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.\" $OpenBSD: DSA_do_sign.3,v 1.8 2018/03/21 17:57:48 schwarze Exp $
.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
.\"
.\" This file was written by Ulf Moeller <ulf@openssl.org>.
.\" Copyright (c) 2000 The OpenSSL Project. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in
.\" the documentation and/or other materials provided with the
.\" distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\" software must display the following acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\" endorse or promote products derived from this software without
.\" prior written permission. For written permission, please contact
.\" openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\" nor may "OpenSSL" appear in their names without prior written
.\" permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\" acknowledgment:
.\" "This product includes software developed by the OpenSSL Project
.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: March 21 2018 $
.Dt DSA_DO_SIGN 3
.Os
.Sh NAME
.Nm DSA_do_sign ,
.Nm DSA_do_verify
.Nd raw DSA signature operations
.Sh SYNOPSIS
.In openssl/dsa.h
.Ft DSA_SIG *
.Fo DSA_do_sign
.Fa "const unsigned char *dgst"
.Fa "int dlen"
.Fa "DSA *dsa"
.Fc
.Ft int
.Fo DSA_do_verify
.Fa "const unsigned char *dgst"
.Fa "int dgst_len"
.Fa "DSA_SIG *sig"
.Fa "DSA *dsa"
.Fc
.Sh DESCRIPTION
.Fn DSA_do_sign
computes a digital signature on the
.Fa dlen
byte message digest
.Fa dgst
using the private key
.Fa dsa
and returns it in a newly allocated
.Vt DSA_SIG
structure.
.Pp
.Xr DSA_sign_setup 3
may be used to precompute part of the signing operation in case
signature generation is time-critical.
.Pp
.Fn DSA_do_verify
verifies that the signature
.Fa sig
matches a given message digest
.Fa dgst
of size
.Fa dgst_len .
.Fa dsa
is the signer's public key.
.Sh RETURN VALUES
.Fn DSA_do_sign
returns the signature or
.Dv NULL
on error.
.Fn DSA_do_verify
returns 1 for a valid signature, 0 for an incorrect signature,
and -1 on error.
The error codes can be obtained by
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr DSA_get0_key 3 ,
.Xr DSA_meth_set_sign 3 ,
.Xr DSA_new 3 ,
.Xr DSA_SIG_new 3 ,
.Xr DSA_sign 3 ,
.Xr ERR_get_error 3 ,
.Xr RAND_bytes 3
.Sh HISTORY
.Fn DSA_do_sign
and
.Fn DSA_do_verify
first appeared in OpenSSL 0.9.3 and have been available since
.Ox 2.6 .
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