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.\" $OpenBSD: EVP_DigestSignInit.3,v 1.3 2016/11/26 17:38:55 schwarze Exp $
.\" OpenSSL 9b86974e Aug 17 15:21:33 2015 -0400
.\"
.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
.\" Copyright (c) 2006, 2009, 2015, 2016 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: November 26 2016 $
.Dt EVP_DIGESTSIGNINIT 3
.Os
.Sh NAME
.Nm EVP_DigestSignInit ,
.Nm EVP_DigestSignUpdate ,
.Nm EVP_DigestSignFinal
.Nd EVP signing functions
.Sh SYNOPSIS
.In openssl/evp.h
.Ft int
.Fo EVP_DigestSignInit
.Fa "EVP_MD_CTX *ctx"
.Fa "EVP_PKEY_CTX **pctx"
.Fa "const EVP_MD *type"
.Fa "ENGINE *e"
.Fa "EVP_PKEY *pkey"
.Fc
.Ft int
.Fo EVP_DigestSignUpdate
.Fa "EVP_MD_CTX *ctx"
.Fa "const void *d"
.Fa "size_t cnt"
.Fc
.Ft int
.Fo EVP_DigestSignFinal
.Fa "EVP_MD_CTX *ctx"
.Fa "unsigned char *sig"
.Fa "size_t *siglen"
.Fc
.Sh DESCRIPTION
The EVP signature routines are a high level interface to digital
signatures.
.Pp
.Fn EVP_DigestSignInit
sets up the signing context
.Fa ctx
to use the digest
.Fa type
from
.Vt ENGINE
.Fa e
and private key
.Fa pkey .
.Fa ctx
must be initialized with
.Xr EVP_MD_CTX_init 3
before calling this function.
If
.Fa pctx
is not
.Dv NULL ,
the
.Vt EVP_PKEY_CTX
of the signing operation will be written to
.Pf * Fa pctx :
this can be used to set alternative signing options.
.Pp
.Fn EVP_DigestSignUpdate
hashes
.Fa cnt
bytes of data at
.Fa d
into the signature context
.Fa ctx .
This function can be called several times on the same
.Fa ctx
to include additional data.
This function is currently implemented using a macro.
.Pp
.Fn EVP_DigestSignFinal
signs the data in
.Fa ctx
and places the signature in
.Fa sig .
If
.Fa sig
is
.Dv NULL ,
then the maximum size of the output buffer is written to
.Pf * Fa siglen .
If
.Fa sig
is not
.Dv NULL ,
then before the call
.Fa siglen
should contain the length of the
.Fa sig
buffer.
If the call is successful, the signature is written to
.Fa sig
and the amount of data written to
.Fa siglen .
.Pp
The EVP interface to digital signatures should almost always be
used in preference to the low level interfaces.
This is because the code then becomes transparent to the algorithm used
and much more flexible.
.Pp
In previous versions of OpenSSL, there was a link between message digest
types and public key algorithms.
This meant that "clone" digests such as
.Xr EVP_dss1 3
needed to be used to sign using SHA1 and DSA.
This is no longer necessary and the use of clone digest is now
discouraged.
.Pp
The call to
.Fn EVP_DigestSignFinal
internally finalizes a copy of the digest context.
This means that
.Fn EVP_DigestSignUpdate
and
.Fn EVP_DigestSignFinal
can be called later to digest and sign additional data.
.Pp
Since only a copy of the digest context is ever finalized, the context
must be cleaned up after use by calling
.Xr EVP_MD_CTX_cleanup 3 ,
or a memory leak will occur.
.Pp
The use of
.Xr EVP_PKEY_size 3
with these functions is discouraged because some signature operations
may have a signature length which depends on the parameters set.
As a result,
.Xr EVP_PKEY_size 3
would have to return a value which indicates the maximum possible
signature for any set of parameters.
.Sh RETURN VALUES
.Fn EVP_DigestSignInit ,
.Fn EVP_DigestSignUpdate ,
and
.Fn EVP_DigestSignFinal
return 1 for success and 0 or a negative value for failure.
In particular, a return value of -2 indicates the operation is not
supported by the public key algorithm.
.Pp
The error codes can be obtained from
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr ERR 3 ,
.Xr evp 3 ,
.Xr EVP_DigestInit 3 ,
.Xr EVP_DigestVerifyInit 3
.Sh HISTORY
.Fn EVP_DigestSignInit ,
.Fn EVP_DigestSignUpdate ,
and
.Fn EVP_DigestSignFinal
were first added to OpenSSL 1.0.0.
|
