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-rw-r--r--security/nss/fuzz/mpi_invmod_target.cc69
1 files changed, 69 insertions, 0 deletions
diff --git a/security/nss/fuzz/mpi_invmod_target.cc b/security/nss/fuzz/mpi_invmod_target.cc
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * This target fuzzes NSS mpi against openssl bignum.
+ * It therefore requires openssl to be installed.
+ */
+
+#include "mpi_helper.h"
+#include "mpprime.h"
+
+#include <algorithm>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+ // We require at least size 4 to get everything we need from data.
+ if (size < 4) {
+ return 0;
+ }
+
+ INIT_THREE_NUMBERS
+
+ // Make a prime of length size.
+ int count = 0;
+ mp_err res = MP_NO;
+ // mpp_make_prime is so slow :( use something smaller than size.
+ int primeLen = std::max(static_cast<int>(size / 4), 3);
+ uint8_t bp[primeLen];
+ memcpy(bp, data, primeLen);
+ do {
+ bp[0] |= 0x80; /* set high-order bit */
+ bp[primeLen - 1] |= 0x01; /* set low-order bit */
+ ++count;
+ assert(mp_read_unsigned_octets(&b, bp, primeLen) == MP_OKAY);
+ } while ((res = mpp_make_prime(&b, primeLen * 8, PR_FALSE)) != MP_YES &&
+ count < 10);
+ if (res != MP_YES) {
+ return 0;
+ }
+
+ // Use the same prime in OpenSSL B
+ char tmp[max_size];
+ mp_toradix(&b, tmp, 16);
+ int tmpLen;
+ assert((tmpLen = BN_hex2bn(&B, tmp)) != 0);
+
+ // Compare with OpenSSL invmod
+ res = mp_invmod(&a, &b, &c);
+ BIGNUM *X = BN_mod_inverse(C, A, B, ctx);
+ if (res != MP_OKAY) {
+ // In case we couldn't compute the inverse, OpenSSL shouldn't be able to
+ // either.
+ assert(X == nullptr);
+ } else {
+ check_equal(C, &c, max_size);
+
+ // Check a * c mod b == 1
+ assert(mp_mulmod(&a, &c, &b, &c) == MP_OKAY);
+ bool eq = mp_cmp_d(&c, 1) == 0;
+ if (!eq) {
+ char cC[max_size];
+ mp_tohex(&c, cC);
+ std::cout << "c = " << std::hex << cC << std::endl;
+ }
+ assert(eq);
+ }
+
+ CLEANUP_AND_RETURN_THREE
+}