=pod

=head1 NAME

BN_CTX_new_ex, BN_CTX_new, BN_CTX_secure_new_ex, BN_CTX_secure_new, BN_CTX_free
- allocate and free BN_CTX structures

=head1 SYNOPSIS

 #include <openssl/bn.h>

 BN_CTX *BN_CTX_new_ex(OSSL_LIB_CTX *ctx);
 BN_CTX *BN_CTX_new(void);

 BN_CTX *BN_CTX_secure_new_ex(OSSL_LIB_CTX *ctx);
 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_ex() allocates and initializes a B<BN_CTX> structure for the given
library context B<ctx>. The <ctx> value may be NULL in which case the default
library context will be used. BN_CTX_new() is the same as BN_CTX_new_ex() except
that the default library context is always used.

BN_CTX_secure_new_ex() 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 for the given library context B<ctx>. The <ctx> value may be NULL in
which case the default library context will be used. BN_CTX_secure_new() is the
same as BN_CTX_secure_new_ex() except that the default library context is always
used.

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 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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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