jpake.c revision 331638
1#include "jpake.h" 2 3#include <openssl/crypto.h> 4#include <openssl/sha.h> 5#include <openssl/err.h> 6#include <memory.h> 7#include <string.h> 8 9/* 10 * In the definition, (xa, xb, xc, xd) are Alice's (x1, x2, x3, x4) or 11 * Bob's (x3, x4, x1, x2). If you see what I mean. 12 */ 13 14typedef struct { 15 char *name; /* Must be unique */ 16 char *peer_name; 17 BIGNUM *p; 18 BIGNUM *g; 19 BIGNUM *q; 20 BIGNUM *gxc; /* Alice's g^{x3} or Bob's g^{x1} */ 21 BIGNUM *gxd; /* Alice's g^{x4} or Bob's g^{x2} */ 22} JPAKE_CTX_PUBLIC; 23 24struct JPAKE_CTX { 25 JPAKE_CTX_PUBLIC p; 26 BIGNUM *secret; /* The shared secret */ 27 BN_CTX *ctx; 28 BIGNUM *xa; /* Alice's x1 or Bob's x3 */ 29 BIGNUM *xb; /* Alice's x2 or Bob's x4 */ 30 BIGNUM *key; /* The calculated (shared) key */ 31}; 32 33static void JPAKE_ZKP_init(JPAKE_ZKP *zkp) 34{ 35 zkp->gr = BN_new(); 36 zkp->b = BN_new(); 37} 38 39static void JPAKE_ZKP_release(JPAKE_ZKP *zkp) 40{ 41 BN_free(zkp->b); 42 BN_free(zkp->gr); 43} 44 45/* Two birds with one stone - make the global name as expected */ 46#define JPAKE_STEP_PART_init JPAKE_STEP2_init 47#define JPAKE_STEP_PART_release JPAKE_STEP2_release 48 49void JPAKE_STEP_PART_init(JPAKE_STEP_PART *p) 50{ 51 p->gx = BN_new(); 52 JPAKE_ZKP_init(&p->zkpx); 53} 54 55void JPAKE_STEP_PART_release(JPAKE_STEP_PART *p) 56{ 57 JPAKE_ZKP_release(&p->zkpx); 58 BN_free(p->gx); 59} 60 61void JPAKE_STEP1_init(JPAKE_STEP1 *s1) 62{ 63 JPAKE_STEP_PART_init(&s1->p1); 64 JPAKE_STEP_PART_init(&s1->p2); 65} 66 67void JPAKE_STEP1_release(JPAKE_STEP1 *s1) 68{ 69 JPAKE_STEP_PART_release(&s1->p2); 70 JPAKE_STEP_PART_release(&s1->p1); 71} 72 73static void JPAKE_CTX_init(JPAKE_CTX *ctx, const char *name, 74 const char *peer_name, const BIGNUM *p, 75 const BIGNUM *g, const BIGNUM *q, 76 const BIGNUM *secret) 77{ 78 ctx->p.name = OPENSSL_strdup(name); 79 ctx->p.peer_name = OPENSSL_strdup(peer_name); 80 ctx->p.p = BN_dup(p); 81 ctx->p.g = BN_dup(g); 82 ctx->p.q = BN_dup(q); 83 ctx->secret = BN_dup(secret); 84 85 ctx->p.gxc = BN_new(); 86 ctx->p.gxd = BN_new(); 87 88 ctx->xa = BN_new(); 89 ctx->xb = BN_new(); 90 ctx->key = BN_new(); 91 ctx->ctx = BN_CTX_new(); 92} 93 94static void JPAKE_CTX_release(JPAKE_CTX *ctx) 95{ 96 BN_CTX_free(ctx->ctx); 97 BN_clear_free(ctx->key); 98 BN_clear_free(ctx->xb); 99 BN_clear_free(ctx->xa); 100 101 BN_free(ctx->p.gxd); 102 BN_free(ctx->p.gxc); 103 104 BN_clear_free(ctx->secret); 105 BN_free(ctx->p.q); 106 BN_free(ctx->p.g); 107 