.\"	$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>.
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.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 .