190 lines
5.8 KiB
Groff
190 lines
5.8 KiB
Groff
.\" $OpenBSD: EVP_PKEY_verify_recover.3,v 1.9 2018/03/23 04:34:23 schwarze Exp $
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.\" full merge up to: OpenSSL 48e5119a Jan 19 10:49:22 2018 +0100
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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) 2006, 2009, 2010, 2013, 2018 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: March 23 2018 $
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.Dt EVP_PKEY_VERIFY_RECOVER 3
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.Os
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.Sh NAME
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.Nm EVP_PKEY_verify_recover_init ,
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.Nm EVP_PKEY_verify_recover
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.Nd recover signature using a public key algorithm
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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_PKEY_verify_recover_init
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.Fa "EVP_PKEY_CTX *ctx"
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.Fc
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.Ft int
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.Fo EVP_PKEY_verify_recover
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.Fa "EVP_PKEY_CTX *ctx"
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.Fa "unsigned char *rout"
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.Fa "size_t *routlen"
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.Fa "const unsigned char *sig"
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.Fa "size_t siglen"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn EVP_PKEY_verify_recover_init
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function initializes a public key algorithm context using key
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.Fa ctx->pkey
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for a verify recover operation.
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.Pp
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The
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.Fn EVP_PKEY_verify_recover
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function recovers signed data using
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.Fa ctx .
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The signature is specified using the
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.Fa sig
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and
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.Fa siglen
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parameters.
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If
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.Fa rout
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is
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.Dv NULL ,
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then the maximum size of the output buffer is written to the
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.Fa routlen
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parameter.
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If
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.Fa rout
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is not
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.Dv NULL ,
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then before the call the
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.Fa routlen
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parameter should contain the length of the
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.Fa rout
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buffer.
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If the call is successful, recovered data is written to
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.Fa rout
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and the amount of data written to
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.Fa routlen .
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.Pp
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Normally an application is only interested in whether a signature
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verification operation is successful.
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In those cases, the
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.Xr EVP_PKEY_verify 3
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function should be used.
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.Pp
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Sometimes however it is useful to obtain the data originally signed
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using a signing operation.
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Only certain public key algorithms can recover a signature in this way
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(for example RSA in PKCS padding mode).
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.Pp
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After the call to
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.Fn EVP_PKEY_verify_recover_init ,
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algorithm specific control operations can be performed to set any
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appropriate parameters for the operation.
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.Pp
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The function
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.Fn EVP_PKEY_verify_recover
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can be called more than once on the same context if several operations
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are performed using the same parameters.
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.Sh RETURN VALUES
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.Fn EVP_PKEY_verify_recover_init
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and
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.Fn EVP_PKEY_verify_recover
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return 1 for success and 0 or a negative value for failure.
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In particular, a return value of -2 indicates the operation is not
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supported by the public key algorithm.
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.Sh EXAMPLES
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Recover digest originally signed using PKCS#1 and SHA256 digest:
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.Bd -literal -offset indent
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#include <openssl/evp.h>
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#include <openssl/rsa.h>
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EVP_PKEY_CTX *ctx;
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unsigned char *rout, *sig;
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size_t routlen, siglen;
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EVP_PKEY *verify_key;
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/*
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* Assumes that verify_key, sig, and siglen are already set up
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* and that verify_key is an RSA public key.
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*/
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ctx = EVP_PKEY_CTX_new(verify_key, NULL);
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if (!ctx)
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/* Error occurred */
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if (EVP_PKEY_verify_recover_init(ctx) <= 0)
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/* Error */
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if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
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/* Error */
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if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
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/* Error */
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/* Determine buffer length */
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if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
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/* Error */
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rout = malloc(routlen);
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if (!rout)
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/* malloc failure */
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if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
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/* Error */
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/* Recovered data is routlen bytes written to buffer rout */
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.Ed
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.Sh SEE ALSO
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.Xr EVP_PKEY_CTX_new 3 ,
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.Xr EVP_PKEY_decrypt 3 ,
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.Xr EVP_PKEY_derive 3 ,
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.Xr EVP_PKEY_encrypt 3 ,
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.Xr EVP_PKEY_meth_set_verify_recover 3 ,
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.Xr EVP_PKEY_sign 3 ,
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.Xr EVP_PKEY_verify 3
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.Sh HISTORY
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.Fn EVP_PKEY_verify_recover_init
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and
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.Fn EVP_PKEY_verify_recover
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first appeared in OpenSSL 1.0.0 and have been available since
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.Ox 4.9 .
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