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BN_generate_prime(3)
NAME
  BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - Generate primes and
  test for primality

SYNOPSIS
  #include <openssl/bn.h>

  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
  The BN_generate_prime() function generates a pseudo-random prime number of
  num bits. If ret is not NULL, it will be used to store the number.

  If callback is not NULL, it is called as follows:

    ·  callback(0, i, cb_arg) is called after generating the i-th potential
       prime number.

    ·  While the number is being tested for primality, callback(1, j, cb_arg)
       is called as described below.

    ·  When a prime has been found, callback(2, i, cb_arg) is called.

  The prime may have to fulfill additional requirements for use in Diffie-
  Hellman 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 (p-1)/2 is
  also prime).

  The PRNG must be seeded prior to calling BN_generate_prime(). The prime
  number generation has a negligible error probability.

  BN_is_prime() and BN_is_prime_fasttest() test if the number a is prime.
  The following tests are performed until one of them shows that a is
  composite; if a passes all these tests, it is considered prime.

  BN_is_prime_fasttest(), 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 callback is not NULL, callback(1, -1, cb_arg) is
  called. If do_trial_division == 0, this test is skipped.

  Both BN_is_prime() and BN_is_prime_fasttest() perform a Miller-Rabin
  probabilistic primality test with checks iterations. If checks ==
  BN_prime_check, a number of iterations is used that yields a false positive
  rate of at most 2^-80 for random input.

  If callback is not NULL, callback(1, j, cb_arg) is called after the j-th
  iteration (j = 0, 1, ...).  ctx is a pre-allocated BN_CTX (to save the
  overhead of allocating and freeing the structure in a loop), or NULL.

RETURN VALUES
  The BN_generate_prime() function returns the prime number on success, NULL
  otherwise.

  The BN_is_prime() function returns 0 if the number is composite, 1 if it is
  prime with an error probability of less than 0.25^checks, and -1 on error.

  The error codes can be obtained by using the ERR_get_error() function.

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. The BN_is_prime_fasttest() function was added in OpenSSL
  0.9.5.

SEE ALSO
  Functions: bn(3), err(3), rand(3)

Index for Section 3

Alphabetical listing for B

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