BN_free(ctx->p.p); 108 OPENSSL_free(ctx->p.peer_name); 109 OPENSSL_free(ctx->p.name); 110 111 memset(ctx, '\0', sizeof(*ctx)); 112} 113 114JPAKE_CTX *JPAKE_CTX_new(const char *name, const char *peer_name, 115 const BIGNUM *p, const BIGNUM *g, const BIGNUM *q, 116 const BIGNUM *secret) 117{ 118 JPAKE_CTX *ctx = OPENSSL_malloc(sizeof(*ctx)); 119 if (ctx == NULL) 120 return NULL; 121 122 JPAKE_CTX_init(ctx, name, peer_name, p, g, q, secret); 123 124 return ctx; 125} 126 127void JPAKE_CTX_free(JPAKE_CTX *ctx) 128{ 129 JPAKE_CTX_release(ctx); 130 OPENSSL_free(ctx); 131} 132 133static void hashlength(SHA_CTX *sha, size_t l) 134{ 135 unsigned char b[2]; 136 137 OPENSSL_assert(l <= 0xffff); 138 b[0] = l >> 8; 139 b[1] = l & 0xff; 140 SHA1_Update(sha, b, 2); 141} 142 143static void hashstring(SHA_CTX *sha, const char *string) 144{ 145 size_t l = strlen(string); 146 147 hashlength(sha, l); 148 SHA1_Update(sha, string, l); 149} 150 151static void hashbn(SHA_CTX *sha, const BIGNUM *bn) 152{ 153 size_t l = BN_num_bytes(bn); 154 unsigned char *bin = OPENSSL_malloc(l); 155 156 if (bin == NULL) 157 return; 158 hashlength(sha, l); 159 BN_bn2bin(bn, bin); 160 SHA1_Update(sha, bin, l); 161 OPENSSL_free(bin); 162} 163 164/* h=hash(g, g^r, g^x, name) */ 165static void zkp_hash(BIGNUM *h, const BIGNUM *zkpg, const JPAKE_STEP_PART *p, 166 const char *proof_name) 167{ 168 unsigned char md[SHA_DIGEST_LENGTH]; 169 SHA_CTX sha; 170 171 /* 172 * XXX: hash should not allow moving of the boundaries - Java code 173 * is flawed in this respect. Length encoding seems simplest. 174 */ 175 SHA1_Init(&sha); 176 hashbn(&sha, zkpg); 177 OPENSSL_assert(!BN_is_zero(p->zkpx.gr)); 178 hashbn(&sha, p->zkpx.gr); 179 hashbn(&sha, p->gx); 180 hashstring(&sha, proof_name); 181 SHA1_Final(md, &sha); 182 BN_bin2bn(md, SHA_DIGEST_LENGTH, h); 183} 184 185/* 186 * Prove knowledge of x 187 * Note that p->gx has already been calculated 188 */ 189static void generate_zkp(JPAKE_STEP_PART *p, const BIGNUM *x, 190 const BIGNUM *zkpg, JPAKE_CTX *ctx) 191{ 192 BIGNUM *r = BN_new(); 193 BIGNUM *h = BN_new(); 194 BIGNUM *t = BN_new(); 195 196 /*- 197 * r in [0,q) 198 * XXX: Java chooses r in [0, 2^160) - i.e. distribution not uniform 199 */ 200 BN_rand_range(r, ctx->p.q); 201 /* g^r */ 202 BN_mod_exp(p->zkpx.gr, zkpg, r, ctx->p.p, ctx->ctx); 203 204 /* h=hash... */ 205 zkp_hash(h, zkpg, p, ctx->p.name); 206 207 /* b = r - x*h */ 208 BN_mod_mul(t, x, h, ctx->p.q, ctx->ctx); 209 BN_mod_sub(p->zkpx.b, r, t, ctx->p.q, ctx->ctx); 