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DSA_generate_parameters(3)


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)

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