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 "utils/const_time.h"
12 #include "common/dragonfly.h"
13 #include "crypto/sha256.h"
14 #include "crypto/crypto.h"
15 #include "eap_defs.h"
16 #include "eap_pwd_common.h"
17
18 #define MAX_ECC_PRIME_LEN 66
19
20
21 /* The random function H(x) = HMAC-SHA256(0^32, x) */
eap_pwd_h_init(void)22 struct crypto_hash * eap_pwd_h_init(void)
23 {
24 u8 allzero[SHA256_MAC_LEN];
25 os_memset(allzero, 0, SHA256_MAC_LEN);
26 return crypto_hash_init(CRYPTO_HASH_ALG_HMAC_SHA256, allzero,
27 SHA256_MAC_LEN);
28 }
29
30
eap_pwd_h_update(struct crypto_hash * hash,const u8 * data,size_t len)31 void eap_pwd_h_update(struct crypto_hash *hash, const u8 *data, size_t len)
32 {
33 crypto_hash_update(hash, data, len);
34 }
35
36
eap_pwd_h_final(struct crypto_hash * hash,u8 * digest)37 void eap_pwd_h_final(struct crypto_hash *hash, u8 *digest)
38 {
39 size_t len = SHA256_MAC_LEN;
40 crypto_hash_finish(hash, digest, &len);
41 }
42
43
44 /* a counter-based KDF based on NIST SP800-108 */
eap_pwd_kdf(const u8 * key,size_t keylen,const u8 * label,size_t labellen,u8 * result,size_t resultbitlen)45 static int eap_pwd_kdf(const u8 *key, size_t keylen, const u8 *label,
46 size_t labellen, u8 *result, size_t resultbitlen)
47 {
48 struct crypto_hash *hash;
49 u8 digest[SHA256_MAC_LEN];
50 u16 i, ctr, L;
51 size_t resultbytelen, len = 0, mdlen;
52
53 resultbytelen = (resultbitlen + 7) / 8;
54 ctr = 0;
55 L = htons(resultbitlen);
56 while (len < resultbytelen) {
57 ctr++;
58 i = htons(ctr);
59 hash = crypto_hash_init(CRYPTO_HASH_ALG_HMAC_SHA256,
60 key, keylen);
61 if (hash == NULL)
62 return -1;
63 if (ctr > 1)
64 crypto_hash_update(hash, digest, SHA256_MAC_LEN);
65 crypto_hash_update(hash, (u8 *) &i, sizeof(u16));
66 crypto_hash_update(hash, label, labellen);
67 crypto_hash_update(hash, (u8 *) &L, sizeof(u16));
68 mdlen = SHA256_MAC_LEN;
69 if (crypto_hash_finish(hash, digest, &mdlen) < 0)
70 return -1;
71 if ((len + mdlen) > resultbytelen)
72 os_memcpy(result + len, digest, resultbytelen - len);
73 else
74 os_memcpy(result + len, digest, mdlen);
75 len += mdlen;
76 }
77
78 /* since we're expanding to a bit length, mask off the excess */
79 if (resultbitlen % 8) {
80 u8 mask = 0xff;
81 mask <<= (8 - (resultbitlen % 8));
82 result[resultbytelen - 1] &= mask;
83 }
84
85 return 0;
86 }
87
88
get_eap_pwd_group(u16 num)89 EAP_PWD_group * get_eap_pwd_group(u16 num)
90 {
91 EAP_PWD_group *grp;
92
93 if (!dragonfly_suitable_group(num, 1)) {
94 wpa_printf(MSG_INFO, "EAP-pwd: unsuitable group %u", num);
95 return NULL;
96 }
97 grp = os_zalloc(sizeof(EAP_PWD_group));
98 if (!grp)
99 return NULL;
100 grp->group = crypto_ec_init(num);
101 if (!grp->group) {
102 wpa_printf(MSG_INFO, "EAP-pwd: unable to create EC group");
103 os_free(grp);
104 return NULL;
105 }
106
107 grp->group_num = num;
108 wpa_printf(MSG_INFO, "EAP-pwd: provisioned group %d", num);
109
110 return grp;
111 }
112
113
114 /*
115 * compute a "random" secret point on an elliptic curve based
116 * on the password and identities.