210 211 /* cleanup */ 212 BN_free(t); 213 BN_free(h); 214 BN_free(r); 215} 216 217static int verify_zkp(const JPAKE_STEP_PART *p, const BIGNUM *zkpg, 218 JPAKE_CTX *ctx) 219{ 220 BIGNUM *h = BN_new(); 221 BIGNUM *t1 = BN_new(); 222 BIGNUM *t2 = BN_new(); 223 BIGNUM *t3 = BN_new(); 224 int ret = 0; 225 226 if (h == NULL || t1 == NULL || t2 == NULL || t3 == NULL) 227 goto end; 228 229 zkp_hash(h, zkpg, p, ctx->p.peer_name); 230 231 /* t1 = g^b */ 232 BN_mod_exp(t1, zkpg, p->zkpx.b, ctx->p.p, ctx->ctx); 233 /* t2 = (g^x)^h = g^{hx} */ 234 BN_mod_exp(t2, p->gx, h, ctx->p.p, ctx->ctx); 235 /* t3 = t1 * t2 = g^{hx} * g^b = g^{hx+b} = g^r (allegedly) */ 236 BN_mod_mul(t3, t1, t2, ctx->p.p, ctx->ctx); 237 238 /* verify t3 == g^r */ 239 if (BN_cmp(t3, p->zkpx.gr) == 0) 240 ret = 1; 241 else 242 JPAKEerr(JPAKE_F_VERIFY_ZKP, JPAKE_R_ZKP_VERIFY_FAILED); 243 244end: 245 /* cleanup */ 246 BN_free(t3); 247 BN_free(t2); 248 BN_free(t1); 249 BN_free(h); 250 251 return ret; 252} 253 254static void generate_step_part(JPAKE_STEP_PART *p, const BIGNUM *x, 255 const BIGNUM *g, JPAKE_CTX *ctx) 256{ 257 BN_mod_exp(p->gx, g, x, ctx->p.p, ctx->ctx); 258 generate_zkp(p, x, g, ctx); 259} 260 261/* Generate each party's random numbers. xa is in [0, q), xb is in [1, q). */ 262static void genrand(JPAKE_CTX *ctx) 263{ 264 BIGNUM *qm1; 265 266 /* xa in [0, q) */ 267 BN_rand_range(ctx->xa, ctx->p.q); 268 269 /* q-1 */ 270 qm1 = BN_new(); 271 BN_copy(qm1, ctx->p.q); 272 BN_sub_word(qm1, 1); 273 274 /* ... and xb in [0, q-1) */ 275 BN_rand_range(ctx->xb, qm1); 276 /* [1, q) */ 277 BN_add_word(ctx->xb, 1); 278 279 /* cleanup */ 280 BN_free(qm1); 281} 282 283int JPAKE_STEP1_generate(JPAKE_STEP1 *send, JPAKE_CTX *ctx) 284{ 285 genrand(ctx); 286 generate_step_part(&send->p1, ctx->xa, ctx->p.g, ctx); 287 generate_step_part(&send->p2, ctx->xb, ctx->p.g, ctx); 288 289 return 1; 290} 291 292/* g^x is a legal value */ 293static int is_legal(const BIGNUM *gx, const JPAKE_CTX *ctx) 294{ 295 BIGNUM *t; 296 int res; 297 298 if (BN_is_negative(gx) || BN_is_zero(gx) || BN_cmp(gx, ctx->p.p) >= 0) 299 return 0; 300 301 t = BN_new(); 302 BN_mod_exp(t, gx, ctx->p.q, ctx->p.p, ctx->ctx); 303 res = BN_is_one(t); 304 BN_free(t); 305 306 return res; 307} 308 309int JPAKE_STEP1_process(JPAKE_CTX *ctx, const JPAKE_STEP1 *received) 310{ 311 if (!is_legal(received->p1.gx, ctx)) { 312 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, 313 JPAKE_R_G_TO_THE_X3_IS_NOT_LEGAL); 314 return 0; 315 } 