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.\" $OpenBSD: EVP_DigestVerifyInit.3,v 1.8 2019/06/10 14:58:48 schwarze Exp $
.\" OpenSSL fb552ac6 Sep 30 23:43:01 2009 +0000
.\"
.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
.\" Copyright (c) 2006, 2009, 2014, 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: June 10 2019 $
.Dt EVP_DIGESTVERIFYINIT 3
.Os
.Sh NAME
.Nm EVP_DigestVerifyInit ,
.Nm EVP_DigestVerifyUpdate ,
.Nm EVP_DigestVerifyFinal
.Nd EVP signature verification functions
.Sh SYNOPSIS
.In openssl/evp.h
.Ft int
.Fo EVP_DigestVerifyInit
.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_DigestVerifyUpdate
.Fa "EVP_MD_CTX *ctx"
.Fa "const void *d"
.Fa "size_t cnt"
.Fc
.Ft int
.Fo EVP_DigestVerifyFinal
.Fa "EVP_MD_CTX *ctx"
.Fa "const 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_DigestVerifyInit
sets up verification context
.Fa ctx
to use digest
.Fa type
from
.Vt ENGINE
.Fa e
and public 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 verification operation will be written to
.Pf * Fa pctx :
this can be used to set alternative verification options.
.Pp
.Fn EVP_DigestVerifyUpdate
hashes
.Fa cnt
bytes of data at
.Fa d
into the verification 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_DigestVerifyFinal
verifies the data in
.Fa ctx
against the signature in
.Fa sig
of length
.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_DigestVerifyFinal
internally finalizes a copy of the digest context.
This means that
.Xr EVP_VerifyUpdate 3
and
.Xr EVP_VerifyFinal 3
can be called later to digest and verify 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_free 3
or a memory leak will occur.
.Sh RETURN VALUES
.Fn EVP_DigestVerifyInit
and
.Fn EVP_DigestVerifyUpdate
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
.Fn EVP_DigestVerifyFinal
returns 1 for success; any other value indicates failure.
A return value of 0 indicates that the signature did not verify
successfully (that is, the signature did not match the original
data or the signature had an invalid form), while other values
indicate a more serious error (and sometimes also indicate an invalid
signature form).
.Pp
The error codes can be obtained from
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr evp 3 ,
.Xr EVP_DigestInit 3 ,
.Xr EVP_DigestSignInit 3 ,
.Xr EVP_PKEY_meth_set_verifyctx 3
.Sh HISTORY
.Fn EVP_DigestVerifyInit ,
.Fn EVP_DigestVerifyUpdate ,
and
.Fn EVP_DigestVerifyFinal
first appeared in OpenSSL 1.0.0 and have been available since
.Ox 4.9 .
|
