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Numbers greater than 1 are usually non-negative.

Browse source 
BN_is_prime_fasttest_ex begins by rejecting if a <= 1. Then it goes to
set A := abs(a), but a cannot be negative at this point.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3275)
This commit is contained in:
David Benjamin 2017-04-21 12:07:03 -04:00
parent dc99b885de
commit 8b24f94209
1 changed files with 6 additions and 18 deletions
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24
crypto/bn/bn_prime.c
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@ -158,7 +158,6 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
BN_CTX *ctx = NULL;
BIGNUM *A1, *A1_odd, *check; /* taken from ctx */
BN_MONT_CTX *mont = NULL;
const BIGNUM *A = NULL;
if (BN_cmp(a, BN_value_one()) <= 0)
return 0;
@ -188,25 +187,14 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
goto err;
BN_CTX_start(ctx);
/* A := abs(a) */
if (a->neg) {
BIGNUM *t;
if ((t = BN_CTX_get(ctx)) == NULL)
goto err;
if (BN_copy(t, a) == NULL)
goto err;
t->neg = 0;
A = t;
} else
A = a;
A1 = BN_CTX_get(ctx);
A1_odd = BN_CTX_get(ctx);
check = BN_CTX_get(ctx);
if (check == NULL)
goto err;
/* compute A1 := A - 1 */
if (!BN_copy(A1, A))
/* compute A1 := a - 1 */
if (!BN_copy(A1, a))
goto err;
if (!BN_sub_word(A1, 1))
goto err;
@ -222,11 +210,11 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
if (!BN_rshift(A1_odd, A1, k))
goto err;
/* Montgomery setup for computations mod A */
/* Montgomery setup for computations mod a */
mont = BN_MONT_CTX_new();
if (mont == NULL)
goto err;
if (!BN_MONT_CTX_set(mont, A, ctx))
if (!BN_MONT_CTX_set(mont, a, ctx))
goto err;
for (i = 0; i < checks; i++) {
@ -234,9 +222,9 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
goto err;
if (!BN_add_word(check, 1))
goto err;
/* now 1 <= check < A */
/* now 1 <= check < a */
j = witness(check, A, A1, A1_odd, k, ctx, mont);
j = witness(check, a, A1, A1_odd, k, ctx, mont);
if (j == -1)
goto err;
if (j) {