Line data Source code
1 : /*
2 : * EAP server/peer: EAP-pwd shared routines
3 : * Copyright (c) 2010, Dan Harkins <dharkins@lounge.org>
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 : #include "common.h"
11 : #include "crypto/sha256.h"
12 : #include "crypto/crypto.h"
13 : #include "eap_defs.h"
14 : #include "eap_pwd_common.h"
15 :
16 : /* The random function H(x) = HMAC-SHA256(0^32, x) */
17 123 : struct crypto_hash * eap_pwd_h_init(void)
18 : {
19 : u8 allzero[SHA256_MAC_LEN];
20 123 : os_memset(allzero, 0, SHA256_MAC_LEN);
21 123 : return crypto_hash_init(CRYPTO_HASH_ALG_HMAC_SHA256, allzero,
22 : SHA256_MAC_LEN);
23 : }
24 :
25 :
26 661 : void eap_pwd_h_update(struct crypto_hash *hash, const u8 *data, size_t len)
27 : {
28 661 : crypto_hash_update(hash, data, len);
29 661 : }
30 :
31 :
32 123 : void eap_pwd_h_final(struct crypto_hash *hash, u8 *digest)
33 : {
34 123 : size_t len = SHA256_MAC_LEN;
35 123 : crypto_hash_finish(hash, digest, &len);
36 123 : }
37 :
38 :
39 : /* a counter-based KDF based on NIST SP800-108 */
40 61 : static int eap_pwd_kdf(const u8 *key, size_t keylen, const u8 *label,
41 : size_t labellen, u8 *result, size_t resultbitlen)
42 : {
43 : struct crypto_hash *hash;
44 : u8 digest[SHA256_MAC_LEN];
45 : u16 i, ctr, L;
46 61 : size_t resultbytelen, len = 0, mdlen;
47 :
48 61 : resultbytelen = (resultbitlen + 7) / 8;
49 61 : ctr = 0;
50 61 : L = htons(resultbitlen);
51 261 : while (len < resultbytelen) {
52 139 : ctr++;
53 139 : i = htons(ctr);
54 139 : hash = crypto_hash_init(CRYPTO_HASH_ALG_HMAC_SHA256,
55 : key, keylen);
56 139 : if (hash == NULL)
57 0 : return -1;
58 139 : if (ctr > 1)
59 78 : crypto_hash_update(hash, digest, SHA256_MAC_LEN);
60 139 : crypto_hash_update(hash, (u8 *) &i, sizeof(u16));
61 139 : crypto_hash_update(hash, label, labellen);
62 139 : crypto_hash_update(hash, (u8 *) &L, sizeof(u16));
63 139 : mdlen = SHA256_MAC_LEN;
64 139 : if (crypto_hash_finish(hash, digest, &mdlen) < 0)
65 0 : return -1;
66 139 : if ((len + mdlen) > resultbytelen)
67 18 : os_memcpy(result + len, digest, resultbytelen - len);
68 : else
69 121 : os_memcpy(result + len, digest, mdlen);
70 139 : len += mdlen;
71 : }
72 :
73 : /* since we're expanding to a bit length, mask off the excess */
74 61 : if (resultbitlen % 8) {
75 8 : u8 mask = 0xff;
76 8 : mask <<= (8 - (resultbitlen % 8));
77 8 : result[resultbytelen - 1] &= mask;
78 : }
79 :
80 61 : return 0;
81 : }
82 :
83 :
84 : /*
85 : * compute a "random" secret point on an elliptic curve based
86 : * on the password and identities.
