NAME

DSA_generate_parameters − Generate DSA parameters

SYNOPSIS

#include <openssl/dsa.h>
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 );

DESCRIPTION

The DSA_generate_parameters() function generates primes p and q and a generator g for use in the DSA. 

The value of 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. 

The DSA_generate_parameters() function 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 callback is not NULL, it will be called as follows:

       •When a candidate for q is generated, callback(0, m++, cb_arg) is called (m is 0 for the first candidate). 

       •When a candidate for q has passed a test by trial division, callback(1, -1, cb_arg) is called. While a candidate for q is tested by Miller-Rabin primality tests, callback(1, i, cb_arg) 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, callback(2, 0, cb_arg) and callback(3, 0, cb_arg) are called. 

       •Before a candidate for p (other than the first) is generated and tested, callback(0, counter, cb_arg) is called. 

       •When a candidate for p has passed the test by trial division, callback(1, -1, cb_arg) is called. While it is tested by the Miller-Rabin primality test, callback(1, i, cb_arg) 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, callback(2, 1, cb_arg) is called. 

       •When the generator has been found, callback(3, 1, cb_arg) is called. 

RESTRICTIONS

Seed lengths > 20 are not supported. 

RETURN VALUE

The DSA_generate_parameters() function returns a pointer to the DSA structure, or NULL if the parameter generation fails. The error codes can be obtained from ERR_get_error(). 

HISTORY

The DSA_generate_parameters() function appeared in SSLeay 0.8. The cb_arg argument was added in SSLeay 0.9.0.  In versions up to OpenSSL 0.9.4, callback(1, ...) was called in the inner loop of the Miller-Rabin test whenever it reached the squaring step (the parameters to callback did not reveal how many witnesses had been tested); since OpenSSL 0.9.5, callback(1, ...) is called as in BN_is_prime(3), meaning once for each witness. 

SEE ALSO

Functions: dsa(3), err(3), rand(3), DSA_free(3)