117 */
compute_password_element(EAP_PWD_group * grp,u16 num,const u8 * password,size_t password_len,const u8 * id_server,size_t id_server_len,const u8 * id_peer,size_t id_peer_len,const u8 * token)118 int compute_password_element(EAP_PWD_group *grp, u16 num,
119 const u8 *password, size_t password_len,
120 const u8 *id_server, size_t id_server_len,
121 const u8 *id_peer, size_t id_peer_len,
122 const u8 *token)
123 {
124 struct crypto_bignum *qr = NULL, *qnr = NULL;
125 u8 qr_bin[MAX_ECC_PRIME_LEN];
126 u8 qnr_bin[MAX_ECC_PRIME_LEN];
127 u8 qr_or_qnr_bin[MAX_ECC_PRIME_LEN];
128 u8 x_bin[MAX_ECC_PRIME_LEN];
129 u8 prime_bin[MAX_ECC_PRIME_LEN];
130 struct crypto_bignum *tmp2 = NULL;
131 struct crypto_hash *hash;
132 unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr;
133 int ret = 0, res;
134 u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_*
135 * mask */
136 size_t primebytelen = 0, primebitlen;
137 struct crypto_bignum *x_candidate = NULL;
138 const struct crypto_bignum *prime;
139 u8 found_ctr = 0, is_odd = 0;
140 int cmp_prime;
141 unsigned int in_range;
142
143 if (grp->pwe)
144 return -1;
145
146 os_memset(x_bin, 0, sizeof(x_bin));
147
148 prime = crypto_ec_get_prime(grp->group);
149 primebitlen = crypto_ec_prime_len_bits(grp->group);
150 primebytelen = crypto_ec_prime_len(grp->group);
151 if (crypto_bignum_to_bin(prime, prime_bin, sizeof(prime_bin),
152 primebytelen) < 0)
153 return -1;
154 grp->pwe = crypto_ec_point_init(grp->group);
155 if (!grp->pwe) {
156 wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums");
157 goto fail;
158 }
159
160 if ((prfbuf = os_malloc(primebytelen)) == NULL) {
161 wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf "
162 "buffer");
163 goto fail;
164 }
165
166 /* get a random quadratic residue and nonresidue */
167 if (dragonfly_get_random_qr_qnr(prime, &qr, &qnr) < 0 ||
168 crypto_bignum_to_bin(qr, qr_bin, sizeof(qr_bin),
169 primebytelen) < 0 ||
170 crypto_bignum_to_bin(qnr, qnr_bin, sizeof(qnr_bin),
171 primebytelen) < 0)
172 goto fail;
173
174 os_memset(prfbuf, 0, primebytelen);
175 ctr = 0;
176
177 /*
178 * Run through the hunting-and-pecking loop 40 times to mask the time
179 * necessary to find PWE. The odds of PWE not being found in 40 loops is
180 * roughly 1 in 1 trillion.
181 */
182 while (ctr < 40) {
183 ctr++;
184
185 /*
186 * compute counter-mode password value and stretch to prime
187 * pwd-seed = H(token | peer-id | server-id | password |
188 * counter)
189 */
190 hash = eap_pwd_h_init();
191 if (hash == NULL)
192 goto fail;
193 eap_pwd_h_update(hash, token, sizeof(u32));
194 eap_pwd_h_update(hash, id_peer, id_peer_len);
195 eap_pwd_h_update(hash, id_server, id_server_len);
196 eap_pwd_h_update(hash, password, password_len);
197 eap_pwd_h_update(hash, &ctr, sizeof(ctr));
198 eap_pwd_h_final(hash, pwe_digest);
199
200 is_odd = const_time_select_u8(
201 found, is_odd, pwe_digest[SHA256_MAC_LEN - 1] & 0x01);
202 if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN,
203 (u8 *) "EAP-pwd Hunting And Pecking",
204 os_strlen("EAP-pwd Hunting And Pecking"),
205 prfbuf, primebitlen) < 0)
206 goto fail;
207 if (primebitlen % 8)
208 buf_shift_right(prfbuf, primebytelen,
209 8 - primebitlen % 8);
210 cmp_prime = const_time_memcmp(prfbuf, prime_bin, primebytelen);
211 /* Create a const_time mask for selection based on prf result
212 * being smaller than prime. */
213 in_range = const_time_fill_msb((unsigned int) cmp_prime);
214 /* The algorithm description would skip the next steps if
215 * cmp_prime >= 0, but go through them regardless to minimize
216 * externally observable differences in behavior. */
217
218 crypto_bignum_deinit(x_candidate, 1);
219 x_candidate = crypto_bignum_init_set(prfbuf, primebytelen);
220 if (!x_candidate) {
221 wpa_printf(MSG_INFO,
222 "EAP-pwd: unable to create x_candidate");
223 goto fail;
224 }
225
226 wpa_hexdump_key(MSG_DEBUG, "EAP-pwd: x_candidate",
227 prfbuf, primebytelen);
228 const_time_select_bin(found, x_bin, prfbuf, primebytelen,
229 x_bin);
230
231 /*
232 * compute y^2 using the equation of the curve
233 *
234 * y^2 = x^3 + ax + b
235 */
236 crypto_bignum_deinit(tmp2, 1);
237 tmp2 = crypto_ec_point_compute_y_sqr(grp->group, x_candidate);
238 if (!tmp2)
239 goto fail;
240
241 res = dragonfly_is_quadratic_residue_blind(grp->group, qr_bin,
242 qnr_bin, tmp2);
243 if (res < 0)
244 goto fail;
245 found_ctr = const_time_select_u8(found, found_ctr, ctr);
246 /* found is 0 or 0xff here and res is 0 or 1. Bitwise OR of them
247 * (with res converted to 0/0xff and masked with prf being below
248 * prime) handles this in constant time.
