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); 119 120 JPAKE_CTX_init(ctx, name, peer_name, p, g, q, secret); 121 122 return ctx; 123} 124 125void JPAKE_CTX_free(JPAKE_CTX *ctx) 126{ 127 JPAKE_CTX_release(ctx); 128 OPENSSL_free(ctx); 129} 130 131static void hashlength(SHA_CTX *sha, size_t l) 132{ 133 unsigned char b[2]; 134 135 OPENSSL_assert(l <= 0xffff); 136 b[0] = l >> 8; 137 b[1] = l & 0xff; 138 SHA1_Update(sha, b, 2); 139} 140 141static void hashstring(SHA_CTX *sha, const char *string) 142{ 143 size_t l = strlen(string); 144 145 hashlength(sha, l); 146 SHA1_Update(sha, string, l); 147} 148 149static void hashbn(SHA_CTX *sha, const BIGNUM *bn) 150{ 151 size_t l = BN_num_bytes(bn); 152 unsigned char *bin = OPENSSL_malloc(l); 153 154 hashlength(sha, l); 155 BN_bn2bin(bn, bin); 156 SHA1_Update(sha, bin, l); 157 OPENSSL_free(bin); 158} 159 160/* h=hash(g, g^r, g^x, name) */ 161static void zkp_hash(BIGNUM *h, const BIGNUM *zkpg, const JPAKE_STEP_PART *p, 162 const char *proof_name) 163{ 164 unsigned char md[SHA_DIGEST_LENGTH]; 165 SHA_CTX sha; 166 167 /* 168 * XXX: hash should not allow moving of the boundaries - Java code 169 * is flawed in this respect. Length encoding seems simplest. 170 */ 171 SHA1_Init(&sha); 172 hashbn(&sha, zkpg); 173 OPENSSL_assert(!BN_is_zero(p->zkpx.gr)); 174 hashbn(&sha, p->zkpx.gr); 175 hashbn(&sha, p->gx); 176 hashstring(&sha, proof_name); 177 SHA1_Final(md, &sha); 178 BN_bin2bn(md, SHA_DIGEST_LENGTH, h); 179} 180 181/* 182 * Prove knowledge of x 183 * Note that p->gx has already been calculated 184 */ 185static void generate_zkp(JPAKE_STEP_PART *p, const BIGNUM *x, 186 const BIGNUM *zkpg, JPAKE_CTX *ctx) 187{ 188 BIGNUM *r = BN_new(); 189 BIGNUM *h = BN_new(); 190 BIGNUM *t = BN_new(); 191 192 /*- 193 * r in [0,q) 194 * XXX: Java chooses r in [0, 2^160) - i.e. distribution not uniform 195 */ 196 BN_rand_range(r, ctx->p.q); 197 /* g^r */ 198 BN_mod_exp(p->zkpx.gr, zkpg, r, ctx->p.p, ctx->ctx); 199 200 /* h=hash... */ 201 zkp_hash(h, zkpg, p, ctx->p.name); 202 203 /* b = r - x*h */ 204 BN_mod_mul(t, x, h, ctx->p.q, ctx->ctx); 205 BN_mod_sub(p->zkpx.b, r, t, ctx->p.q, ctx->ctx); 206 207 /* cleanup */ 208 BN_free(t); 209 BN_free(h); 210 BN_free(r); 211} 212 213static int verify_zkp(const JPAKE_STEP_PART *p, const BIGNUM *zkpg, 214 JPAKE_CTX *ctx) 215{ 216 BIGNUM *h = BN_new(); 217 BIGNUM *t1 = BN_new(); 218 BIGNUM *t2 = BN_new(); 219 BIGNUM *t3 = BN_new(); 220 int ret = 0; 221 222 if (h == NULL || t1 == NULL || t2 == NULL || t3 == NULL) 223 goto end; 224 225 zkp_hash(h, zkpg, p, ctx->p.peer_name); 226 227 /* t1 = g^b */ 228 BN_mod_exp(t1, zkpg, p->zkpx.b, ctx->p.p, ctx->ctx); 229 /* t2 = (g^x)^h = g^{hx} */ 230 BN_mod_exp(t2, p->gx, h, ctx->p.p, ctx->ctx); 231 /* t3 = t1 * t2 = g^{hx} * g^b = g^{hx+b} = g^r (allegedly) */ 232 BN_mod_mul(t3, t1, t2, ctx->p.p, ctx->ctx); 233 234 /* verify t3 == g^r */ 235 if (BN_cmp(t3, p->zkpx.gr) == 0) 236 ret = 1; 237 else 238 JPAKEerr(JPAKE_F_VERIFY_ZKP, JPAKE_R_ZKP_VERIFY_FAILED); 239 240end: 241 /* cleanup */ 242 BN_free(t3); 243 BN_free(t2); 244 BN_free(t1); 245 BN_free(h); 246 247 return ret; 248} 249 250static void generate_step_part(JPAKE_STEP_PART *p, const BIGNUM *x, 251 const BIGNUM *g, JPAKE_CTX *ctx) 252{ 253 BN_mod_exp(p->gx, g, x, ctx->p.p, ctx->ctx); 254 generate_zkp(p, x, g, ctx); 255} 256 257/* Generate each party's random numbers. xa is in [0, q), xb is in [1, q). */ 258static void genrand(JPAKE_CTX *ctx) 259{ 260 BIGNUM *qm1; 261 262 /* xa in [0, q) */ 263 BN_rand_range(ctx->xa, ctx->p.q); 264 265 /* q-1 */ 266 qm1 = BN_new(); 267 BN_copy(qm1, ctx->p.q); 268 BN_sub_word(qm1, 1); 269 270 /* ... and xb in [0, q-1) */ 271 BN_rand_range(ctx->xb, qm1); 272 /* [1, q) */ 273 BN_add_word(ctx->xb, 1); 274 275 /* cleanup */ 276 BN_free(qm1); 277} 278 279int JPAKE_STEP1_generate(JPAKE_STEP1 *send, JPAKE_CTX *ctx) 280{ 281 genrand(ctx); 282 generate_step_part(&send->p1, ctx->xa, ctx->p.g, ctx); 283 generate_step_part(&send->p2, ctx->xb, ctx->p.g, ctx); 284 285 return 1; 286} 287 288/* g^x is a legal value */ 289static int is_legal(const BIGNUM *gx, const JPAKE_CTX *ctx) 290{ 291 BIGNUM *t; 292 int res; 293 294 if (BN_is_negative(gx) || BN_is_zero(gx) || BN_cmp(gx, ctx->p.p) >= 0) 295 return 0; 296 297 t = BN_new(); 298 BN_mod_exp(t, gx, ctx->p.q, ctx->p.p, ctx->ctx); 299 res = BN_is_one(t); 300 BN_free(t); 301 302 return res; 303} 304 305int JPAKE_STEP1_process(JPAKE_CTX *ctx, const JPAKE_STEP1 *received) 306{ 307 if (!is_legal(received->p1.gx, ctx)) { 308 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, 309 JPAKE_R_G_TO_THE_X3_IS_NOT_LEGAL); 310 return 0; 311 } 312 313 if (!is_legal(received->p2.gx, ctx)) { 314 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, 315 JPAKE_R_G_TO_THE_X4_IS_NOT_LEGAL); 316 return 0; 317 } 318 319 /* verify their ZKP(xc) */ 320 if (!verify_zkp(&received->p1, ctx->p.g, ctx)) { 321 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_VERIFY_X3_FAILED); 322 return 0; 323 } 324 325 /* verify their ZKP(xd) */ 326 if (!verify_zkp(&received->p2, ctx->p.g, ctx)) { 327 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_VERIFY_X4_FAILED); 328 return 0; 329 } 330 331 /* g^xd != 1 */ 332 if (BN_is_one(received->p2.gx)) { 333 JPAKEerr(JPAKE_F_JPAKE_STEP1_PROCESS, JPAKE_R_G_TO_THE_X4_IS_ONE); 334 return 0; 335 } 336 337 /* Save the bits we need for later */ 338 BN_copy(ctx->p.gxc, received->p1.gx); 339 BN_copy(ctx->p.gxd, received->p2.gx); 340 341 return 1; 342} 343 344int JPAKE_STEP2_generate(JPAKE_STEP2 *send, JPAKE_CTX *ctx) 345{ 346 BIGNUM *t1 = BN_new(); 347 BIGNUM *t2 = BN_new(); 348 349 /*- 350 * X = g^{(xa + xc + xd) * xb * s} 351 * t1 = g^xa 352 */ 353 BN_mod_exp(t1, ctx->p.g, ctx->xa, ctx->p.p, ctx->ctx); 354 /* t2 = t1 * g^{xc} = g^{xa} * g^{xc} = g^{xa + xc} */ 355 BN_mod_mul(t2, t1, ctx->p.gxc, ctx->p.p, ctx->ctx); 356 /* t1 = t2 * g^{xd} = g^{xa + xc + xd} */ 357 BN_mod_mul(t1, t2, ctx->p.gxd, ctx->p.p, ctx->ctx); 358 /* t2 = xb * s */ 359 BN_mod_mul(t2, ctx->xb, ctx->secret, ctx->p.q, ctx->ctx); 360 361 /*- 362 * ZKP(xb * s) 363 * XXX: this is kinda funky, because we're using 364 * 365 * g' = g^{xa + xc + xd} 366 * 367 * as the generator, which means X is g'^{xb * s} 368 * X = t1^{t2} = t1^{xb * s} = g^{(xa + xc + xd) * xb * s} 369 */ 370 generate_step_part(send, t2, t1, ctx); 371 372 /* cleanup */ 373 BN_free(t1); 374 BN_free(t2); 375 376 return 1; 377} 378 