BN_CTX_new(3) | OpenSSL | BN_CTX_new(3)

# 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

# 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);

# DESCRIPTION

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

BN_CTX_new_ex() allocates and initializes a BN_CTX structure for the given library context 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 BN_CTX structure but uses the secure heap (see CRYPTO_secure_malloc(3)) to hold the BIGNUMs for the given library context 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 BN_CTX and the structure itself. Since BN_CTX_start() is required in order to obtain BIGNUMs from the BN_CTX, in most cases BN_CTX_end() must be called before the BN_CTX may be freed by BN_CTX_free(). If c is NULL, nothing is done.

A given 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.

# RETURN VALUES

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

BN_CTX_free() has no return values.

# 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);

# SEE ALSO

ERR_get_error(3), BN_add(3), BN_CTX_start(3)

# HISTORY

BN_CTX_init() was removed in OpenSSL 1.1.0.

# 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 <https://www.openssl.org/source/license.html>.

2026-06-09 | 3.5.7