DSA_GENERATE_PARAMETERS_EX(3) | Library Functions Manual | DSA_GENERATE_PARAMETERS_EX(3)

# NAME

`DSA_generate_parameters_ex` — generate DSA parameters

# SYNOPSIS

library “libcrypto”
`#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);

# 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 to be generated; the DSS allows a maximum of 1024 bits.

If seed is `NULL` or seed_len < 20, the primes will be generated at random. Otherwise, the seed is used to generate them. If the given seed does not yield a prime q, a new random seed is chosen and placed at seed.

`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, refer to BN_GENCB_call(3).

- 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).

# SEE ALSO

BN_generate_prime(3), DSA_get0_pqg(3), DSA_new(3)

# HISTORY

`DSA_generate_parameters_ex`() first appeared in OpenSSL 0.9.8 and has been available since OpenBSD 4.5.

# BUGS

Seed lengths > 20 are not supported.

June 8, 2025 | Debian