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 u8 x_y[2 * MAX_ECC_PRIME_LEN];
131 struct crypto_bignum *tmp2 = NULL, *y = NULL;
132 struct crypto_hash *hash;
133 unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr;
134 int ret = 0, res;
135 u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_*
136 * mask */
137 size_t primebytelen = 0, primebitlen;
138 struct crypto_bignum *x_candidate = NULL;
139 const struct crypto_bignum *prime;
140 u8 found_ctr = 0, is_odd = 0;
141 int cmp_prime;
142 unsigned int in_range;
143 unsigned int is_eq;
144
145 if (grp->pwe)
146 return -1;
147
148 os_memset(x_bin, 0, sizeof(x_bin));
149
150 prime = crypto_ec_get_prime(grp->group);
151 primebitlen = crypto_ec_prime_len_bits(grp->group);
152 primebytelen = crypto_ec_prime_len(grp->group);
153 if (crypto_bignum_to_bin(prime, prime_bin, sizeof(prime_bin),
154 primebytelen) < 0)
155 return -1;
156
157 if ((prfbuf = os_malloc(primebytelen)) == NULL) {
158 wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf "
159 "buffer");
160 goto fail;
161 }
162
163 /* get a random quadratic residue and nonresidue */
164 if (dragonfly_get_random_qr_qnr(prime, &qr, &qnr) < 0 ||
165 crypto_bignum_to_bin(qr, qr_bin, sizeof(qr_bin),
166 primebytelen) < 0 ||
167 crypto_bignum_to_bin(qnr, qnr_bin, sizeof(qnr_bin),
168 primebytelen) < 0)
169 goto fail;
170
171 os_memset(prfbuf, 0, primebytelen);
172 ctr = 0;
173
174 /*
175 * Run through the hunting-and-pecking loop 40 times to mask the time
176 * necessary to find PWE. The odds of PWE not being found in 40 loops is
177 * roughly 1 in 1 trillion.
178 */
179 while (ctr < 40) {
180 ctr++;
181
182 /*
183 * compute counter-mode password value and stretch to prime
184 * pwd-seed = H(token | peer-id | server-id | password |
185 * counter)
186 */
187 hash = eap_pwd_h_init();
188 if (hash == NULL)
189 goto fail;
190 eap_pwd_h_update(hash, token, sizeof(u32));
191 eap_pwd_h_update(hash, id_peer, id_peer_len);
192 eap_pwd_h_update(hash, id_server, id_server_len);
193 eap_pwd_h_update(hash, password, password_len);
194 eap_pwd_h_update(hash, &ctr, sizeof(ctr));
195 eap_pwd_h_final(hash, pwe_digest);
196
197 is_odd = const_time_select_u8(
198 found, is_odd, pwe_digest[SHA256_MAC_LEN - 1] & 0x01);
199 if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN,
200 (u8 *) "EAP-pwd Hunting And Pecking",
201 os_strlen("EAP-pwd Hunting And Pecking"),
202 prfbuf, primebitlen) < 0)
203 goto fail;
204 if (primebitlen % 8)
205 buf_shift_right(prfbuf, primebytelen,
206 8 - primebitlen % 8);
207 cmp_prime = const_time_memcmp(prfbuf, prime_bin, primebytelen);
208 /* Create a const_time mask for selection based on prf result
209 * being smaller than prime. */
210 in_range = const_time_fill_msb((unsigned int) cmp_prime);
211 /* The algorithm description would skip the next steps if
212 * cmp_prime >= 0, but go through them regardless to minimize
213 * externally observable differences in behavior. */
214
215 crypto_bignum_deinit(x_candidate, 1);
216 x_candidate = crypto_bignum_init_set(prfbuf, primebytelen);
217 if (!x_candidate) {
218 wpa_printf(MSG_INFO,
219 "EAP-pwd: unable to create x_candidate");
220 goto fail;
221 }
222
223 wpa_hexdump_key(MSG_DEBUG, "EAP-pwd: x_candidate",
224 prfbuf, primebytelen);
225 const_time_select_bin(found, x_bin, prfbuf, primebytelen,
226 x_bin);
227
228 /*
229 * compute y^2 using the equation of the curve
230 *
231 * y^2 = x^3 + ax + b
232 */
233 crypto_bignum_deinit(tmp2, 1);
234 tmp2 = crypto_ec_point_compute_y_sqr(grp->group, x_candidate);
235 if (!tmp2)
236 goto fail;
237
238 res = dragonfly_is_quadratic_residue_blind(grp->group, qr_bin,
239 qnr_bin, tmp2);
240 if (res < 0)
241 goto fail;
242 found_ctr = const_time_select_u8(found, found_ctr, ctr);
243 /* found is 0 or 0xff here and res is 0 or 1. Bitwise OR of them
244 * (with res converted to 0/0xff and masked with prf being below
245 * prime) handles this in constant time.
