.\"	$OpenBSD: BN_copy.3,v 1.9 2018/03/27 17:35:50 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>.
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.Dd $Mdocdate: March 27 2018 $
.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 macro 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 .