379/* gx = g^{xc + xa + xb} * xd * s */ 380static int compute_key(JPAKE_CTX *ctx, const BIGNUM *gx) 381{ 382 BIGNUM *t1 = BN_new(); 383 BIGNUM *t2 = BN_new(); 384 BIGNUM *t3 = BN_new(); 385 386 /*- 387 * K = (gx/g^{xb * xd * s})^{xb} 388 * = (g^{(xc + xa + xb) * xd * s - xb * xd *s})^{xb} 389 * = (g^{(xa + xc) * xd * s})^{xb} 390 * = g^{(xa + xc) * xb * xd * s} 391 * [which is the same regardless of who calculates it] 392 */ 393 394 /* t1 = (g^{xd})^{xb} = g^{xb * xd} */ 395 BN_mod_exp(t1, ctx->p.gxd, ctx->xb, ctx->p.p, ctx->ctx); 396 /* t2 = -s = q-s */ 397 BN_sub(t2, ctx->p.q, ctx->secret); 398 /* t3 = t1^t2 = g^{-xb * xd * s} */ 399 BN_mod_exp(t3, t1, t2, ctx->p.p, ctx->ctx); 400 /* t1 = gx * t3 = X/g^{xb * xd * s} */ 401 BN_mod_mul(t1, gx, t3, ctx->p.p, ctx->ctx); 402 /* K = t1^{xb} */ 403 BN_mod_exp(ctx->key, t1, ctx->xb, ctx->p.p, ctx->ctx); 404 405 /* cleanup */ 406 BN_free(t3); 407 BN_free(t2); 408 BN_free(t1); 409 410 return 1; 411} 412 413int JPAKE_STEP2_process(JPAKE_CTX *ctx, const JPAKE_STEP2 *received) 414{ 415 BIGNUM *t1 = BN_new(); 416 BIGNUM *t2 = BN_new(); 417 int ret = 0; 418 419 /*- 420 * g' = g^{xc + xa + xb} [from our POV] 421 * t1 = xa + xb 422 */ 423 BN_mod_add(t1, ctx->xa, ctx->xb, ctx->p.q, ctx->ctx); 424 /* t2 = g^{t1} = g^{xa+xb} */ 425 BN_mod_exp(t2, ctx->p.g, t1, ctx->p.p, ctx->ctx); 426 /* t1 = g^{xc} * t2 = g^{xc + xa + xb} */ 427 BN_mod_mul(t1, ctx->p.gxc, t2, ctx->p.p, ctx->ctx); 428 429 if (verify_zkp(received, t1, ctx)) 430 ret = 1; 431 else 432 JPAKEerr(JPAKE_F_JPAKE_STEP2_PROCESS, JPAKE_R_VERIFY_B_FAILED); 433 434 compute_key(ctx, received->gx); 435 436 /* cleanup */ 437 BN_free(t2); 438 BN_free(t1); 439 440 return ret; 441} 442 443static void quickhashbn(unsigned char *md, const BIGNUM *bn) 444{ 445 SHA_CTX sha; 446 447 SHA1_Init(&sha); 448 hashbn(&sha, bn); 449 SHA1_Final(md, &sha); 450} 451 452void JPAKE_STEP3A_init(JPAKE_STEP3A *s3a) 453{ 454} 455 456int JPAKE_STEP3A_generate(JPAKE_STEP3A *send, JPAKE_CTX *ctx) 457{ 458 quickhashbn(send->hhk, ctx->key); 459 SHA1(send->hhk, sizeof send->hhk, send->hhk); 460 461 return 1; 462} 463 464int JPAKE_STEP3A_process(JPAKE_CTX *ctx, const JPAKE_STEP3A *received) 465{ 466 unsigned char hhk[SHA_DIGEST_LENGTH]; 467 468 quickhashbn(hhk, ctx->key); 469 SHA1(hhk, sizeof hhk, hhk); 470 if (memcmp(hhk, received->hhk, sizeof hhk)) { 471 JPAKEerr(JPAKE_F_JPAKE_STEP3A_PROCESS, 472 JPAKE_R_HASH_OF_HASH_OF_KEY_MISMATCH); 473 return 0; 474 } 475 return 1; 476} 477 478void JPAKE_STEP3A_release(JPAKE_STEP3A *s3a) 479{ 480} 481 482void JPAKE_STEP3B_init(JPAKE_STEP3B *s3b) 483{ 484} 485 486int JPAKE_STEP3B_generate(JPAKE_STEP3B *send, JPAKE_CTX *ctx) 487{ 488 quickhashbn(send->hk, ctx->key); 489 490 return 1; 491} 492 493int JPAKE_STEP3B_process(JPAKE_CTX *ctx, const JPAKE_STEP3B *received) 494{ 495 unsigned char hk[SHA_DIGEST_LENGTH]; 496 497 quickhashbn(hk, ctx->key); 498 if (memcmp(hk, received->hk, sizeof hk)) { 499 JPAKEerr(JPAKE_F_JPAKE_STEP3B_PROCESS, JPAKE_R_HASH_OF_KEY_MISMATCH); 500 return 0; 501 } 502 return 1; 503} 504 505void JPAKE_STEP3B_release(JPAKE_STEP3B *s3b) 506{ 507} 508 509const BIGNUM *JPAKE_get_shared_key(JPAKE_CTX *ctx) 510{ 511 return ctx->key; 512} 513