249 */
250 found |= (res & in_range) * 0xff;
251 }
252 if (found == 0) {
253 wpa_printf(MSG_INFO,
254 "EAP-pwd: unable to find random point on curve for group %d, something's fishy",
255 num);
256 goto fail;
257 }
258
259 /*
260 * We know x_candidate is a quadratic residue so set it here.
261 */
262 crypto_bignum_deinit(x_candidate, 1);
263 x_candidate = crypto_bignum_init_set(x_bin, primebytelen);
264 if (!x_candidate ||
265 crypto_ec_point_solve_y_coord(grp->group, grp->pwe, x_candidate,
266 is_odd) != 0) {
267 wpa_printf(MSG_INFO, "EAP-pwd: Could not solve for y");
268 goto fail;
269 }
270
271 /*
272 * If there's a solution to the equation then the point must be on the
273 * curve so why check again explicitly? OpenSSL code says this is
274 * required by X9.62. We're not X9.62 but it can't hurt just to be sure.
275 */
276 if (!crypto_ec_point_is_on_curve(grp->group, grp->pwe)) {
277 wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve");
278 goto fail;
279 }
280
281 wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %02d tries", found_ctr);
282
283 if (0) {
284 fail:
285 crypto_ec_point_deinit(grp->pwe, 1);
286 grp->pwe = NULL;
287 ret = 1;
288 }
289 /* cleanliness and order.... */
290 crypto_bignum_deinit(x_candidate, 1);
291 crypto_bignum_deinit(tmp2, 1);
292 crypto_bignum_deinit(qr, 1);
293 crypto_bignum_deinit(qnr, 1);
294 bin_clear_free(prfbuf, primebytelen);
295 os_memset(qr_bin, 0, sizeof(qr_bin));
296 os_memset(qnr_bin, 0, sizeof(qnr_bin));
297 os_memset(qr_or_qnr_bin, 0, sizeof(qr_or_qnr_bin));
298 os_memset(pwe_digest, 0, sizeof(pwe_digest));
299
300 return ret;
301 }
302
303
compute_keys(EAP_PWD_group * grp,const struct crypto_bignum * k,const struct crypto_bignum * peer_scalar,const struct crypto_bignum * server_scalar,const u8 * confirm_peer,const u8 * confirm_server,const u32 * ciphersuite,u8 * msk,u8 * emsk,u8 * session_id)304 int compute_keys(EAP_PWD_group *grp, const struct crypto_bignum *k,
305 const struct crypto_bignum *peer_scalar,
306 const struct crypto_bignum *server_scalar,
307 const u8 *confirm_peer, const u8 *confirm_server,
308 const u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id)
309 {
310 struct crypto_hash *hash;
311 u8 mk[SHA256_MAC_LEN], *cruft;
312 u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN];
313 size_t prime_len, order_len;
314
315 prime_len = crypto_ec_prime_len(grp->group);
316 order_len = crypto_ec_order_len(grp->group);
317
318 cruft = os_malloc(prime_len);
319 if (!cruft)
320 return -1;
321
322 /*
323 * first compute the session-id = TypeCode | H(ciphersuite | scal_p |
324 * scal_s)
325 */
326 session_id[0] = EAP_TYPE_PWD;
327 hash = eap_pwd_h_init();
328 if (hash == NULL) {
329 os_free(cruft);
330 return -1;
331 }
332 eap_pwd_h_update(hash, (const u8 *) ciphersuite, sizeof(u32));
333 crypto_bignum_to_bin(peer_scalar, cruft, order_len, order_len);
334 eap_pwd_h_update(hash, cruft, order_len);
335 crypto_bignum_to_bin(server_scalar, cruft, order_len, order_len);
336 eap_pwd_h_update(hash, cruft, order_len);
337 eap_pwd_h_final(hash, &session_id[1]);
338
339 /* then compute MK = H(k | confirm-peer | confirm-server) */
340 hash = eap_pwd_h_init();
341 if (hash == NULL) {
342 os_free(cruft);
343 return -1;
344 }
345 crypto_bignum_to_bin(k, cruft, prime_len, prime_len);
346 eap_pwd_h_update(hash, cruft, prime_len);