316 317 if (!is_legal(received->p2.gx, ctx)) { 318 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, 319 JPAKE_R_G_TO_THE_X4_IS_NOT_LEGAL); 320 return 0; 321 } 322 323 /* verify their ZKP(xc) */ 324 if (!verify_zkp(&received->p1, ctx->p.g, ctx)) { 325 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_VERIFY_X3_FAILED); 326 return 0; 327 } 328 329 /* verify their ZKP(xd) */ 330 if (!verify_zkp(&received->p2, ctx->p.g, ctx)) { 331 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_VERIFY_X4_FAILED); 332 return 0; 333 } 334 335 /* g^xd != 1 */ 336 if (BN_is_one(received->p2.gx)) { 337 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_G_TO_THE_X4_IS_ONE); 338 return 0; 339 } 340 341 /* Save the bits we need for later */ 342 BN_copy(ctx->p.gxc, received->p1.gx); 343 BN_copy(ctx->p.gxd, received->p2.gx); 344 345 return 1; 346} 347 348int JPAKE_STEP2_generate(JPAKE_STEP2 *send, JPAKE_CTX *ctx) 349{ 350 BIGNUM *t1 = BN_new(); 351 BIGNUM *t2 = BN_new(); 352 353 /*- 354 * X = g^{(xa + xc + xd) * xb * s} 355 * t1 = g^xa 356 */ 357 BN_mod_exp(t1, ctx->p.g, ctx->xa, ctx->p.p, ctx->ctx); 358 /* t2 = t1 * g^{xc} = g^{xa} * g^{xc} = g^{xa + xc} */ 359 BN_mod_mul(t2, t1, ctx->p.gxc, ctx->p.p, ctx->ctx); 360 /* t1 = t2 * g^{xd} = g^{xa + xc + xd} */ 361 BN_mod_mul(t1, t2, ctx->p.gxd, ctx->p.p, ctx->ctx); 362 /* t2 = xb * s */ 363 BN_mod_mul(t2, ctx->xb, ctx->secret, ctx->p.q, ctx->ctx); 364 365 /*- 366 * ZKP(xb * s) 367 * XXX: this is kinda funky, because we're using 368 * 369 * g' = g^{xa + xc + xd} 370 * 371 * as the generator, which means X is g'^{xb * s} 372 * X = t1^{t2} = t1^{xb * s} = g^{(xa + xc + xd) * xb * s} 373 */ 374 generate_step_part(send, t2, t1, ctx); 375 376 /* cleanup */ 377 BN_free(t1); 378 BN_free(t2); 379 380 return 1; 381} 382 383/* gx = g^{xc + xa + xb} * xd * s */ 384static int compute_key(JPAKE_CTX *ctx, const BIGNUM *gx) 385{ 386 BIGNUM *t1 = BN_new(); 387 BIGNUM *t2 = BN_new(); 388 BIGNUM *t3 = BN_new(); 389 390 /*- 391 * K = (gx/g^{xb * xd * s})^{xb} 392 * = (g^{(xc + xa + xb) * xd * s - xb * xd *s})^{xb} 393 * = (g^{(xa + xc) * xd * s})^{xb} 394 * = g^{(xa + xc) * xb * xd * s} 395 * [which is the same regardless of who calculates it] 396 */ 397 398 /* t1 = (g^{xd})^{xb} = g^{xb * xd} */ 399 BN_mod_exp(t1, ctx->p.gxd, ctx->xb, ctx->p.p, ctx->ctx); 400 /* t2 = -s = q-s */ 401 BN_sub(t2, ctx->p.q, ctx->secret); 402 /* t3 = t1^t2 = g^{-xb * xd * s} */ 403 BN_mod_exp(t3, t1, t2, ctx->p.p, ctx->ctx); 404 /* t1 = gx * t3 = X/g^{xb * xd * s} */ 405 BN_mod_mul(t1, gx, t3, ctx->p.p, ctx->ctx); 406 /* K = t1^{xb} */ 407 BN_mod_exp(ctx->key, t1, ctx->xb, ctx->p.p, ctx->ctx); 408 409 /* cleanup */ 410 BN_free(t3); 411 BN_free(t2); 412 BN_free(t1); 413 414 return 1; 415} 416 417int JPAKE_STEP2_process(JPAKE_CTX *ctx, const JPAKE_STEP2 *received) 418{ 419 BIGNUM *t1 = BN_new(); 420 BIGNUM *t2 = BN_new(); 421 int ret = 0; 422 423 /*- 424 * g' = g^{xc + xa + xb} [from our POV] 425 * t1 = xa + xb 426 */ 427 BN_mod_add(t1, ctx->xa, ctx->xb, ctx->p.q, ctx->ctx); 428 /* t2 = g^{t1} = g^{xa+xb} */ 429 BN_mod_exp(t2, ctx->p.g, t1, ctx->p.p, ctx->ctx); 430 /* t1 = g^{xc} * t2 = g^{xc + xa + xb} */ 431 BN_mod_mul(t1, ctx->p.gxc, t2, ctx->p.p, ctx->ctx); 432 433 if (verify_zkp(received, t1, ctx)) 434 ret = 1; 435 else 436 JPAKEerr(JPAKE_F_JPAKE_STEP2_PROCESS, JPAKE_R_VERIFY_B_FAILED); 437 438 compute_key(ctx, received->gx); 439 440 /* cleanup */ 441 BN_free(t2); 442 BN_free(t1); 443 444 return ret; 445} 446 447static void quickhashbn(unsigned char *md, const BIGNUM *bn) 448{ 449 SHA_CTX sha; 450 451 SHA1_Init(&sha); 452 hashbn(&sha, bn); 453 SHA1_Final(md, &sha); 454} 455 456void JPAKE_STEP3A_init(JPAKE_STEP3A *s3a) 457{ 458} 459 460int JPAKE_STEP3A_generate(JPAKE_STEP3A *send, JPAKE_CTX *ctx) 461{ 462 quickhashbn(send->hhk, ctx->key); 463 SHA1(send->hhk, sizeof(send->hhk), send->hhk); 464 465 return 1; 466} 467 468int JPAKE_STEP3A_process(JPAKE_CTX *ctx, const JPAKE_STEP3A *received) 469{ 470 unsigned char hhk[SHA_DIGEST_LENGTH]; 471 472 quickhashbn(hhk, ctx->key); 473 SHA1(hhk, sizeof(hhk), hhk); 474 if (memcmp(hhk, received->hhk, sizeof(hhk))) { 475 JPAKEerr(JPAKE_F_JPAKE_STEP3A_PROCESS, 476 JPAKE_R_HASH_OF_HASH_OF_KEY_MISMATCH); 477 return 0; 478 } 479 return 1; 480} 481 482void JPAKE_STEP3A_release(JPAKE_STEP3A *s3a) 483{ 484} 485 486void JPAKE_STEP3B_init(JPAKE_STEP3B *s3b) 487{ 488} 489 490int JPAKE_STEP3B_generate(JPAKE_STEP3B *send, JPAKE_CTX *ctx) 491{ 492 quickhashbn(send->hk, ctx->key); 493 494 return 1; 495} 496 497int JPAKE_STEP3B_process(JPAKE_CTX *ctx, const JPAKE_STEP3B *received) 498{ 499 unsigned char hk[SHA_DIGEST_LENGTH]; 500 501 quickhashbn(hk, ctx->key); 502 if (memcmp(hk, received->hk, sizeof(hk))) { 503 JPAKEerr(JPAKE_F_JPAKE_STEP3B_PROCESS, JPAKE_R_HASH_OF_KEY_MISMATCH); 504 return 0; 505 } 506 return 1; 507} 508 509void JPAKE_STEP3B_release(JPAKE_STEP3B *s3b) 510{ 511} 512 513const BIGNUM *JPAKE_get_shared_key(JPAKE_CTX *ctx) 514{ 515 return ctx->key; 516} 517