security/nss/lib/freebl/jpake.c

Wed, 31 Dec 2014 06:09:35 +0100

author
Michael Schloh von Bennewitz <michael@schloh.com>
date
Wed, 31 Dec 2014 06:09:35 +0100
changeset 0
6474c204b198
permissions
-rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

michael@0 1 /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0 2 * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0 3 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0 4
michael@0 5 #ifdef FREEBL_NO_DEPEND
michael@0 6 #include "stubs.h"
michael@0 7 #endif
michael@0 8
michael@0 9 #include "blapi.h"
michael@0 10 #include "secerr.h"
michael@0 11 #include "secitem.h"
michael@0 12 #include "secmpi.h"
michael@0 13
michael@0 14 /* Hash an item's length and then its value. Only items smaller than 2^16 bytes
michael@0 15 * are allowed. Lengths are hashed in network byte order. This is designed
michael@0 16 * to match the OpenSSL J-PAKE implementation.
michael@0 17 */
michael@0 18 static mp_err
michael@0 19 hashSECItem(HASHContext * hash, const SECItem * it)
michael@0 20 {
michael@0 21 unsigned char length[2];
michael@0 22
michael@0 23 if (it->len > 0xffff)
michael@0 24 return MP_BADARG;
michael@0 25
michael@0 26 length[0] = (unsigned char) (it->len >> 8);
michael@0 27 length[1] = (unsigned char) (it->len);
michael@0 28 hash->hashobj->update(hash->hash_context, length, 2);
michael@0 29 hash->hashobj->update(hash->hash_context, it->data, it->len);
michael@0 30 return MP_OKAY;
michael@0 31 }
michael@0 32
michael@0 33 /* Hash all public components of the signature, each prefixed with its
michael@0 34 length, and then convert the hash to an mp_int. */
michael@0 35 static mp_err
michael@0 36 hashPublicParams(HASH_HashType hashType, const SECItem * g,
michael@0 37 const SECItem * gv, const SECItem * gx,
michael@0 38 const SECItem * signerID, mp_int * h)
michael@0 39 {
michael@0 40 mp_err err;
michael@0 41 unsigned char hBuf[HASH_LENGTH_MAX];
michael@0 42 SECItem hItem;
michael@0 43 HASHContext hash;
michael@0 44
michael@0 45 hash.hashobj = HASH_GetRawHashObject(hashType);
michael@0 46 if (hash.hashobj == NULL || hash.hashobj->length > sizeof hBuf) {
michael@0 47 return MP_BADARG;
michael@0 48 }
michael@0 49 hash.hash_context = hash.hashobj->create();
michael@0 50 if (hash.hash_context == NULL) {
michael@0 51 return MP_MEM;
michael@0 52 }
michael@0 53
michael@0 54 hItem.data = hBuf;
michael@0 55 hItem.len = hash.hashobj->length;
michael@0 56
michael@0 57 hash.hashobj->begin(hash.hash_context);
michael@0 58 CHECK_MPI_OK( hashSECItem(&hash, g) );
michael@0 59 CHECK_MPI_OK( hashSECItem(&hash, gv) );
michael@0 60 CHECK_MPI_OK( hashSECItem(&hash, gx) );
