- /* Copyright (c) 2017, Google Inc.
- *
- * Permission to use, copy, modify, and/or distribute this software for any
- * purpose with or without fee is hereby granted, provided that the above
- * copyright notice and this permission notice appear in all copies.
- *
- * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
- * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
- * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
- * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
- * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
- * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
- * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
-
- #include <openssl/bn.h>
- #include <openssl/bytestring.h>
- #include <openssl/mem.h>
-
- #define CHECK(expr) \
- do { \
- if (!(expr)) { \
- printf("%s failed\n", #expr); \
- abort(); \
- } \
- } while (false)
-
- // Basic implementation of mod_exp using square and multiple method.
- int mod_exp(BIGNUM *r, const BIGNUM *a, const BIGNUM *p, const BIGNUM *m,
- BN_CTX *ctx) {
- if (BN_is_one(m)) {
- BN_zero(r);
- return 1;
- }
-
- bssl::UniquePtr<BIGNUM> exp(BN_dup(p));
- bssl::UniquePtr<BIGNUM> base(BN_new());
- if (!exp || !base) {
- return 0;
- }
- if (!BN_one(r) || !BN_nnmod(base.get(), a, m, ctx)) {
- return 0;
- }
-
- while (!BN_is_zero(exp.get())) {
- if (BN_is_odd(exp.get())) {
- if (!BN_mul(r, r, base.get(), ctx) || !BN_nnmod(r, r, m, ctx)) {
- return 0;
- }
- }
- if (!BN_rshift1(exp.get(), exp.get()) ||
- !BN_mul(base.get(), base.get(), base.get(), ctx) ||
- !BN_nnmod(base.get(), base.get(), m, ctx)) {
- return 0;
- }
- }
-
- return 1;
- }
-
- extern "C" int LLVMFuzzerTestOneInput(const uint8_t *buf, size_t len) {
- CBS cbs, child0, child1, child2;
- uint8_t sign;
- CBS_init(&cbs, buf, len);
- if (!CBS_get_u16_length_prefixed(&cbs, &child0) ||
- !CBS_get_u8(&child0, &sign) ||
- CBS_len(&child0) == 0 ||
- !CBS_get_u16_length_prefixed(&cbs, &child1) ||
- CBS_len(&child1) == 0 ||
- !CBS_get_u16_length_prefixed(&cbs, &child2) ||
- CBS_len(&child2) == 0) {
- return 0;
- }
-
- // Don't fuzz inputs larger than 512 bytes (4096 bits). This isn't ideal, but
- // the naive |mod_exp| above is somewhat slow, so this otherwise causes the
- // fuzzers to spend a lot of time exploring timeouts.
- if (CBS_len(&child0) > 512 ||
- CBS_len(&child1) > 512 ||
- CBS_len(&child2) > 512) {
- return 0;
- }
-
- bssl::UniquePtr<BIGNUM> base(
- BN_bin2bn(CBS_data(&child0), CBS_len(&child0), nullptr));
- BN_set_negative(base.get(), sign % 2);
- bssl::UniquePtr<BIGNUM> power(
- BN_bin2bn(CBS_data(&child1), CBS_len(&child1), nullptr));
- bssl::UniquePtr<BIGNUM> modulus(
- BN_bin2bn(CBS_data(&child2), CBS_len(&child2), nullptr));
-
- if (BN_is_zero(modulus.get())) {
- return 0;
- }
-
- bssl::UniquePtr<BN_CTX> ctx(BN_CTX_new());
- bssl::UniquePtr<BN_MONT_CTX> mont(BN_MONT_CTX_new());
- bssl::UniquePtr<BIGNUM> result(BN_new());
- bssl::UniquePtr<BIGNUM> expected(BN_new());
- CHECK(ctx);
- CHECK(mont);
- CHECK(result);
- CHECK(expected);
-
- CHECK(mod_exp(expected.get(), base.get(), power.get(), modulus.get(),
- ctx.get()));
- CHECK(BN_mod_exp(result.get(), base.get(), power.get(), modulus.get(),
- ctx.get()));
- CHECK(BN_cmp(result.get(), expected.get()) == 0);
-
- if (BN_is_odd(modulus.get())) {
- CHECK(BN_MONT_CTX_set(mont.get(), modulus.get(), ctx.get()));
- CHECK(BN_mod_exp_mont(result.get(), base.get(), power.get(), modulus.get(),
- ctx.get(), mont.get()));
- CHECK(BN_cmp(result.get(), expected.get()) == 0);
- CHECK(BN_mod_exp_mont_consttime(result.get(), base.get(), power.get(),
- modulus.get(), ctx.get(), mont.get()));
- CHECK(BN_cmp(result.get(), expected.get()) == 0);
- }
-
- uint8_t *data = (uint8_t *)OPENSSL_malloc(BN_num_bytes(result.get()));
- BN_bn2bin(result.get(), data);
- OPENSSL_free(data);
-
- return 0;
- }
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