87 : */
88 23 : int compute_password_element(EAP_PWD_group *grp, u16 num,
89 : u8 *password, int password_len,
90 : u8 *id_server, int id_server_len,
91 : u8 *id_peer, int id_peer_len, u8 *token)
92 : {
93 23 : BIGNUM *x_candidate = NULL, *rnd = NULL, *cofactor = NULL;
94 : struct crypto_hash *hash;
95 23 : unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr;
96 23 : int nid, is_odd, ret = 0;
97 : size_t primebytelen, primebitlen;
98 :
99 23 : switch (num) { /* from IANA registry for IKE D-H groups */
100 : case 19:
101 14 : nid = NID_X9_62_prime256v1;
102 14 : break;
103 : case 20:
104 2 : nid = NID_secp384r1;
105 2 : break;
106 : case 21:
107 2 : nid = NID_secp521r1;
108 2 : break;
109 : case 25:
110 2 : nid = NID_X9_62_prime192v1;
111 2 : break;
112 : case 26:
113 2 : nid = NID_secp224r1;
114 2 : break;
115 : default:
116 1 : wpa_printf(MSG_INFO, "EAP-pwd: unsupported group %d", num);
117 1 : return -1;
118 : }
119 :
120 22 : grp->pwe = NULL;
121 22 : grp->order = NULL;
122 22 : grp->prime = NULL;
123 :
124 22 : if ((grp->group = EC_GROUP_new_by_curve_name(nid)) == NULL) {
125 0 : wpa_printf(MSG_INFO, "EAP-pwd: unable to create EC_GROUP");
126 0 : goto fail;
127 : }
128 :
129 22 : if (((rnd = BN_new()) == NULL) ||
130 22 : ((cofactor = BN_new()) == NULL) ||
131 44 : ((grp->pwe = EC_POINT_new(grp->group)) == NULL) ||
132 44 : ((grp->order = BN_new()) == NULL) ||
133 44 : ((grp->prime = BN_new()) == NULL) ||
134 : ((x_candidate = BN_new()) == NULL)) {
135 0 : wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums");
136 0 : goto fail;
137 : }
138 :
139 22 : if (!EC_GROUP_get_curve_GFp(grp->group, grp->prime, NULL, NULL, NULL))
140 : {
141 0 : wpa_printf(MSG_INFO, "EAP-pwd: unable to get prime for GFp "
142 : "curve");
143 0 : goto fail;
144 : }
145 22 : if (!EC_GROUP_get_order(grp->group, grp->order, NULL)) {
146 0 : wpa_printf(MSG_INFO, "EAP-pwd: unable to get order for curve");
147 0 : goto fail;
148 : }
149 22 : if (!EC_GROUP_get_cofactor(grp->group, cofactor, NULL)) {
150 0 : wpa_printf(MSG_INFO, "EAP-pwd: unable to get cofactor for "
151 : "curve");
152 0 : goto fail;
153 : }
154 22 : primebitlen = BN_num_bits(grp->prime);
155 22 : primebytelen = BN_num_bytes(grp->prime);
156 22 : if ((prfbuf = os_malloc(primebytelen)) == NULL) {
157 0 : wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf "
158 : "buffer");
159 0 : goto fail;
160 : }
161 22 : os_memset(prfbuf, 0, primebytelen);
162 22 : ctr = 0;
163 : while (1) {
164 41 : if (ctr > 30) {
165 0 : wpa_printf(MSG_INFO, "EAP-pwd: unable to find random "
166 : "point on curve for group %d, something's "
167 : "fishy", num);
168 0 : goto fail;
169 : }
170 41 : ctr++;
171 :
172 : /*
173 : * compute counter-mode password value and stretch to prime
174 : * pwd-seed = H(token | peer-id | server-id | password |
175 : * counter)
176 : */
177 41 : hash = eap_pwd_h_init();
178 41 : if (hash == NULL)
179 0 : goto fail;
180 41 : eap_pwd_h_update(hash, token, sizeof(u32));
181 41 : eap_pwd_h_update(hash, id_peer, id_peer_len);
182 41 : eap_pwd_h_update(hash, id_server, id_server_len);
183 41 : eap_pwd_h_update(hash, password, password_len);
184 41 : eap_pwd_h_update(hash, &ctr, sizeof(ctr));
185 41 : eap_pwd_h_final(hash, pwe_digest);
186 :
187 41 : BN_bin2bn(pwe_digest, SHA256_MAC_LEN, rnd);
188 :
189 41 : if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN,
190 : (u8 *) "EAP-pwd Hunting And Pecking",
191 : os_strlen("EAP-pwd Hunting And Pecking"),
192 : prfbuf, primebitlen) < 0)
193 0 : goto fail;
194 :
195 41 : BN_bin2bn(prfbuf, primebytelen, x_candidate);
196 :
197 : /*
198 : * eap_pwd_kdf() returns a string of bits 0..primebitlen but
199 : * BN_bin2bn will treat that string of bits as a big endian
200 : * number. If the primebitlen is not an even multiple of 8
201 : * then excessive bits-- those _after_ primebitlen-- so now
202 : * we have to shift right the amount we masked off.
203 : */
204 41 : if (primebitlen % 8)
205 8 : BN_rshift(x_candidate, x_candidate,
206 : (8 - (primebitlen % 8)));
207 :
208 41 : if (BN_ucmp(x_candidate, grp->prime) >= 0)
209 0 : continue;
210 :
211 41 : wpa_hexdump(MSG_DEBUG, "EAP-pwd: x_candidate",
212 : prfbuf, primebytelen);
213 :
214 : /*
215 : * need to unambiguously identify the solution, if there is
216 : * one...
217 : */
218 41 : if (BN_is_odd(rnd))
219 23 : is_odd = 1;
220 : else
221 18 : is_odd = 0;
222 :
223 : /*
224 : * solve the quadratic equation, if it's not solvable then we
225 : * don't have a point
226 : */
227 41 : if (!EC_POINT_set_compressed_coordinates_GFp(grp->group,
228 : grp->pwe,
229 : x_candidate,
230 : is_odd, NULL))
231 19 : continue;
232 : /*
233 : * If there's a solution to the equation then the point must be
234 : * on the curve so why check again explicitly? OpenSSL code
235 : * says this is required by X9.62. We're not X9.62 but it can't
236 : * hurt just to be sure.
