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Ensure that x**0 mod 1 = 0.

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This commit is contained in:
Adam Langley 2014-06-20 12:00:00 -07:00
parent ebebf87d6d
commit 61bb3ddfab
2 changed files with 47 additions and 2 deletions
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41
crypto/bn/bn_test.c
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@ -98,6 +98,7 @@ int test_mod_exp(BIO *bp, BN_CTX *ctx);
int test_mod_exp_mont_consttime(BIO *bp, BN_CTX *ctx);
int test_exp(BIO *bp, BN_CTX *ctx);
int test_mod_sqrt(BIO *bp, BN_CTX *ctx);
static int test_exp_mod_zero();
int test_mod_exp_mont5(BIO *bp, BN_CTX *ctx);
#if 0
int test_gf2m_add(BIO *bp);
@ -251,8 +252,10 @@ int main(int argc, char *argv[]) {
(void)BIO_flush(out);
message(out, "BN_exp");
if (!test_exp(out, ctx))
if (!test_exp(out, ctx) ||
!test_exp_mod_zero()) {
goto err;
}
(void)BIO_flush(out);
message(out, "BN_mod_sqrt");
@ -1117,6 +1120,42 @@ int test_exp(BIO *bp, BN_CTX *ctx) {
return (1);
}
/* test_exp_mod_zero tests that x**0 mod 1 == 0. */
static int test_exp_mod_zero() {
BIGNUM a, p, m;
BIGNUM r;
BN_CTX *ctx = BN_CTX_new();
int ret = 0;
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 = 1;
} 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;
}
static int genprime_cb(int p, int n, BN_GENCB *arg) {
char c = '*';

8
crypto/bn/exponentiation.c
View File

@ -1186,7 +1186,13 @@ int BN_mod_exp_mont_word(BIGNUM *rr, BN_ULONG a, const BIGNUM *p,
bits = BN_num_bits(p);
if (bits == 0) {
ret = BN_one(rr);
/* x**0 mod 1 is still zero. */
if (BN_is_one(m)) {
ret = 1;
BN_zero(rr);
} else {
ret = BN_one(rr);
}
return ret;
}
if (a == 0) {