=pod

=head1 NAME

BN_CTX_new, BN_CTX_secure_new, BN_CTX_free - allocate and free BN_CTX structures

=head1 SYNOPSIS

 #include <openssl/bn.h>

 BN_CTX *BN_CTX_new(void);

 BN_CTX *BN_CTX_secure_new(void);

 void BN_CTX_free(BN_CTX *c);

=head1 DESCRIPTION

A B<BN_CTX> is a structure that holds B<BIGNUM> temporary variables used by
library functions. Since dynamic memory allocation to create B<BIGNUM>s
is rather expensive when used in conjunction with repeated subroutine
calls, the B<BN_CTX> structure is used.

BN_CTX_new() allocates and initializes a B<BN_CTX> structure.
BN_CTX_secure_new() allocates and initializes a B<BN_CTX> structure
but uses the secure heap (see L<CRYPTO_secure_malloc(3)>) to hold the
B<BIGNUM>s.

BN_CTX_free() frees the components of the B<BN_CTX> and the structure itself.
Since BN_CTX_start() is required in order to obtain B<BIGNUM>s from the
B<BN_CTX>, in most cases BN_CTX_end() must be called before the B<BN_CTX> may
be freed by BN_CTX_free().  If B<c> is NULL, nothing is done.

A given B<BN_CTX> must only be used by a single thread of execution.  No
locking is performed, and the internal pool allocator will not properly handle
multiple threads of execution.

=head1 RETURN VALUES

BN_CTX_new() and BN_CTX_secure_new() return a pointer to the B<BN_CTX>.
If the allocation fails,
they return B<NULL> and sets an error code that can be obtained by
L<ERR_get_error(3)>.

BN_CTX_free() has no return values.

=head1 REMOVED FUNCTIONALITY

 void BN_CTX_init(BN_CTX *c);

BN_CTX_init() is no longer available as of OpenSSL 1.1.0. Applications should
replace use of BN_CTX_init with BN_CTX_new instead:

 BN_CTX *ctx;
 ctx = BN_CTX_new();
 if (!ctx)
     /* error */
 ...
 BN_CTX_free(ctx);

=head1 SEE ALSO

L<ERR_get_error(3)>, L<BN_add(3)>,
L<BN_CTX_start(3)>

=head1 HISTORY

BN_CTX_init() was removed in OpenSSL 1.1.0.

=head1 COPYRIGHT

Copyright 2000-2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

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