# dsa_generate_parameters(3ssl) [debian man page]

DSA_generate_parameters(3SSL) OpenSSL DSA_generate_parameters(3SSL)NAME

DSA_generate_parameters - generate DSA parametersSYNOPSIS

#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

DSA_generate_parameters() generates primes p and q and a generator g for use in the 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() 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: o When a candidate for q is generated, callback(0, m++, cb_arg) is called (m is 0 for the first candidate). o When a candidate for q has passed a test by trial division, callback(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). o When a prime q has been found, callback(2, 0, cb_arg) and callback(3, 0, cb_arg) are called. o Before a candidate for p (other than the first) is generated and tested, callback(0, counter, cb_arg) is called. o 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). o When p has been found, callback(2, 1, cb_arg) is called. o When the generator has been found, callback(3, 1, cb_arg) is called.-1RETURN VALUE

DSA_generate_parameters() returns a pointer to the DSA structure, or NULL if the parameter generation fails. The error codes can be obtained by ERR_get_error(3).BUGS

Seed lengths > 20 are not supported.SEE ALSO

dsa(3), ERR_get_error(3), rand(3), DSA_free(3)HISTORY

DSA_generate_parameters() 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), i.e. once for each witness.1.0.1e2013-02-11 DSA_generate_parameters(3SSL)

## Check Out this Related Man Page

BN_generate_prime(3SSL) OpenSSL BN_generate_prime(3SSL)NAME

BN_generate_prime, BN_is_prime, BN_is_prime_fasttest - generate primes and test for primalitySYNOPSIS

#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

BN_generate_prime() 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: o callback(0, i, cb_arg) is called after generating the i-th potential prime number. o While the number is being tested for primality, callback(1, j, cb_arg) is called as described below. o 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,, 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_checks, 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.-1RETURN VALUES

BN_generate_prime() returns the prime number on success, NULL otherwise. BN_is_prime() returns 0 if the number is composite, 1 if it is prime with an error probability of less than 0.25^checks, andon error. The error codes can be obtained by ERR_get_error(3).-1SEE ALSO

bn(3), ERR_get_error(3), rand(3)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. BN_is_prime_fasttest() was added in OpenSSL 0.9.5.1.0.1e2013-02-11 BN_generate_prime(3SSL)