246 */
247 found |= (res & in_range) * 0xff;
248 }
249 if (found == 0) {
250 wpa_printf(MSG_INFO,
251 "EAP-pwd: unable to find random point on curve for group %d, something's fishy",
252 num);
253 goto fail;
254 }
255
256 /*
257 * We know x_candidate is a quadratic residue so set it here.
258 */
259 crypto_bignum_deinit(x_candidate, 1);
260 x_candidate = crypto_bignum_init_set(x_bin, primebytelen);
261 if (!x_candidate)
262 goto fail;
263
264 /* y = sqrt(x^3 + ax + b) mod p
265 * if LSB(y) == LSB(pwd-seed): PWE = (x, y)
266 * else: PWE = (x, p - y)
267 *
268 * Calculate y and the two possible values for PWE and after that,
269 * use constant time selection to copy the correct alternative.
270 */
271 y = crypto_ec_point_compute_y_sqr(grp->group, x_candidate);
272 if (!y ||
273 dragonfly_sqrt(grp->group, y, y) < 0 ||
274 crypto_bignum_to_bin(y, x_y, MAX_ECC_PRIME_LEN, primebytelen) < 0 ||
275 crypto_bignum_sub(prime, y, y) < 0 ||
276 crypto_bignum_to_bin(y, x_y + MAX_ECC_PRIME_LEN,
277 MAX_ECC_PRIME_LEN, primebytelen) < 0) {
278 wpa_printf(MSG_DEBUG, "SAE: Could not solve y");
279 goto fail;
280 }
281
282 /* Constant time selection of the y coordinate from the two
283 * options */
284 is_eq = const_time_eq(is_odd, x_y[primebytelen - 1] & 0x01);
285 const_time_select_bin(is_eq, x_y, x_y + MAX_ECC_PRIME_LEN,
286 primebytelen, x_y + primebytelen);
287 os_memcpy(x_y, x_bin, primebytelen);
288 wpa_hexdump_key(MSG_DEBUG, "EAP-pwd: PWE", x_y, 2 * primebytelen);
289 grp->pwe = crypto_ec_point_from_bin(grp->group, x_y);
290 if (!grp->pwe) {
291 wpa_printf(MSG_DEBUG, "EAP-pwd: Could not generate PWE");
292 goto fail;
293 }
294
295 /*
296 * If there's a solution to the equation then the point must be on the
297 * curve so why check again explicitly? OpenSSL code says this is
298 * required by X9.62. We're not X9.62 but it can't hurt just to be sure.
299 */
300 if (!crypto_ec_point_is_on_curve(grp->group, grp->pwe)) {
301 wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve");
302 goto fail;
303 }
304
305 wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %02d tries", found_ctr);
306
307 if (0) {
308 fail:
309 crypto_ec_point_deinit(grp->pwe, 1);
310 grp->pwe = NULL;
311 ret = 1;
312 }
313 /* cleanliness and order.... */
314 crypto_bignum_deinit(x_candidate, 1);
315 crypto_bignum_deinit(tmp2, 1);
316 crypto_bignum_deinit(y, 1);
317 crypto_bignum_deinit(qr, 1);
318 crypto_bignum_deinit(qnr, 1);
319 bin_clear_free(prfbuf, primebytelen);
320 os_memset(qr_bin, 0, sizeof(qr_bin));
321 os_memset(qnr_bin, 0, sizeof(qnr_bin));
322 os_memset(qr_or_qnr_bin, 0, sizeof(qr_or_qnr_bin));
323 os_memset(pwe_digest, 0, sizeof(pwe_digest));
324 forced_memzero(x_y, sizeof(x_y));
325
326 return ret;
327 }
328
329
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)330 int compute_keys(EAP_PWD_group *grp, const struct crypto_bignum *k,
331 const struct crypto_bignum *peer_scalar,
332 const struct crypto_bignum *server_scalar,
333 const u8 *confirm_peer, const u8 *confirm_server,
334 const u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id)
335 {
336 struct crypto_hash *hash;
337 u8 mk[SHA256_MAC_LEN], *cruft;
338 u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN];
339 size_t prime_len, order_len;
340
341 prime_len = crypto_ec_prime_len(grp->group);
342 order_len = crypto_ec_order_len(grp->group);
343
344 cruft = os_malloc(prime_len);
345 if (!cruft)
346 return -1;
347
348 /*
349 * first compute the session-id = TypeCode | H(ciphersuite | scal_p |
350 * scal_s)
351 */
352 session_id[0] = EAP_TYPE_PWD;
353 hash = eap_pwd_h_init();
354 if (hash == NULL) {
355 os_free(cruft);
356 return -1;
357 }
358 eap_pwd_h_update(hash, (const u8 *) ciphersuite, sizeof(u32));
359 crypto_bignum_to_bin(peer_scalar, cruft, order_len, order_len);
