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

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       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>.

3.5.0                                              2025-06-04                                   BN_CTX_NEW(3SSL)

       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.

BN_CTX_init() was removed in OpenSSL 1.1.0.

       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

        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);

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.

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

        #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);