michael@0 61 CHECK_MPI_OK( hashSECItem(&hash, signerID) );
michael@0 62 hash.hashobj->end(hash.hash_context, hItem.data, &hItem.len,
michael@0 63 sizeof hBuf);
michael@0 64 SECITEM_TO_MPINT(hItem, h);
michael@0 65
michael@0 66 cleanup:
michael@0 67 if (hash.hash_context != NULL) {
michael@0 68 hash.hashobj->destroy(hash.hash_context, PR_TRUE);
michael@0 69 }
michael@0 70
michael@0 71 return err;
michael@0 72 }
michael@0 73
michael@0 74 /* Generate a Schnorr signature for round 1 or round 2 */
michael@0 75 SECStatus
michael@0 76 JPAKE_Sign(PLArenaPool * arena, const PQGParams * pqg, HASH_HashType hashType,
michael@0 77 const SECItem * signerID, const SECItem * x,
michael@0 78 const SECItem * testRandom, const SECItem * gxIn, SECItem * gxOut,
michael@0 79 SECItem * gv, SECItem * r)
michael@0 80 {
michael@0 81 SECStatus rv = SECSuccess;
michael@0 82 mp_err err;
michael@0 83 mp_int p;
michael@0 84 mp_int q;
michael@0 85 mp_int g;
michael@0 86 mp_int X;
michael@0 87 mp_int GX;
michael@0 88 mp_int V;
michael@0 89 mp_int GV;
michael@0 90 mp_int h;
michael@0 91 mp_int tmp;
michael@0 92 mp_int R;
michael@0 93 SECItem v;
michael@0 94
michael@0 95 if (!arena ||
michael@0 96 !pqg || !pqg->prime.data || pqg->prime.len == 0 ||
michael@0 97 !pqg->subPrime.data || pqg->subPrime.len == 0 ||
michael@0 98 !pqg->base.data || pqg->base.len == 0 ||
michael@0 99 !signerID || !signerID->data || signerID->len == 0 ||
michael@0 100 !x || !x->data || x->len == 0 ||
michael@0 101 (testRandom && (!testRandom->data || testRandom->len == 0)) ||
michael@0 102 (gxIn == NULL && (!gxOut || gxOut->data != NULL)) ||
michael@0 103 (gxIn != NULL && (!gxIn->data || gxIn->len == 0 || gxOut != NULL)) ||
michael@0 104 !gv || gv->data != NULL ||
michael@0 105 !r || r->data != NULL) {
michael@0 106 PORT_SetError(SEC_ERROR_INVALID_ARGS);
michael@0 107 return SECFailure;
michael@0 108 }
michael@0 109
michael@0 110
michael@0 111 MP_DIGITS(&p) = 0;
michael@0 112 MP_DIGITS(&q) = 0;
michael@0 113 MP_DIGITS(&g) = 0;
michael@0 114 MP_DIGITS(&X) = 0;
michael@0 115 MP_DIGITS(&GX) = 0;
michael@0 116 MP_DIGITS(&V) = 0;
michael@0 117 MP_DIGITS(&GV) = 0;
michael@0 118 MP_DIGITS(&h) = 0;
michael@0 119 MP_DIGITS(&tmp) = 0;
michael@0 120 MP_DIGITS(&R) = 0;
michael@0 121
michael@0 122 CHECK_MPI_OK( mp_init(&p) );
michael@0 123 CHECK_MPI_OK( mp_init(&q) );
michael@0 124 CHECK_MPI_OK( mp_init(&g) );
michael@0 125 CHECK_MPI_OK( mp_init(&X) );
michael@0 126 CHECK_MPI_OK( mp_init(&GX) );
michael@0 127 CHECK_MPI_OK( mp_init(&V) );
michael@0 128 CHECK_MPI_OK( mp_init(&GV) );
michael@0 129 CHECK_MPI_OK( mp_init(&h) );
michael@0 130 CHECK_MPI_OK( mp_init(&tmp) );
michael@0 131 CHECK_MPI_OK( mp_init(&R) );
