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.\" $OpenBSD: EVP_OpenInit.3,v 1.5 2016/11/26 20:55:26 schwarze Exp $
.\" OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
.\"
.\" This file was written by Dr. Stephen Henson <steve@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,
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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.\"
.Dd $Mdocdate: November 26 2016 $
.Dt EVP_OPENINIT 3
.Os
.Sh NAME
.Nm EVP_OpenInit ,
.Nm EVP_OpenUpdate ,
.Nm EVP_OpenFinal
.Nd EVP envelope decryption
.Sh SYNOPSIS
.In openssl/evp.h
.Ft int
.Fo EVP_OpenInit
.Fa "EVP_CIPHER_CTX *ctx"
.Fa "EVP_CIPHER *type"
.Fa "unsigned char *ek"
.Fa "int ekl"
.Fa "unsigned char *iv"
.Fa "EVP_PKEY *priv"
.Fc
.Ft int
.Fo EVP_OpenUpdate
.Fa "EVP_CIPHER_CTX *ctx"
.Fa "unsigned char *out"
.Fa "int *outl"
.Fa "unsigned char *in"
.Fa "int inl"
.Fc
.Ft int
.Fo EVP_OpenFinal
.Fa "EVP_CIPHER_CTX *ctx"
.Fa "unsigned char *out"
.Fa "int *outl"
.Fc
.Sh DESCRIPTION
The EVP envelope routines are a high level interface to envelope
decryption.
They decrypt a public key encrypted symmetric key and then decrypt data
using it.
.Pp
.Fn EVP_OpenInit
initializes a cipher context
.Fa ctx
for decryption with cipher
.Fa type .
It decrypts the encrypted symmetric key of length
.Fa ekl
bytes passed in the
.Fa ek
parameter using the private key
.Fa priv .
The IV is supplied in the
.Fa iv
parameter.
.Pp
.Fn EVP_OpenUpdate
and
.Fn EVP_OpenFinal
have exactly the same properties as the
.Xr EVP_DecryptUpdate 3
and
.Xr EVP_DecryptFinal 3
routines.
.Pp
It is possible to call
.Fn EVP_OpenInit
twice in the same way as
.Xr EVP_DecryptInit 3 .
The first call should have
.Fa priv
set to
.Dv NULL
and (after setting any cipher parameters) it should be
called again with
.Fa type
set to
.Dv NULL .
.Pp
If the cipher passed in the
.Fa type
parameter is a variable length cipher then the key length will be set to
the value of the recovered key length.
If the cipher is a fixed length cipher then the recovered key length
must match the fixed cipher length.
.Sh RETURN VALUES
.Fn EVP_OpenInit
returns 0 on error or a non-zero integer (actually the recovered secret
key size) if successful.
.Pp
.Fn EVP_OpenUpdate
returns 1 for success or 0 for failure.
.Pp
.Fn EVP_OpenFinal
returns 0 if the decrypt failed or 1 for success.
.Sh SEE ALSO
.Xr evp 3 ,
.Xr EVP_EncryptInit 3 ,
.Xr EVP_SealInit 3 ,
.Xr RAND_bytes 3
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