347 os_free(cruft);
348 eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN);
349 eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN);
350 eap_pwd_h_final(hash, mk);
351
352 /* stretch the mk with the session-id to get MSK | EMSK */
353 if (eap_pwd_kdf(mk, SHA256_MAC_LEN,
354 session_id, SHA256_MAC_LEN + 1,
355 msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) {
356 return -1;
357 }
358
359 os_memcpy(msk, msk_emsk, EAP_MSK_LEN);
360 os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN);
361
362 return 1;
363 }
364
365
eap_pwd_element_coord_ok(const struct crypto_bignum * prime,const u8 * buf,size_t len)366 static int eap_pwd_element_coord_ok(const struct crypto_bignum *prime,
367 const u8 *buf, size_t len)
368 {
369 struct crypto_bignum *val;
370 int ok = 1;
371
372 val = crypto_bignum_init_set(buf, len);
373 if (!val || crypto_bignum_is_zero(val) ||
374 crypto_bignum_cmp(val, prime) >= 0)
375 ok = 0;
376 crypto_bignum_deinit(val, 0);
377 return ok;
378 }
379
380
eap_pwd_get_element(EAP_PWD_group * group,const u8 * buf)381 struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group,
382 const u8 *buf)
383 {
384 struct crypto_ec_point *element;
385 const struct crypto_bignum *prime;
386 size_t prime_len;
387
388 prime = crypto_ec_get_prime(group->group);
389 prime_len = crypto_ec_prime_len(group->group);
390
391 /* RFC 5931, 2.8.5.2.2: 0 < x,y < p */
392 if (!eap_pwd_element_coord_ok(prime, buf, prime_len) ||
393 !eap_pwd_element_coord_ok(prime, buf + prime_len, prime_len)) {
394 wpa_printf(MSG_INFO, "EAP-pwd: Invalid coordinate in element");
395 return NULL;
396 }
397
398 element = crypto_ec_point_from_bin(group->group, buf);
399 if (!element) {
400 wpa_printf(MSG_INFO, "EAP-pwd: EC point from element failed");
401 return NULL;
402 }
403
404 /* RFC 5931, 2.8.5.2.2: on curve and not the point at infinity */
405 if (!crypto_ec_point_is_on_curve(group->group, element) ||
406 crypto_ec_point_is_at_infinity(group->group, element)) {
407 wpa_printf(MSG_INFO, "EAP-pwd: Invalid element");
408 goto fail;
409 }
410
411 out:
412 return element;
413 fail:
414 crypto_ec_point_deinit(element, 0);
415 element = NULL;
416 goto out;
417 }
418
419
eap_pwd_get_scalar(EAP_PWD_group * group,const u8 * buf)420 struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf)
421 {
422 struct crypto_bignum *scalar;
423 const struct crypto_bignum *order;
424 size_t order_len;
425
426 order = crypto_ec_get_order(group->group);
427 order_len = crypto_ec_order_len(group->group);
428
429 /* RFC 5931, 2.8.5.2: 1 < scalar < r */
430 scalar = crypto_bignum_init_set(buf, order_len);
431 if (!scalar || crypto_bignum_is_zero(scalar) ||
432 crypto_bignum_is_one(scalar) ||
433 crypto_bignum_cmp(scalar, order) >= 0) {
434 wpa_printf(MSG_INFO, "EAP-pwd: received scalar is invalid");
435 crypto_bignum_deinit(scalar, 0);
436 scalar = NULL;
437 }
438
439 return scalar;
440 }
441
442
eap_pwd_get_rand_mask(EAP_PWD_group * group,struct crypto_bignum * _rand,struct crypto_bignum * _mask,struct crypto_bignum * scalar)443 int eap_pwd_get_rand_mask(EAP_PWD_group *group, struct crypto_bignum *_rand,
444 struct crypto_bignum *_mask,
445 struct crypto_bignum *scalar)
446 {
447 return dragonfly_generate_scalar(crypto_ec_get_order(group->group),
448 _rand, _mask, scalar);
449 }
450