=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 Apache License 2.0 (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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