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@@ -154,19 +154,21 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
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int i, j, ret = -1;
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int k;
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BN_CTX *ctx = NULL;
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- BIGNUM *A1, *A1_odd, *check; /* taken from ctx */
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+ BIGNUM *A1, *A1_odd, *A3, *check; /* taken from ctx */
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BN_MONT_CTX *mont = NULL;
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- if (BN_cmp(a, BN_value_one()) <= 0)
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+ /* Take care of the really small primes 2 & 3 */
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+ if (BN_is_word(a, 2) || BN_is_word(a, 3))
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+ return 1;
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+
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+ /* Check odd and bigger than 1 */
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+ if (!BN_is_odd(a) || BN_cmp(a, BN_value_one()) <= 0)
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return 0;
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if (checks == BN_prime_checks)
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checks = BN_prime_checks_for_size(BN_num_bits(a));
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/* first look for small factors */
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- if (!BN_is_odd(a))
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- /* a is even => a is prime if and only if a == 2 */
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- return BN_is_word(a, 2);
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if (do_trial_division) {
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for (i = 1; i < NUMPRIMES; i++) {
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BN_ULONG mod = BN_mod_word(a, primes[i]);
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@@ -186,20 +188,18 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
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BN_CTX_start(ctx);
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A1 = BN_CTX_get(ctx);
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+ A3 = BN_CTX_get(ctx);
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A1_odd = BN_CTX_get(ctx);
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check = BN_CTX_get(ctx);
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if (check == NULL)
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goto err;
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/* compute A1 := a - 1 */
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- if (!BN_copy(A1, a))
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- goto err;
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- if (!BN_sub_word(A1, 1))
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+ if (!BN_copy(A1, a) || !BN_sub_word(A1, 1))
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goto err;
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- if (BN_is_zero(A1)) {
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- ret = 0;
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+ /* compute A3 := a - 3 */
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+ if (!BN_copy(A3, a) || !BN_sub_word(A3, 3))
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goto err;
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- }
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/* write A1 as A1_odd * 2^k */
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k = 1;
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@@ -216,11 +216,9 @@ int BN_is_prime_fasttest_ex(const BIGNUM *a, int checks, BN_CTX *ctx_passed,
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goto err;
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for (i = 0; i < checks; i++) {
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- if (!BN_priv_rand_range(check, A1))
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- goto err;
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- if (!BN_add_word(check, 1))
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+ /* 1 < check < a-1 */
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+ if (!BN_priv_rand_range(check, A3) || !BN_add_word(check, 2))
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goto err;
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- /* now 1 <= check < a */
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j = witness(check, a, A1, A1_odd, k, ctx, mont);
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if (j == -1)
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