michael@0 132
michael@0 133 SECITEM_TO_MPINT(pqg->prime, &p);
michael@0 134 SECITEM_TO_MPINT(pqg->subPrime, &q);
michael@0 135 SECITEM_TO_MPINT(pqg->base, &g);
michael@0 136 SECITEM_TO_MPINT(*x, &X);
michael@0 137
michael@0 138 /* gx = g^x */
michael@0 139 if (gxIn == NULL) {
michael@0 140 CHECK_MPI_OK( mp_exptmod(&g, &X, &p, &GX) );
michael@0 141 MPINT_TO_SECITEM(&GX, gxOut, arena);
michael@0 142 gxIn = gxOut;
michael@0 143 } else {
michael@0 144 SECITEM_TO_MPINT(*gxIn, &GX);
michael@0 145 }
michael@0 146
michael@0 147 /* v is a random value in the q subgroup */
michael@0 148 if (testRandom == NULL) {
michael@0 149 v.data = NULL;
michael@0 150 rv = DSA_NewRandom(arena, &pqg->subPrime, &v);
michael@0 151 if (rv != SECSuccess) {
michael@0 152 goto cleanup;
michael@0 153 }
michael@0 154 } else {
michael@0 155 v.data = testRandom->data;
michael@0 156 v.len = testRandom->len;
michael@0 157 }
michael@0 158 SECITEM_TO_MPINT(v, &V);
michael@0 159
michael@0 160 /* gv = g^v (mod q), random v, 1 <= v < q */
michael@0 161 CHECK_MPI_OK( mp_exptmod(&g, &V, &p, &GV) );
michael@0 162 MPINT_TO_SECITEM(&GV, gv, arena);
michael@0 163
michael@0 164 /* h = H(g, gv, gx, signerID) */
michael@0 165 CHECK_MPI_OK( hashPublicParams(hashType, &pqg->base, gv, gxIn, signerID,
michael@0 166 &h) );
michael@0 167
michael@0 168 /* r = v - x*h (mod q) */
michael@0 169 CHECK_MPI_OK( mp_mulmod(&X, &h, &q, &tmp) );
michael@0 170 CHECK_MPI_OK( mp_submod(&V, &tmp, &q, &R) );
michael@0 171 MPINT_TO_SECITEM(&R, r, arena);
michael@0 172
michael@0 173 cleanup:
michael@0 174 mp_clear(&p);
michael@0 175 mp_clear(&q);
michael@0 176 mp_clear(&g);
michael@0 177 mp_clear(&X);
michael@0 178 mp_clear(&GX);
michael@0 179 mp_clear(&V);
michael@0 180 mp_clear(&GV);
michael@0 181 mp_clear(&h);
michael@0 182 mp_clear(&tmp);
michael@0 183 mp_clear(&R);
michael@0 184
michael@0 185 if (rv == SECSuccess && err != MP_OKAY) {
michael@0 186 MP_TO_SEC_ERROR(err);
michael@0 187 rv = SECFailure;
michael@0 188 }
michael@0 189 return rv;
michael@0 190 }
michael@0 191
michael@0 192 /* Verify a Schnorr signature generated by the peer in round 1 or round 2. */
michael@0 193 SECStatus
michael@0 194 JPAKE_Verify(PLArenaPool * arena, const PQGParams * pqg, HASH_HashType hashType,
michael@0 195 const SECItem * signerID, const SECItem * peerID,
michael@0 196 const SECItem * gx, const SECItem * gv, const SECItem * r)
michael@0 197 {
michael@0 198 SECStatus rv = SECSuccess;
michael@0 199 mp_err err;
michael@0 200 mp_int p;
michael@0 201 mp_int q;
michael@0 202 mp_int g;
michael@0 203 mp_int p_minus_1;
michael@0 204 mp_int GX;
michael@0 205 mp_int h;
michael@0 206 mp_int one;
michael@0 207 mp_int R;
