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.\" ========================================================================
.\"
.IX Title "DSA_generate_parameters 3"
.TH DSA_generate_parameters 3 "2002-09-25" "1.1.0-dev" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
DSA_generate_parameters \- generate DSA parameters
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX 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
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIDSA_generate_parameters()\fR generates primes p and q and a generator g
for use in the \s-1DSA\s0.
.PP
\&\fBbits\fR is the length of the prime to be generated; the \s-1DSS\s0 allows a
maximum of 1024 bits.
.PP
If \fBseed\fR is \fB\s-1NULL\s0\fR or \fBseed_len\fR < 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 \fBseed\fR.
.PP
\&\fIDSA_generate_parameters()\fR places the iteration count in
*\fBcounter_ret\fR and a counter used for finding a generator in
*\fBh_ret\fR, unless these are \fB\s-1NULL\s0\fR.
.PP
A callback function may be used to provide feedback about the progress
of the key generation. If \fBcallback\fR is not \fB\s-1NULL\s0\fR, it will be
called as follows:
.IP "\(bu" 4
When a candidate for q is generated, \fBcallback(0, m++, cb_arg)\fR is called
(m is 0 for the first candidate).
.IP "\(bu" 4
When a candidate for q has passed a test by trial division,
\&\fBcallback(1, \-1, cb_arg)\fR is called.
While a candidate for q is tested by Miller-Rabin primality tests,
\&\fBcallback(1, i, cb_arg)\fR 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).
.IP "\(bu" 4
When a prime q has been found, \fBcallback(2, 0, cb_arg)\fR and
\&\fBcallback(3, 0, cb_arg)\fR are called.
.IP "\(bu" 4
Before a candidate for p (other than the first) is generated and tested,
\&\fBcallback(0, counter, cb_arg)\fR is called.
.IP "\(bu" 4
When a candidate for p has passed the test by trial division,
\&\fBcallback(1, \-1, cb_arg)\fR is called.
While it is tested by the Miller-Rabin primality test,
\&\fBcallback(1, i, cb_arg)\fR 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).
.IP "\(bu" 4
When p has been found, \fBcallback(2, 1, cb_arg)\fR is called.
.IP "\(bu" 4
When the generator has been found, \fBcallback(3, 1, cb_arg)\fR is called.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
\&\fIDSA_generate_parameters()\fR returns a pointer to the \s-1DSA\s0 structure, or
\&\fB\s-1NULL\s0\fR if the parameter generation fails. The error codes can be
obtained by \fIERR_get_error\fR\|(3).
.SH "BUGS"
.IX Header "BUGS"
Seed lengths > 20 are not supported.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIopenssl_dsa\fR\|(3), \fIERR_get_error\fR\|(3), \fIopenssl_rand\fR\|(3),
\&\fIDSA_free\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIDSA_generate_parameters()\fR appeared in SSLeay 0.8. The \fBcb_arg\fR
argument was added in SSLeay 0.9.0.
In versions up to OpenSSL 0.9.4, \fBcallback(1, ...)\fR was called
in the inner loop of the Miller-Rabin test whenever it reached the
squaring step (the parameters to \fBcallback\fR did not reveal how many
witnesses had been tested); since OpenSSL 0.9.5, \fBcallback(1, ...)\fR
is called as in \fIBN_is_prime\fR\|(3), i.e. once for each witness.