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Ensure that x**0 mod 1 = 0.

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This commit is contained in:
Adam Langley 2013-04-23 12:13:51 -04:00 committed by Ben Laurie
parent 7753a3a684
commit 2b0180c37f
2 changed files with 52 additions and 2 deletions
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7
crypto/bn/bn_exp.c
View File

@ -980,6 +980,13 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
bits = BN_num_bits(p); bits = BN_num_bits(p);
if (bits == 0) if (bits == 0)
{ {
/* x**0 mod 1 is still zero. */
if (BN_is_one(m))
{
ret = 1;
BN_zero(rr);
}
else
ret = BN_one(rr); ret = BN_one(rr);
return ret; return ret;
} }

43
crypto/bn/exptest.c
View File

@ -71,6 +71,43 @@
static const char rnd_seed[] = "string to make the random number generator think it has entropy"; static const char rnd_seed[] = "string to make the random number generator think it has entropy";
/* test_exp_mod_zero tests that x**0 mod 1 == 0. It returns zero on success. */
static int test_exp_mod_zero() {
BIGNUM a, p, m;
BIGNUM r;
BN_CTX *ctx = BN_CTX_new();
int ret = 1;
BN_init(&m);
BN_one(&m);
BN_init(&a);
BN_one(&a);
BN_init(&p);
BN_zero(&p);
BN_init(&r);
BN_mod_exp(&r, &a, &p, &m, ctx);
BN_CTX_free(ctx);
if (BN_is_zero(&r))
ret = 0;
else
{
printf("1**0 mod 1 = ");
BN_print_fp(stdout, &r);
printf(", should be 0\n");
}
BN_free(&r);
BN_free(&a);
BN_free(&p);
BN_free(&m);
return ret;
}
int main(int argc, char *argv[]) int main(int argc, char *argv[])
{ {
BN_CTX *ctx; BN_CTX *ctx;
@ -190,7 +227,13 @@ int main(int argc, char *argv[])
ERR_remove_thread_state(NULL); ERR_remove_thread_state(NULL);
CRYPTO_mem_leaks(out); CRYPTO_mem_leaks(out);
BIO_free(out); BIO_free(out);
printf("\n");
if (test_exp_mod_zero() != 0)
goto err;
printf("done\n"); printf("done\n");
EXIT(0); EXIT(0);
err: err:
ERR_load_crypto_strings(); ERR_load_crypto_strings();