michael@0 208 mp_int gr;
michael@0 209 mp_int gxh;
michael@0 210 mp_int gr_gxh;
michael@0 211 SECItem calculated;
michael@0 212
michael@0 213 if (!arena ||
michael@0 214 !pqg || !pqg->prime.data || pqg->prime.len == 0 ||
michael@0 215 !pqg->subPrime.data || pqg->subPrime.len == 0 ||
michael@0 216 !pqg->base.data || pqg->base.len == 0 ||
michael@0 217 !signerID || !signerID->data || signerID->len == 0 ||
michael@0 218 !peerID || !peerID->data || peerID->len == 0 ||
michael@0 219 !gx || !gx->data || gx->len == 0 ||
michael@0 220 !gv || !gv->data || gv->len == 0 ||
michael@0 221 !r || !r->data || r->len == 0 ||
michael@0 222 SECITEM_CompareItem(signerID, peerID) == SECEqual) {
michael@0 223 PORT_SetError(SEC_ERROR_INVALID_ARGS);
michael@0 224 return SECFailure;
michael@0 225 }
michael@0 226
michael@0 227 MP_DIGITS(&p) = 0;
michael@0 228 MP_DIGITS(&q) = 0;
michael@0 229 MP_DIGITS(&g) = 0;
michael@0 230 MP_DIGITS(&p_minus_1) = 0;
michael@0 231 MP_DIGITS(&GX) = 0;
michael@0 232 MP_DIGITS(&h) = 0;
michael@0 233 MP_DIGITS(&one) = 0;
michael@0 234 MP_DIGITS(&R) = 0;
michael@0 235 MP_DIGITS(&gr) = 0;
michael@0 236 MP_DIGITS(&gxh) = 0;
michael@0 237 MP_DIGITS(&gr_gxh) = 0;
michael@0 238 calculated.data = NULL;
michael@0 239
michael@0 240 CHECK_MPI_OK( mp_init(&p) );
michael@0 241 CHECK_MPI_OK( mp_init(&q) );
michael@0 242 CHECK_MPI_OK( mp_init(&g) );
michael@0 243 CHECK_MPI_OK( mp_init(&p_minus_1) );
michael@0 244 CHECK_MPI_OK( mp_init(&GX) );
michael@0 245 CHECK_MPI_OK( mp_init(&h) );
michael@0 246 CHECK_MPI_OK( mp_init(&one) );
michael@0 247 CHECK_MPI_OK( mp_init(&R) );
michael@0 248 CHECK_MPI_OK( mp_init(&gr) );
michael@0 249 CHECK_MPI_OK( mp_init(&gxh) );
michael@0 250 CHECK_MPI_OK( mp_init(&gr_gxh) );
michael@0 251
michael@0 252 SECITEM_TO_MPINT(pqg->prime, &p);
michael@0 253 SECITEM_TO_MPINT(pqg->subPrime, &q);
michael@0 254 SECITEM_TO_MPINT(pqg->base, &g);
michael@0 255 SECITEM_TO_MPINT(*gx, &GX);
michael@0 256 SECITEM_TO_MPINT(*r, &R);
michael@0 257
michael@0 258 CHECK_MPI_OK( mp_sub_d(&p, 1, &p_minus_1) );
michael@0 259 CHECK_MPI_OK( mp_exptmod(&GX, &q, &p, &one) );
michael@0 260 /* Check g^x is in [1, p-2], R is in [0, q-1], and (g^x)^q mod p == 1 */
michael@0 261 if (!(mp_cmp_z(&GX) > 0 &&
michael@0 262 mp_cmp(&GX, &p_minus_1) < 0 &&
michael@0 263 mp_cmp(&R, &q) < 0 &&
michael@0 264 mp_cmp_d(&one, 1) == 0)) {
michael@0 265 goto badSig;
michael@0 266 }
michael@0 267
michael@0 268 CHECK_MPI_OK( hashPublicParams(hashType, &pqg->base, gv, gx, peerID,
michael@0 269 &h) );
michael@0 270
michael@0 271 /* Calculate g^v = g^r * g^x^h */
michael@0 272 CHECK_MPI_OK( mp_exptmod(&g, &R, &p, &gr) );
