer is:
192 *
193 * [0, 0, 0, 0, 0, 0, 1, 152]
194 *
195 * Concatenate the AAD, the Initialization Vector, the ciphertext, and
196 * the AL value.
197 *
198 */
199
200 lws_jwe_be64(aad_len * 8, al);
201
202 /* first half of enc_cek is the MAC key */
203 if (lws_genhmac_init(&hmacctx, jwe->jose.enc_alg->hmac_type, enc_cek,
204 hlen / 2)) {
205 lwsl_err("%s: lws_genhmac_init fail\n", __func__);
206 return -1;
207 }
208
209 if (lws_genhmac_update(&hmacctx, aad, aad_len) ||
210 lws_genhmac_update(&hmacctx, (uint8_t *)jwe->jws.map.buf[LJWE_IV],
211 jwe->jws.map.len[LJWE_IV]) ||
212 lws_genhmac_update(&hmacctx, (uint8_t *)jwe->jws.map.buf[LJWE_CTXT],
213 jwe->jws.map.len[LJWE_CTXT]) ||
214 lws_genhmac_update(&hmacctx, al, 8)) {
215 lwsl_err("%s: hmac computation failed\n", __func__);
216 lws_genhmac_destroy(&hmacctx, NULL);
217 return -1;
218 }
219
220 if (lws_genhmac_destroy(&hmacctx, digest)) {
221 lwsl_err("%s: problem destroying hmac\n", __func__);
222 return -1;
223 }
224
225 /* first half of digest is the auth tag */
226
227 if (lws_timingsafe_bcmp(digest, jwe->jws.map.buf[LJWE_ATAG], hlen / 2)) {
228 lwsl_err("%s: auth failed: hmac tag (%d) != ATAG (%d)\n",
229 __func__, hlen / 2, jwe->jws.map.len[LJWE_ATAG]);
230 lwsl_hexdump_notice(jwe->jws.map.buf[LJWE_ATAG], hlen / 2);
231 lwsl_hexdump_notice(digest, hlen / 2);
232 return -1;
233 }
234
235 /* second half of enc cek is the CEK KEY */
236 el.buf = enc_cek + (hlen / 2);
237 el.len = hlen / 2;
238
239 if (lws_genaes_create(&aesctx, LWS_GAESO_DEC, LWS_GAESM_CBC,
240 &el, LWS_GAESP_NO_PADDING, NULL)) {
241 lwsl_err("%s: lws_genaes_create failed\n", __func__);
242
243 return -1;
244 }
245
246 n = lws_genaes_crypt(&aesctx, (uint8_t *)jwe->jws.map.buf[LJWE_CTXT],
247 jwe->jws.map.len[LJWE_CTXT],
248 (uint8_t *)jwe->jws.map.buf[LJWE_CTXT],
249 (uint8_t *)jwe->jws.map.buf[LJWE_IV], NULL, NULL, 16);
250
251 /* Strip the PKCS #7 padding */
252
253 if (jwe->jws.map.len[LJWE_CTXT] < LWS_AES_CBC_BLOCKLEN ||
254 jwe->jws.map.len[LJWE_CTXT] <= (unsigned char)jwe->jws.map.buf[LJWE_CTXT]
255 [jwe->jws.map.len[LJWE_CTXT] - 1]) {
256 lwsl_err("%s: invalid padded ciphertext length: %d. Corrupt data?\n",
257 __func__, jwe->jws.map.len[LJWE_CTXT]);
258 return -1;
259 }
260 jwe->jws.map.len[LJWE_CTXT] -= jwe->jws.map.buf[LJWE_CTXT][
261 jwe->jws.map.len[LJWE_CTXT] - 1];
262
263 n |= lws_genaes_destroy(&aesctx, NULL, 0);
264 if (n) {
265 lwsl_err("%s: lws_genaes_crypt failed\n", __func__);
266 return -1;
267 }
268
269 return jwe->jws.map.len[LJWE_CTXT];
270 }
271
272