BN_generate_prime
Section: OpenSSL (3)
Updated: 20170525
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NAME
BN_generate_prime_ex, BN_is_prime_ex, BN_is_prime_fasttest_ex, BN_GENCB_call,
BN_GENCB_set_old, BN_GENCB_set, BN_generate_prime, BN_is_prime,
BN_is_prime_fasttest  generate primes and test for primality
SYNOPSIS
#include <openssl/bn.h>
int BN_generate_prime_ex(BIGNUM *ret,int bits,int safe, const BIGNUM *add,
const BIGNUM *rem, BN_GENCB *cb);
int BN_is_prime_ex(const BIGNUM *p,int nchecks, BN_CTX *ctx, BN_GENCB *cb);
int BN_is_prime_fasttest_ex(const BIGNUM *p,int nchecks, BN_CTX *ctx,
int do_trial_division, BN_GENCB *cb);
int BN_GENCB_call(BN_GENCB *cb, int a, int b);
#define BN_GENCB_set_old(gencb, callback, cb_arg) ...
#define BN_GENCB_set(gencb, callback, cb_arg) ...
Deprecated:
BIGNUM *BN_generate_prime(BIGNUM *ret, int num, int safe, BIGNUM *add,
BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);
int BN_is_prime(const BIGNUM *a, int checks, void (*callback)(int, int,
void *), BN_CTX *ctx, void *cb_arg);
int BN_is_prime_fasttest(const BIGNUM *a, int checks,
void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg,
int do_trial_division);
DESCRIPTION
BN_generate_prime_ex() generates a pseudorandom prime number of
bit length
bits.
If
ret is not
NULL, it will be used to store the number.
If cb is not NULL, it is used as follows:
 *

BN_GENCB_call(cb, 0, i) is called after generating the ith
potential prime number.
 *

While the number is being tested for primality,
BN_GENCB_call(cb, 1, j) is called as described below.
 *

When a prime has been found, BN_GENCB_call(cb, 2, i) is called.
The prime may have to fulfill additional requirements for use in
DiffieHellman key exchange:
If add is not NULL, the prime will fulfill the condition p % add
== rem (p % add == 1 if rem == NULL) in order to suit a given
generator.
If safe is true, it will be a safe prime (i.e. a prime p so
that (p1)/2 is also prime).
The PRNG must be seeded prior to calling BN_generate_prime_ex().
The prime number generation has a negligible error probability.
BN_is_prime_ex() and BN_is_prime_fasttest_ex() test if the number p is
prime. The following tests are performed until one of them shows that
p is composite; if p passes all these tests, it is considered
prime.
BN_is_prime_fasttest_ex(), when called with do_trial_division == 1,
first attempts trial division by a number of small primes;
if no divisors are found by this test and cb is not NULL,
BN_GENCB_call(cb, 1, 1) is called.
If do_trial_division == 0, this test is skipped.
Both BN_is_prime_ex() and BN_is_prime_fasttest_ex() perform a MillerRabin
probabilistic primality test with nchecks iterations. If
nchecks == BN_prime_checks, a number of iterations is used that
yields a false positive rate of at most 2^80 for random input.
If cb is not NULL, BN_GENCB_call(cb, 1, j) is called
after the jth iteration (j = 0, 1, ...). ctx is a
preallocated BN_CTX (to save the overhead of allocating and
freeing the structure in a loop), or NULL.
BN_GENCB_call calls the callback function held in the BN_GENCB structure
and passes the ints a and b as arguments. There are two types of
BN_GENCB structure that are supported: ``new'' style and ``old'' style. New
programs should prefer the ``new'' style, whilst the ``old'' style is provided
for backwards compatibility purposes.
For ``new'' style callbacks a BN_GENCB structure should be initialised with a
call to BN_GENCB_set, where gencb is a BN_GENCB *, callback is of
type int (*callback)(int, int, BN_GENCB *) and cb_arg is a void *.
``Old'' style callbacks are the same except they are initialised with a call
to BN_GENCB_set_old and callback is of type
void (*callback)(int, int, void *).
A callback is invoked through a call to BN_GENCB_call. This will check
the type of the callback and will invoke callback(a, b, gencb) for new
style callbacks or callback(a, b, cb_arg) for old style.
BN_generate_prime (deprecated) works in the same way as
BN_generate_prime_ex but expects an old style callback function
directly in the callback parameter, and an argument to pass to it in
the cb_arg. Similarly BN_is_prime and BN_is_prime_fasttest are
deprecated and can be compared to BN_is_prime_ex and
BN_is_prime_fasttest_ex respectively.
RETURN VALUES
BN_generate_prime_ex() return 1 on success or 0 on error.
BN_is_prime_ex(), BN_is_prime_fasttest_ex(), BN_is_prime() and
BN_is_prime_fasttest() return 0 if the number is composite, 1 if it is
prime with an error probability of less than 0.25^nchecks, and
1 on error.
BN_generate_prime() returns the prime number on success, NULL otherwise.
Callback functions should return 1 on success or 0 on error.
The error codes can be obtained by ERR_get_error(3).
SEE ALSO
bn(3),
ERR_get_error(3),
rand(3)
HISTORY
The
cb_arg arguments to
BN_generate_prime() and to
BN_is_prime()
were added in SSLeay 0.9.0. The
ret argument to
BN_generate_prime()
was added in SSLeay 0.9.1.
BN_is_prime_fasttest() was added in OpenSSL 0.9.5.
Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUES

 SEE ALSO

 HISTORY