michael@0 273 CHECK_MPI_OK( mp_exptmod(&GX, &h, &p, &gxh) );
michael@0 274 CHECK_MPI_OK( mp_mulmod(&gr, &gxh, &p, &gr_gxh) );
michael@0 275
michael@0 276 /* Compare calculated g^v to given g^v */
michael@0 277 MPINT_TO_SECITEM(&gr_gxh, &calculated, arena);
michael@0 278 if (calculated.len == gv->len &&
michael@0 279 NSS_SecureMemcmp(calculated.data, gv->data, calculated.len) == 0) {
michael@0 280 rv = SECSuccess;
michael@0 281 } else {
michael@0 282 badSig: PORT_SetError(SEC_ERROR_BAD_SIGNATURE);
michael@0 283 rv = SECFailure;
michael@0 284 }
michael@0 285
michael@0 286 cleanup:
michael@0 287 mp_clear(&p);
michael@0 288 mp_clear(&q);
michael@0 289 mp_clear(&g);
michael@0 290 mp_clear(&p_minus_1);
michael@0 291 mp_clear(&GX);
michael@0 292 mp_clear(&h);
michael@0 293 mp_clear(&one);
michael@0 294 mp_clear(&R);
michael@0 295 mp_clear(&gr);
michael@0 296 mp_clear(&gxh);
michael@0 297 mp_clear(&gr_gxh);
michael@0 298
michael@0 299 if (rv == SECSuccess && err != MP_OKAY) {
michael@0 300 MP_TO_SEC_ERROR(err);
michael@0 301 rv = SECFailure;
michael@0 302 }
michael@0 303 return rv;
michael@0 304 }
michael@0 305
michael@0 306 /* Calculate base = gx1*gx3*gx4 (mod p), i.e. g^(x1+x3+x4) (mod p) */
michael@0 307 static mp_err
michael@0 308 jpake_Round2Base(const SECItem * gx1, const SECItem * gx3,
michael@0 309 const SECItem * gx4, const mp_int * p, mp_int * base)
michael@0 310 {
michael@0 311 mp_err err;
michael@0 312 mp_int GX1;
michael@0 313 mp_int GX3;
michael@0 314 mp_int GX4;
michael@0 315 mp_int tmp;
michael@0 316
michael@0 317 MP_DIGITS(&GX1) = 0;
michael@0 318 MP_DIGITS(&GX3) = 0;
michael@0 319 MP_DIGITS(&GX4) = 0;
michael@0 320 MP_DIGITS(&tmp) = 0;
michael@0 321
michael@0 322 CHECK_MPI_OK( mp_init(&GX1) );
michael@0 323 CHECK_MPI_OK( mp_init(&GX3) );
michael@0 324 CHECK_MPI_OK( mp_init(&GX4) );
michael@0 325 CHECK_MPI_OK( mp_init(&tmp) );
michael@0 326
michael@0 327 SECITEM_TO_MPINT(*gx1, &GX1);
michael@0 328 SECITEM_TO_MPINT(*gx3, &GX3);
michael@0 329 SECITEM_TO_MPINT(*gx4, &GX4);
michael@0 330
michael@0 331 /* In round 2, the peer/attacker sends us g^x3 and g^x4 and the protocol
michael@0 332 requires that these values are distinct. */
michael@0 333 if (mp_cmp(&GX3, &GX4) == 0) {
michael@0 334 return MP_BADARG;
michael@0 335 }
michael@0 336
michael@0 337 CHECK_MPI_OK( mp_mul(&GX1, &GX3, &tmp) );
michael@0 338 CHECK_MPI_OK( mp_mul(&tmp, &GX4, &tmp) );
michael@0 339 CHECK_MPI_OK( mp_mod(&tmp, p, base) );
michael@0 340
michael@0 341 cleanup:
michael@0 342 mp_clear(&GX1);
michael@0 343 mp_clear(&GX3);
michael@0 344 mp_clear(&GX4);
michael@0 345 mp_clear(&tmp);
michael@0 346 return err;
michael@0 347 }
michael@0 348
michael@0 349 SECStatus
