NAME

       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:

        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_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.

       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).

       •   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.

       DSA_generate_parameters() (deprecated) works in much the  same  way  as  for  DSA_generate_parameters_ex,
       except  that  no  dsa  parameter  is  passed  and  instead  a  newly allocated DSA structure is returned.
       Additionally "old style" callbacks are used instead of the  newer  BN_GENCB  based  approach.   Refer  to
       BN_generate_prime(3) for further information.

RETURN VALUE

       DSA_generate_parameters_ex() returns a 1 on success, or 0 otherwise.

       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), BN_generate_prime(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.

1.0.2g                                             2016-03-01                      DSA_generate_parameters(3SSL)