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Generate safe primes not divisible by 3, 5 or 7.

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~2% speed improvement on trial division.
This commit is contained in:
Felix Laurie von Massenbach
2014-05-27 02:12:59 +01:00
committed by Ben Laurie
parent b0513819e0
commit c09ec5d2a0
3 changed files with 21 additions and 11 deletions
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2
crypto/bn/bn_lcl.h
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@@ -536,7 +536,7 @@ BIGNUM *int_bn_mod_inverse(BIGNUM *in,
int bn_probable_prime_dh(BIGNUM *rnd, int bits,
const BIGNUM *add, const BIGNUM *rem, BN_CTX *ctx);
int bn_probable_prime_dh_coprime(BIGNUM *rnd, int bits,
int bn_probable_prime_dh_coprime_safe(BIGNUM *rnd, int bits,
const BIGNUM *add, const BIGNUM *rem, BN_CTX *ctx);
#ifdef __cplusplus

22
crypto/bn/bn_prime.c
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@@ -134,7 +134,10 @@ static int probable_prime_dh(BIGNUM *rnd, const BIGNUM *add,
static int probable_prime_dh_safe(BIGNUM *rnd, int bits,
const BIGNUM *add, const BIGNUM *rem, BN_CTX *ctx);
static int prime_offsets[8] = { 7, 11, 13, 17, 19, 23, 29, 31 };
static int prime_multiplier = 210;
static int prime_offsets[8] = { 23, 47, 59, 83, 107, 143, 167, 179 };
static int prime_offset_count = 8;
static int prime_offset_count_exponent = 3;
int BN_GENCB_call(BN_GENCB *cb, int a, int b)
{
@@ -372,20 +375,27 @@ int bn_probable_prime_dh(BIGNUM *rnd, int bits,
return(probable_prime_dh(rnd, add, rem, ctx, 1));
}
int bn_probable_prime_dh_coprime(BIGNUM *rnd, int bits,
int bn_probable_prime_dh_coprime_safe(BIGNUM *rnd, int bits,
const BIGNUM *add, const BIGNUM *rem, BN_CTX *ctx)
{
int i = prime_offset_count;
BIGNUM *offset_index = BN_new();
if (!BN_rand(rnd, bits, 0, 1)) return(0);
if (!BN_rand(offset_index, 3, -1, -1)) return(0);
while (i >= prime_offset_count)
{
if (!BN_rand(offset_index, prime_offset_count_exponent, -1, -1))
return(0);
i = BN_get_word(offset_index);
}
BN_mul_word(rnd, 30);
BN_add_word(rnd, prime_offsets[BN_get_word(offset_index)]);
BN_mul_word(rnd, prime_multiplier);
BN_add_word(rnd, prime_offsets[i]);
BN_free(offset_index);
return(probable_prime_dh(rnd, add, rem, ctx, 3));
return(probable_prime_dh(rnd, add, rem, ctx, 4));
}
static int witness(BIGNUM *w, const BIGNUM *a, const BIGNUM *a1,