michael@0 350 JPAKE_Round2(PLArenaPool * arena,
michael@0 351 const SECItem * p, const SECItem *q, const SECItem * gx1,
michael@0 352 const SECItem * gx3, const SECItem * gx4, SECItem * base,
michael@0 353 const SECItem * x2, const SECItem * s, SECItem * x2s)
michael@0 354 {
michael@0 355 mp_err err;
michael@0 356 mp_int P;
michael@0 357 mp_int Q;
michael@0 358 mp_int X2;
michael@0 359 mp_int S;
michael@0 360 mp_int result;
michael@0 361
michael@0 362 if (!arena ||
michael@0 363 !p || !p->data || p->len == 0 ||
michael@0 364 !q || !q->data || q->len == 0 ||
michael@0 365 !gx1 || !gx1->data || gx1->len == 0 ||
michael@0 366 !gx3 || !gx3->data || gx3->len == 0 ||
michael@0 367 !gx4 || !gx4->data || gx4->len == 0 ||
michael@0 368 !base || base->data != NULL ||
michael@0 369 (x2s != NULL && (x2s->data != NULL ||
michael@0 370 !x2 || !x2->data || x2->len == 0 ||
michael@0 371 !s || !s->data || s->len == 0))) {
michael@0 372 PORT_SetError(SEC_ERROR_INVALID_ARGS);
michael@0 373 return SECFailure;
michael@0 374 }
michael@0 375
michael@0 376 MP_DIGITS(&P) = 0;
michael@0 377 MP_DIGITS(&Q) = 0;
michael@0 378 MP_DIGITS(&X2) = 0;
michael@0 379 MP_DIGITS(&S) = 0;
michael@0 380 MP_DIGITS(&result) = 0;
michael@0 381
michael@0 382 CHECK_MPI_OK( mp_init(&P) );
michael@0 383 CHECK_MPI_OK( mp_init(&Q) );
michael@0 384 CHECK_MPI_OK( mp_init(&result) );
michael@0 385
michael@0 386 if (x2s != NULL) {
michael@0 387 CHECK_MPI_OK( mp_init(&X2) );
michael@0 388 CHECK_MPI_OK( mp_init(&S) );
michael@0 389
michael@0 390 SECITEM_TO_MPINT(*q, &Q);
michael@0 391 SECITEM_TO_MPINT(*x2, &X2);
michael@0 392
michael@0 393 SECITEM_TO_MPINT(*s, &S);
michael@0 394 /* S must be in [1, Q-1] */
michael@0 395 if (mp_cmp_z(&S) <= 0 || mp_cmp(&S, &Q) >= 0) {
michael@0 396 err = MP_BADARG;
michael@0 397 goto cleanup;
michael@0 398 }
michael@0 399
michael@0 400 CHECK_MPI_OK( mp_mulmod(&X2, &S, &Q, &result) );
michael@0 401 MPINT_TO_SECITEM(&result, x2s, arena);
michael@0 402 }
michael@0 403
michael@0 404 SECITEM_TO_MPINT(*p, &P);
michael@0 405 CHECK_MPI_OK( jpake_Round2Base(gx1, gx3, gx4, &P, &result) );
michael@0 406 MPINT_TO_SECITEM(&result, base, arena);
michael@0 407
michael@0 408 cleanup:
michael@0 409 mp_clear(&P);
michael@0 410 mp_clear(&Q);
michael@0 411 mp_clear(&X2);
michael@0 412 mp_clear(&S);
michael@0 413 mp_clear(&result);
michael@0 414
michael@0 415 if (err != MP_OKAY) {
michael@0 416 MP_TO_SEC_ERROR(err);
michael@0 417 return SECFailure;
michael@0 418 }
michael@0 419 return SECSuccess;
michael@0 420 }
michael@0 421
michael@0 422 SECStatus
michael@0 423 JPAKE_Final(PLArenaPool * arena, const SECItem * p, const SECItem * q,
