.\"	$OpenBSD: BN_copy.3,v 1.10 2021/12/06 19:45:27 schwarze Exp $
.\"	OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100
.\"
.\" This file was written by Ulf Moeller <ulf@openssl.org>
.\" and Matt Caswell <matt@openssl.org>.
.\" Copyright (c) 2000, 2015 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: December 6 2021 $
.Dt BN_COPY 3
.Os
.Sh NAME
.Nm BN_copy ,
.Nm BN_dup ,
.Nm BN_with_flags
.Nd copy BIGNUMs
.Sh SYNOPSIS
.In openssl/bn.h
.Ft BIGNUM *
.Fo BN_copy
.Fa "BIGNUM *to"
.Fa "const BIGNUM *from"
.Fc
.Ft BIGNUM *
.Fo BN_dup
.Fa "const BIGNUM *from"
.Fc
.Ft void
.Fo BN_with_flags
.Fa "BIGNUM *dest"
.Fa "const BIGNUM *b"
.Fa "int flags"
.Fc
.Sh DESCRIPTION
.Fn BN_copy
copies
.Fa from
to
.Fa to .
.Pp
.Fn BN_dup
creates a new
.Vt BIGNUM
containing the value
.Fa from .
.Pp
.Fn BN_with_flags
creates a
.Em temporary
shallow copy of
.Fa b
in
.Fa dest .
It places significant restrictions on the copied data.
Applications that do not adhere to these restrictions
may encounter unexpected side effects or crashes.
For that reason, use of this function is discouraged.
.Pp
Any flags provided in
.Fa flags
will be set in
.Fa dest
in addition to any flags already set in
.Fa b .
For example, this can be used to create a temporary copy of a
.Vt BIGNUM
with the
.Dv BN_FLG_CONSTTIME
flag set for constant time operations.
.Pp
The temporary copy in
.Fa dest
will share some internal state with
.Fa b .
For this reason, the following restrictions apply to the use of
.Fa dest :
.Bl -bullet
.It
.Fa dest
should be a newly allocated
.Vt BIGNUM
obtained via a call to
.Xr BN_new 3 .
It should not have been used for other purposes or initialised in any way.
.It
.Fa dest
must only be used in "read-only" operations, i.e. typically those
functions where the relevant parameter is declared "const".
.It
.Fa dest
must be used and freed before any further subsequent use of
.Fa b .
.El
.Sh RETURN VALUES
.Fn BN_copy
returns
.Fa to
on success or
.Dv NULL
on error.
.Fn BN_dup
returns the new
.Vt BIGNUM
or
.Dv NULL
on error.
The error codes can be obtained by
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr BN_new 3 ,
.Xr BN_set_flags 3
.Sh HISTORY
.Fn BN_copy
and
.Fn BN_dup
first appeared in SSLeay 0.5.1 and have been available since
.Ox 2.4 .
.Pp
.Fn BN_with_flags
first appeared in OpenSSL 0.9.7h and 0.9.8a
and has been available since
.Ox 4.0 .