DSA_generate_parameters.3 revision 279265
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Title "DSA_generate_parameters 3"
DSA_generate_parameters 3 "2015-01-08" "0.9.8zd" "OpenSSL"
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"NAME"
DSA_generate_parameters - generate DSA parameters
"SYNOPSIS"
Header "SYNOPSIS" .Vb 1 #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); .Ve
"DESCRIPTION"
Header "DESCRIPTION" \fIDSA_generate_parameters() generates primes p and q and a generator g for use in the \s-1DSA.\s0

\fBbits is the length of the prime to be generated; the \s-1DSS\s0 allows a maximum of 1024 bits.

If seed is \s-1NULL\s0 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.

\fIDSA_generate_parameters() places the iteration count in *counter_ret and a counter used for finding a generator in *h_ret, unless these are \s-1NULL\s0.

A callback function may be used to provide feedback about the progress of the key generation. If callback is not \s-1NULL\s0, it will be called as follows:

"\(bu" 4
When a candidate for q is generated, callback(0, m++, cb_arg) is called (m is 0 for the first candidate).
"\(bu" 4
When a candidate for q has passed a test by trial division, \fBcallback(1, -1, cb_arg) is called. While a candidate for q is tested by Miller-Rabin primality tests, \fBcallback(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).
"\(bu" 4
When a prime q has been found, callback(2, 0, cb_arg) and \fBcallback(3, 0, cb_arg) are called.
"\(bu" 4
Before a candidate for p (other than the first) is generated and tested, \fBcallback(0, counter, cb_arg) is called.
"\(bu" 4
When a candidate for p has passed the test by trial division, \fBcallback(1, -1, cb_arg) is called. While it is tested by the Miller-Rabin primality test, \fBcallback(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).
"\(bu" 4
When p has been found, callback(2, 1, cb_arg) is called.
"\(bu" 4
When the generator has been found, callback(3, 1, cb_arg) is called.
"RETURN VALUE"
Header "RETURN VALUE" \fIDSA_generate_parameters() returns a pointer to the \s-1DSA\s0 structure, or \fB\s-1NULL\s0 if the parameter generation fails. The error codes can be obtained by ERR_get_error\|(3).
"BUGS"
Header "BUGS" Seed lengths > 20 are not supported.
"SEE ALSO"
Header "SEE ALSO" \fIdsa\|(3), ERR_get_error\|(3), rand\|(3), \fIDSA_free\|(3)
"HISTORY"
Header "HISTORY" \fIDSA_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.