NAME    [Toc]    [Back]

       DSA_generate_parameters - Generate DSA parameters

SYNOPSIS    [Toc]    [Back]

       #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    [Toc]    [Back]

       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  MillerRabin
 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    [Toc]    [Back]

       Seed lengths > 20 are not supported.

RETURN VALUE    [Toc]    [Back]

       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    [Toc]    [Back]

       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    [Toc]    [Back]

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



                                       DSA_generate_parameters(3)