209 lines
5.9 KiB
Groff
209 lines
5.9 KiB
Groff
.\" $OpenBSD: EVP_SignInit.3,v 1.17 2023/11/16 20:27:43 schwarze Exp $
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.\" full merge up to: OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
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.\" selective merge up to: OpenSSL 79b49fb0 Mar 20 10:03:10 2018 +1000
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.\"
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.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
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.\" Copyright (c) 2000-2002, 2005, 2006, 2014-2016 The OpenSSL Project.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\"
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" 3. All advertising materials mentioning features or use of this
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.\" software must display the following acknowledgment:
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.\" "This product includes software developed by the OpenSSL Project
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.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
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.\"
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.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
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.\" endorse or promote products derived from this software without
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.\" prior written permission. For written permission, please contact
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.\" openssl-core@openssl.org.
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.\"
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.\" 5. Products derived from this software may not be called "OpenSSL"
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.\" nor may "OpenSSL" appear in their names without prior written
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.\" permission of the OpenSSL Project.
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.\"
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.\" 6. Redistributions of any form whatsoever must retain the following
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.\" acknowledgment:
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.\" "This product includes software developed by the OpenSSL Project
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.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
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.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
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.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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.\" OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd $Mdocdate: November 16 2023 $
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.Dt EVP_SIGNINIT 3
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.Os
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.Sh NAME
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.Nm EVP_SignInit_ex ,
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.Nm EVP_SignUpdate ,
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.Nm EVP_SignFinal ,
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.Nm EVP_SignInit
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.Nd EVP signing functions
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.Sh SYNOPSIS
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.In openssl/evp.h
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.Ft int
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.Fo EVP_SignInit_ex
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.Fa "EVP_MD_CTX *ctx"
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.Fa "const EVP_MD *type"
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.Fa "ENGINE *impl"
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.Fc
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.Ft int
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.Fo EVP_SignUpdate
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.Fa "EVP_MD_CTX *ctx"
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.Fa "const void *d"
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.Fa "unsigned int cnt"
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.Fc
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.Ft int
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.Fo EVP_SignFinal
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.Fa "EVP_MD_CTX *ctx"
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.Fa "unsigned char *sig"
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.Fa "unsigned int *s"
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.Fa "EVP_PKEY *pkey"
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.Fc
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.Ft void
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.Fo EVP_SignInit
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.Fa "EVP_MD_CTX *ctx"
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.Fa "const EVP_MD *type"
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.Fc
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.Sh DESCRIPTION
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The EVP signature routines are a high level interface to digital
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signatures.
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.Pp
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.Fn EVP_SignInit_ex
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sets up a signing context
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.Fa ctx
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to use the digest
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.Fa type
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from
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.Vt ENGINE
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.Fa impl .
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.Fa ctx
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must be initialized with
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.Xr EVP_MD_CTX_init 3
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before calling this function.
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.Pp
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.Fn EVP_SignUpdate
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hashes
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.Fa cnt
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bytes of data at
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.Fa d
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into the signature context
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.Fa ctx .
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This function can be called several times on the same
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.Fa ctx
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to include additional data.
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.Pp
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.Fn EVP_SignFinal
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signs the data in
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.Fa ctx
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using the private key
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.Fa pkey
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and places the signature in
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.Fa sig .
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.Fa sig
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must be at least
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.Xr EVP_PKEY_size 3
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bytes in size.
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.Fa s
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is an OUT parameter, and not used as an IN parameter.
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The number of bytes of data written (i.e.\&
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the length of the signature) will be written to the integer at
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.Fa s .
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At most
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.Xr EVP_PKEY_size 3
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bytes will be written.
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.Pp
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.Fn EVP_SignInit
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initializes a signing context
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.Fa ctx
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to use the default implementation of digest
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.Fa type .
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.Pp
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The EVP interface to digital signatures should almost always be
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used in preference to the low level interfaces.
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This is because the code then becomes transparent to the algorithm used
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and much more flexible.
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.Pp
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The call to
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.Fn EVP_SignFinal
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internally finalizes a copy of the digest context.
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This means that calls to
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.Fn EVP_SignUpdate
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and
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.Fn EVP_SignFinal
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can be called later to digest and sign additional data.
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.Pp
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Since only a copy of the digest context is ever finalized, the context
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must be cleaned up after use by calling
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.Xr EVP_MD_CTX_free 3
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or a memory leak will occur.
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.Pp
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.Fn EVP_SignInit_ex ,
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.Fn EVP_SignUpdate ,
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and
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.Fn EVP_SignInit
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are implemented as macros.
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.Sh RETURN VALUES
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.Fn EVP_SignInit_ex ,
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.Fn EVP_SignUpdate ,
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and
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.Fn EVP_SignFinal
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return 1 for success and 0 for failure.
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.Pp
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The error codes can be obtained by
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.Xr ERR_get_error 3 .
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.Sh SEE ALSO
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.Xr evp 3 ,
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.Xr EVP_DigestInit 3 ,
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.Xr EVP_PKEY_asn1_set_public 3 ,
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.Xr EVP_PKEY_size 3 ,
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.Xr EVP_VerifyInit 3
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.Sh HISTORY
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.Fn EVP_SignInit ,
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.Fn EVP_SignUpdate ,
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and
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.Fn EVP_SignFinal
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first appeared in SSLeay 0.5.1 and have been available since
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.Ox 2.4 .
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.Pp
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.Fn EVP_SignInit_ex
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first appeared in OpenSSL 0.9.7 and has been available since
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.Ox 3.2 .
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.Sh BUGS
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Older versions of this documentation wrongly stated that calls to
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.Fn EVP_SignUpdate
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could not be made after calling
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.Fn EVP_SignFinal .
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.Pp
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Since the private key is passed in the call to
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.Fn EVP_SignFinal ,
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any error relating to the private key (for example an unsuitable key and
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digest combination) will not be indicated until after potentially large
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amounts of data have been passed through
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.Fn EVP_SignUpdate .
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.Pp
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It is not possible to change the signing parameters using these
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function.
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.Pp
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The previous two bugs are fixed in the newer EVP_DigestSign* function.
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