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.IX Title "DSA_generate_parameters 3"
.TH DSA_generate_parameters 3 2019-12-20 1.0.2u OpenSSL
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH NAME
DSA_generate_parameters_ex, DSA_generate_parameters \- generate DSA parameters
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.PP
Deprecated:
.PP
.Vb 3
\& 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"
\&\fBDSA_generate_parameters_ex()\fR generates primes p and q and a generator g
for use in the DSA and stores the result in \fBdsa\fR.
.PP
\&\fBbits\fR is the length of the prime to be generated; the DSS allows a
maximum of 1024 bits.
.PP
If \fBseed\fR is \fBNULL\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.
.PP
\&\fBDSA_generate_parameters_ex()\fR places the iteration count in
*\fBcounter_ret\fR and a counter used for finding a generator in
*\fBh_ret\fR, unless these are \fBNULL\fR.
.PP
A callback function may be used to provide feedback about the progress
of the key generation. If \fBcb\fR is not \fBNULL\fR, it will be
called as shown below. For information on the BN_GENCB structure and the
BN_GENCB_call function discussed below, refer to
\&\fBBN_generate_prime\fR\|(3).
.IP \(bu 4
When a candidate for q is generated, \fBBN_GENCB_call(cb, 0, m++)\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,
\&\fBBN_GENCB_call(cb, 1, \-1)\fR is called.
While a candidate for q is tested by Miller-Rabin primality tests,
\&\fBBN_GENCB_call(cb, 1, i)\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, \fBBN_GENCB_call(cb, 2, 0)\fR and
\&\fBBN_GENCB_call(cb, 3, 0)\fR are called.
.IP \(bu 4
Before a candidate for p (other than the first) is generated and tested,
\&\fBBN_GENCB_call(cb, 0, counter)\fR is called.
.IP \(bu 4
When a candidate for p has passed the test by trial division,
\&\fBBN_GENCB_call(cb, 1, \-1)\fR is called.
While it is tested by the Miller-Rabin primality test,
\&\fBBN_GENCB_call(cb, 1, i)\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, \fBBN_GENCB_call(cb, 2, 1)\fR is called.
.IP \(bu 4
When the generator has been found, \fBBN_GENCB_call(cb, 3, 1)\fR is called.
.PP
\&\fBDSA_generate_parameters()\fR (deprecated) works in much the same way as for DSA_generate_parameters_ex, except that no \fBdsa\fR parameter is passed and
instead a newly allocated \fBDSA\fR structure is returned. Additionally "old
style" callbacks are used instead of the newer BN_GENCB based approach.
Refer to \fBBN_generate_prime\fR\|(3) for further information.
.SH "RETURN VALUE"
.IX Header "RETURN VALUE"
\&\fBDSA_generate_parameters_ex()\fR returns a 1 on success, or 0 otherwise.
.PP
\&\fBDSA_generate_parameters()\fR returns a pointer to the DSA structure, or
\&\fBNULL\fR if the parameter generation fails.
.PP
The error codes can be obtained by \fBERR_get_error\fR\|(3).
.SH BUGS
.IX Header "BUGS"
Seed lengths > 20 are not supported.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBdsa\fR\|(3), \fBERR_get_error\fR\|(3), \fBrand\fR\|(3),
\&\fBDSA_free\fR\|(3), \fBBN_generate_prime\fR\|(3)
.SH HISTORY
.IX Header "HISTORY"
\&\fBDSA_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 \fBBN_is_prime\fR\|(3), i.e. once for each witness.