237 : */
238 22 : if (!EC_POINT_is_on_curve(grp->group, grp->pwe, NULL)) {
239 0 : wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve");
240 0 : continue;
241 : }
242 :
243 22 : if (BN_cmp(cofactor, BN_value_one())) {
244 : /* make sure the point is not in a small sub-group */
245 0 : if (!EC_POINT_mul(grp->group, grp->pwe, NULL, grp->pwe,
246 : cofactor, NULL)) {
247 0 : wpa_printf(MSG_INFO, "EAP-pwd: cannot "
248 : "multiply generator by order");
249 0 : continue;
250 : }
251 0 : if (EC_POINT_is_at_infinity(grp->group, grp->pwe)) {
252 0 : wpa_printf(MSG_INFO, "EAP-pwd: point is at "
253 : "infinity");
254 0 : continue;
255 : }
256 : }
257 : /* if we got here then we have a new generator. */
258 22 : break;
259 19 : }
260 22 : wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %d tries", ctr);
261 22 : grp->group_num = num;
262 : if (0) {
263 : fail:
264 0 : EC_GROUP_free(grp->group);
265 0 : grp->group = NULL;
266 0 : EC_POINT_free(grp->pwe);
267 0 : grp->pwe = NULL;
268 0 : BN_free(grp->order);
269 0 : grp->order = NULL;
270 0 : BN_free(grp->prime);
271 0 : grp->prime = NULL;
272 0 : ret = 1;
273 : }
274 : /* cleanliness and order.... */
275 22 : BN_free(cofactor);
276 22 : BN_free(x_candidate);
277 22 : BN_free(rnd);
278 22 : os_free(prfbuf);
279 :
280 22 : return ret;
281 : }
282 :
283 :
284 20 : int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, BIGNUM *k,
285 : BIGNUM *peer_scalar, BIGNUM *server_scalar,
286 : u8 *confirm_peer, u8 *confirm_server,
287 : u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id)
288 : {
289 : struct crypto_hash *hash;
290 : u8 mk[SHA256_MAC_LEN], *cruft;
291 : u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN];
292 : int offset;
293 :
294 20 : if ((cruft = os_malloc(BN_num_bytes(grp->prime))) == NULL)
295 0 : return -1;
296 :
297 : /*
298 : * first compute the session-id = TypeCode | H(ciphersuite | scal_p |
299 : * scal_s)
300 : */
301 20 : session_id[0] = EAP_TYPE_PWD;
302 20 : hash = eap_pwd_h_init();
303 20 : if (hash == NULL) {
304 0 : os_free(cruft);
305 0 : return -1;
306 : }
307 20 : eap_pwd_h_update(hash, (u8 *) ciphersuite, sizeof(u32));
308 20 : offset = BN_num_bytes(grp->order) - BN_num_bytes(peer_scalar);
309 20 : os_memset(cruft, 0, BN_num_bytes(grp->prime));
310 20 : BN_bn2bin(peer_scalar, cruft + offset);
311 20 : eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order));
312 20 : offset = BN_num_bytes(grp->order) - BN_num_bytes(server_scalar);
313 20 : os_memset(cruft, 0, BN_num_bytes(grp->prime));
314 20 : BN_bn2bin(server_scalar, cruft + offset);
315 20 : eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order));
316 20 : eap_pwd_h_final(hash, &session_id[1]);
317 :
318 : /* then compute MK = H(k | confirm-peer | confirm-server) */
319 20 : hash = eap_pwd_h_init();
320 20 : if (hash == NULL) {
321 0 : os_free(cruft);
322 0 : return -1;
323 : }
324 20 : offset = BN_num_bytes(grp->prime) - BN_num_bytes(k);
325 20 : os_memset(cruft, 0, BN_num_bytes(grp->prime));
326 20 : BN_bn2bin(k, cruft + offset);
327 20 : eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->prime));
328 20 : os_free(cruft);
329 20 : eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN);
330 20 : eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN);
331 20 : eap_pwd_h_final(hash, mk);
332 :
333 : /* stretch the mk with the session-id to get MSK | EMSK */
334 20 : if (eap_pwd_kdf(mk, SHA256_MAC_LEN,
335 : session_id, SHA256_MAC_LEN + 1,
336 : msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) {
337 0 : return -1;
338 : }
339 :
340 20 : os_memcpy(msk, msk_emsk, EAP_MSK_LEN);
341 20 : os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN);
342 :
343 20 : return 1;
344 : }
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