xref: /openssl/doc/man3/BN_copy.pod (revision 4746f25a)
1=pod
2
3=head1 NAME
4
5BN_copy, BN_dup, BN_with_flags - copy BIGNUMs
6
7=head1 SYNOPSIS
8
9 #include <openssl/bn.h>
10
11 BIGNUM *BN_copy(BIGNUM *to, const BIGNUM *from);
12
13 BIGNUM *BN_dup(const BIGNUM *from);
14
15 void BN_with_flags(BIGNUM *dest, const BIGNUM *b, int flags);
16
17=head1 DESCRIPTION
18
19BN_copy() copies B<from> to B<to>. BN_dup() creates a new B<BIGNUM>
20containing the value B<from>.
21
22BN_with_flags creates a B<temporary> shallow copy of B<b> in B<dest>. It places
23significant restrictions on the copied data. Applications that do no adhere to
24these restrictions may encounter unexpected side effects or crashes. For that
25reason use of this function is discouraged. Any flags provided in B<flags> will
26be set in B<dest> in addition to any flags already set in B<b>. For example this
27might commonly be used to create a temporary copy of a BIGNUM with the
28B<BN_FLG_CONSTTIME> flag set for constant time operations. The temporary copy in
29B<dest> will share some internal state with B<b>. For this reason the following
30restrictions apply to the use of B<dest>:
31
32=over 2
33
34=item *
35
36B<dest> should be a newly allocated BIGNUM obtained via a call to BN_new(). It
37should not have been used for other purposes or initialised in any way.
38
39=item *
40
41B<dest> must only be used in "read-only" operations, i.e. typically those
42functions where the relevant parameter is declared "const".
43
44=item *
45
46B<dest> must be used and freed before any further subsequent use of B<b>
47
48=back
49
50=head1 RETURN VALUES
51
52BN_copy() returns B<to> on success, NULL on error. BN_dup() returns
53the new B<BIGNUM>, and NULL on error. The error codes can be obtained
54by L<ERR_get_error(3)>.
55
56=head1 SEE ALSO
57
58L<ERR_get_error(3)>
59
60=head1 COPYRIGHT
61
62Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.
63
64Licensed under the Apache License 2.0 (the "License").  You may not use
65this file except in compliance with the License.  You can obtain a copy
66in the file LICENSE in the source distribution or at
67L<https://www.openssl.org/source/license.html>.
68
69=cut
70