# DSA_generate_parameters.3ssl man page

DSA_generate_parameters_ex, DSA_generate_parameters — generate DSA parameters

## Synopsis

```
#include <openssl/dsa.h>
int DSA_generate_parameters_ex(DSA *dsa, int bits,
const unsigned char *seed, int seed_len,
int *counter_ret, unsigned long *h_ret,
BN_GENCB *cb);
```

Deprecated:

```
#if OPENSSL_API_COMPAT < 0x00908000L
DSA *DSA_generate_parameters(int bits, unsigned char *seed, int seed_len,
int *counter_ret, unsigned long *h_ret,
void (*callback)(int, int, void *), void *cb_arg);
#endif
```

## Description

**DSA_generate_parameters_ex()** generates primes p and q and a generator g for use in the DSA and stores the result in **dsa**.

**bits** is the length of the prime p to be generated. For lengths under 2048 bits, the length of q is 160 bits; for lengths greater than or equal to 2048 bits, the length of q is set to 256 bits.

If **seed** is NULL, or it does not generate primes, the primes will be generated at random. If **seed_len** is less than the length of q, an error is returned if old DSA parameter generation method is used as a backend.

**DSA_generate_parameters_ex()** places the iteration count in ***counter_ret** and a counter used for finding a generator in ***h_ret**, unless these are **NULL**.

A callback function may be used to provide feedback about the progress of the key generation. If **cb** is not **NULL**, it will be called as shown below. For information on the BN_GENCB structure and the BN_GENCB_call function discussed below, refer to BN_generate_prime(3).

**DSA_generate_prime()** is similar to **DSA_generate_prime_ex()** but expects an old-style callback function; see BN_generate_prime(3) for information on the old-style callback.

- When a candidate for q is generated,
**BN_GENCB_call(cb, 0, m++)**is called (m is 0 for the first candidate). - When a candidate for q has passed a test by trial division,
**BN_GENCB_call(cb, 1, -1)**is called. While a candidate for q is tested by Miller-Rabin primality tests,**BN_GENCB_call(cb, 1, i)**is called in the outer loop (once for each witness that confirms that the candidate may be prime); i is the loop counter (starting at 0). - When a prime q has been found,
**BN_GENCB_call(cb, 2, 0)**and**BN_GENCB_call(cb, 3, 0)**are called. - Before a candidate for p (other than the first) is generated and tested,
**BN_GENCB_call(cb, 0, counter)**is called. - When a candidate for p has passed the test by trial division,
**BN_GENCB_call(cb, 1, -1)**is called. While it is tested by the Miller-Rabin primality test,**BN_GENCB_call(cb, 1, i)**is called in the outer loop (once for each witness that confirms that the candidate may be prime). i is the loop counter (starting at 0). - When p has been found,
**BN_GENCB_call(cb, 2, 1)**is called. - When the generator has been found,
**BN_GENCB_call(cb, 3, 1)**is called.

## Return Values

**DSA_generate_parameters_ex()** returns a 1 on success, or 0 otherwise. The error codes can be obtained by ERR_get_error(3).

**DSA_generate_parameters()** returns a pointer to the DSA structure or **NULL** if the parameter generation fails.

## Bugs

Seed lengths greater than 20 are not supported.

## See Also

DSA_new(3), ERR_get_error(3), RAND_bytes(3), **DSA_free**(3), BN_generate_prime(3)

## History

**DSA_generate_parameters()** was deprecated in OpenSSL 0.9.8; use **DSA_generate_parameters_ex()** instead.

## Copyright

Copyright 2000-2018 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>.

## Referenced By

BN_generate_prime.3ssl(3), dsa.3ssl(3), DSA_get0_pqg.3ssl(3), DSA_meth_new.3ssl(3), DSA_new.3ssl(3).