michael@0 424 const SECItem * x2, const SECItem * gx4, const SECItem * x2s,
michael@0 425 const SECItem * B, SECItem * K)
michael@0 426 {
michael@0 427 mp_err err;
michael@0 428 mp_int P;
michael@0 429 mp_int Q;
michael@0 430 mp_int tmp;
michael@0 431 mp_int exponent;
michael@0 432 mp_int divisor;
michael@0 433 mp_int base;
michael@0 434
michael@0 435 if (!arena ||
michael@0 436 !p || !p->data || p->len == 0 ||
michael@0 437 !q || !q->data || q->len == 0 ||
michael@0 438 !x2 || !x2->data || x2->len == 0 ||
michael@0 439 !gx4 || !gx4->data || gx4->len == 0 ||
michael@0 440 !x2s || !x2s->data || x2s->len == 0 ||
michael@0 441 !B || !B->data || B->len == 0 ||
michael@0 442 !K || K->data != NULL) {
michael@0 443 PORT_SetError(SEC_ERROR_INVALID_ARGS);
michael@0 444 return SECFailure;
michael@0 445 }
michael@0 446
michael@0 447 MP_DIGITS(&P) = 0;
michael@0 448 MP_DIGITS(&Q) = 0;
michael@0 449 MP_DIGITS(&tmp) = 0;
michael@0 450 MP_DIGITS(&exponent) = 0;
michael@0 451 MP_DIGITS(&divisor) = 0;
michael@0 452 MP_DIGITS(&base) = 0;
michael@0 453
michael@0 454 CHECK_MPI_OK( mp_init(&P) );
michael@0 455 CHECK_MPI_OK( mp_init(&Q) );
michael@0 456 CHECK_MPI_OK( mp_init(&tmp) );
michael@0 457 CHECK_MPI_OK( mp_init(&exponent) );
michael@0 458 CHECK_MPI_OK( mp_init(&divisor) );
michael@0 459 CHECK_MPI_OK( mp_init(&base) );
michael@0 460
michael@0 461 /* exponent = -x2s (mod q) */
michael@0 462 SECITEM_TO_MPINT(*q, &Q);
michael@0 463 SECITEM_TO_MPINT(*x2s, &tmp);
michael@0 464 /* q == 0 (mod q), so q - x2s == -x2s (mod q) */
michael@0 465 CHECK_MPI_OK( mp_sub(&Q, &tmp, &exponent) );
michael@0 466
michael@0 467 /* divisor = gx4^-x2s = 1/(gx4^x2s) (mod p) */
michael@0 468 SECITEM_TO_MPINT(*p, &P);
michael@0 469 SECITEM_TO_MPINT(*gx4, &tmp);
michael@0 470 CHECK_MPI_OK( mp_exptmod(&tmp, &exponent, &P, &divisor) );
michael@0 471
michael@0 472 /* base = B*divisor = B/(gx4^x2s) (mod p) */
michael@0 473 SECITEM_TO_MPINT(*B, &tmp);
michael@0 474 CHECK_MPI_OK( mp_mulmod(&divisor, &tmp, &P, &base) );
michael@0 475
michael@0 476 /* tmp = base^x2 (mod p) */
michael@0 477 SECITEM_TO_MPINT(*x2, &exponent);
michael@0 478 CHECK_MPI_OK( mp_exptmod(&base, &exponent, &P, &tmp) );
michael@0 479
michael@0 480 MPINT_TO_SECITEM(&tmp, K, arena);
michael@0 481
michael@0 482 cleanup:
michael@0 483 mp_clear(&P);
michael@0 484 mp_clear(&Q);
michael@0 485 mp_clear(&tmp);
michael@0 486 mp_clear(&exponent);
michael@0 487 mp_clear(&divisor);
michael@0 488 mp_clear(&base);
michael@0 489
michael@0 490 if (err != MP_OKAY) {
michael@0 491 MP_TO_SEC_ERROR(err);
michael@0 492 return SECFailure;
michael@0 493 }
michael@0 494 return SECSuccess;
michael@0 495 }

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