BN_GENERATE_PRIME(3) | OpenSSL | BN_GENERATE_PRIME(3) |

# NAME

BN_generate_prime_ex, BN_is_prime_ex, BN_is_prime_fasttest_ex, BN_GENCB_call, BN_GENCB_new, BN_GENCB_free, BN_GENCB_set_old, BN_GENCB_set, BN_GENCB_get_arg, 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); BN_GENCB *BN_GENCB_new(void); void BN_GENCB_free(BN_GENCB *cb); void BN_GENCB_set_old(BN_GENCB *gencb, void (*callback)(int, int, void *), void *cb_arg); void BN_GENCB_set(BN_GENCB *gencb, int (*callback)(int, int, BN_GENCB *), void *cb_arg); void *BN_GENCB_get_arg(BN_GENCB *cb);Deprecated:

#if OPENSSL_API_COMPAT < 0x00908000L 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); #endif

# DESCRIPTION

*BN_generate_prime_ex()*generates a pseudo-random prime number of at least 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 i-th 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.

**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_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 Miller-Rabin 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 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**. 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. A BN_GENCB structure should be created through a call to

*BN_GENCB_new()*, and freed through a call to

*BN_GENCB_free()*. 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. It is possible to obtained the argument associated with a BN_GENCB structure (set via a call to BN_GENCB_set or BN_GENCB_set_old) using BN_GENCB_get_arg. 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. BN_GENCB_new returns a pointer to a BN_GENCB structure on success, or

**NULL**otherwise. BN_GENCB_get_arg returns the argument previously associated with a BN_GENCB structure. Callback functions should return 1 on success or 0 on error. The error codes can be obtained by ERR_get_error(3).

# REMOVED FUNCTIONALITY

As of OpenSSL 1.1.0 it is no longer possible to create a BN_GENCB structure directly, as in:BN_GENCB callback;Instead applications should create a BN_GENCB structure using BN_GENCB_new:

BN_GENCB *callback; callback = BN_GENCB_new(); if(!callback) /* handle error */ ... BN_GENCB_free(callback);

# SEE ALSO

ERR_get_error(3), RAND_bytes(3)# HISTORY

*BN_GENCB_new()*,

*BN_GENCB_free()*, and

*BN_GENCB_get_arg()*were added in OpenSSL 1.1.0

# COPYRIGHT

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.2017-05-25 | 1.1.0f |