=pod

=head1 NAME

DSA_sign, DSA_sign_setup, DSA_verify - DSA signatures

=head1 SYNOPSIS

 #include <openssl/dsa.h>

 int DSA_sign(int type, const unsigned char *dgst, int len,
              unsigned char *sigret, unsigned int *siglen, DSA *dsa);

 int DSA_sign_setup(DSA *dsa, BN_CTX *ctx, BIGNUM **kinvp, BIGNUM **rp);

 int DSA_verify(int type, const unsigned char *dgst, int len,
                unsigned char *sigbuf, int siglen, DSA *dsa);

=head1 DESCRIPTION

DSA_sign() computes a digital signature on the B<len> byte message
digest B<dgst> using the private key B<dsa> and places its ASN.1 DER
encoding at B<sigret>. The length of the signature is places in
*B<siglen>. B<sigret> must point to DSA_size(B<dsa>) bytes of memory.

DSA_sign_setup() is defined only for backward binary compatibility and
should not be used.
Since OpenSSL 1.1.0 the DSA type is opaque and the output of
DSA_sign_setup() cannot be used anyway: calling this function will only
cause overhead, and does not affect the actual signature
(pre-)computation.

DSA_verify() verifies that the signature B<sigbuf> of size B<siglen>
matches a given message digest B<dgst> of size B<len>.
B<dsa> is the signer's public key.

The B<type> parameter is ignored.

The random generator must be seeded when DSA_sign() (or DSA_sign_setup())
is called.
If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
external circumstances (see L<RAND(7)>), the operation will fail.

=head1 RETURN VALUES

DSA_sign() and DSA_sign_setup() return 1 on success, 0 on error.
DSA_verify() returns 1 for a valid signature, 0 for an incorrect
signature and -1 on error. The error codes can be obtained by
L<ERR_get_error(3)>.

=head1 CONFORMING TO

US Federal Information Processing Standard FIPS 186 (Digital Signature
Standard, DSS), ANSI X9.30

=head1 SEE ALSO

L<DSA_new(3)>, L<ERR_get_error(3)>, L<RAND_bytes(3)>,
L<DSA_do_sign(3)>,
L<RAND(7)>

=head1 COPYRIGHT

Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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