360 eap_pwd_h_update(hash, cruft, order_len);
361 crypto_bignum_to_bin(server_scalar, cruft, order_len, order_len);
362 eap_pwd_h_update(hash, cruft, order_len);
363 eap_pwd_h_final(hash, &session_id[1]);
364
365 /* then compute MK = H(k | confirm-peer | confirm-server) */
366 hash = eap_pwd_h_init();
367 if (hash == NULL) {
368 os_free(cruft);
369 return -1;
370 }
371 crypto_bignum_to_bin(k, cruft, prime_len, prime_len);
372 eap_pwd_h_update(hash, cruft, prime_len);
373 os_free(cruft);
374 eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN);
375 eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN);
376 eap_pwd_h_final(hash, mk);
377
378 /* stretch the mk with the session-id to get MSK | EMSK */
379 if (eap_pwd_kdf(mk, SHA256_MAC_LEN,
380 session_id, SHA256_MAC_LEN + 1,
381 msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) {
382 return -1;
383 }
384
385 os_memcpy(msk, msk_emsk, EAP_MSK_LEN);
386 os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN);
387
388 return 1;
389 }
390
391
eap_pwd_element_coord_ok(const struct crypto_bignum * prime,const u8 * buf,size_t len)392 static int eap_pwd_element_coord_ok(const struct crypto_bignum *prime,
393 const u8 *buf, size_t len)
394 {
395 struct crypto_bignum *val;
396 int ok = 1;
397
398 val = crypto_bignum_init_set(buf, len);
399 if (!val || crypto_bignum_is_zero(val) ||
400 crypto_bignum_cmp(val, prime) >= 0)
401 ok = 0;
402 crypto_bignum_deinit(val, 0);
403 return ok;
404 }
405
406
eap_pwd_get_element(EAP_PWD_group * group,const u8 * buf)407 struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group,
408 const u8 *buf)
409 {
410 struct crypto_ec_point *element;
411 const struct crypto_bignum *prime;
412 size_t prime_len;
413
414 prime = crypto_ec_get_prime(group->group);
415 prime_len = crypto_ec_prime_len(group->group);
416
417 /* RFC 5931, 2.8.5.2.2: 0 < x,y < p */
418 if (!eap_pwd_element_coord_ok(prime, buf, prime_len) ||
419 !eap_pwd_element_coord_ok(prime, buf + prime_len, prime_len)) {
420 wpa_printf(MSG_INFO, "EAP-pwd: Invalid coordinate in element");
421 return NULL;
422 }
423
424 element = crypto_ec_point_from_bin(group->group, buf);
425 if (!element) {
426 wpa_printf(MSG_INFO, "EAP-pwd: EC point from element failed");
427 return NULL;
428 }
429
430 /* RFC 5931, 2.8.5.2.2: on curve and not the point at infinity */
431 if (!crypto_ec_point_is_on_curve(group->group, element) ||
432 crypto_ec_point_is_at_infinity(group->group, element)) {
433 wpa_printf(MSG_INFO, "EAP-pwd: Invalid element");
434 goto fail;
435 }
436
437 out:
438 return element;
439 fail:
440 crypto_ec_point_deinit(element, 0);
441 element = NULL;
442 goto out;
443 }
444
445
eap_pwd_get_scalar(EAP_PWD_group * group,const u8 * buf)446 struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf)
447 {
448 struct crypto_bignum *scalar;
449 const struct crypto_bignum *order;
450 size_t order_len;
451
452 order = crypto_ec_get_order(group->group);
453 order_len = crypto_ec_order_len(group->group);
454
455 /* RFC 5931, 2.8.5.2: 1 < scalar < r */
456 scalar = crypto_bignum_init_set(buf, order_len);
457 if (!scalar || crypto_bignum_is_zero(scalar) ||
458 crypto_bignum_is_one(scalar) ||
459 crypto_bignum_cmp(scalar, order) >= 0) {
460 wpa_printf(MSG_INFO, "EAP-pwd: received scalar is invalid");
461 crypto_bignum_deinit(scalar, 0);
462 scalar = NULL;
463 }
464
465 return scalar;
466 }
467
468
eap_pwd_get_rand_mask(EAP_PWD_group * group,struct crypto_bignum * _rand,struct crypto_bignum * _mask,struct crypto_bignum * scalar)469 int eap_pwd_get_rand_mask(EAP_PWD_group *group, struct crypto_bignum *_rand,
470 struct crypto_bignum *_mask,
471 struct crypto_bignum *scalar)
472 {
473 return dragonfly_generate_scalar(crypto_ec_get_order(group->group),
474 _rand, _mask, scalar);
475 }
476