Cryptography and SSL/TLS Toolkit



BN_CTX_start, BN_CTX_get, BN_CTX_end - use temporary BIGNUM variables


 #include <openssl/bn.h>

 void BN_CTX_start(BN_CTX *ctx);

 BIGNUM *BN_CTX_get(BN_CTX *ctx);

 void BN_CTX_end(BN_CTX *ctx);


These functions are used to obtain temporary BIGNUM variables from a BN_CTX (which can been created by using BN_CTX_new) in order to save the overhead of repeatedly creating and freeing BIGNUMs in functions that are called from inside a loop.

A function must call BN_CTX_start() first. Then, BN_CTX_get() may be called repeatedly to obtain temporary BIGNUMs. All BN_CTX_get() calls must be made before calling any other functions that use the ctx as an argument.

Finally, BN_CTX_end() must be called before returning from the function. When BN_CTX_end() is called, the BIGNUM pointers obtained from BN_CTX_get() become invalid.


BN_CTX_start() and BN_CTX_end() return no values.

BN_CTX_get() returns a pointer to the BIGNUM, or NULL on error. Once BN_CTX_get() has failed, the subsequent calls will return NULL as well, so it is sufficient to check the return value of the last BN_CTX_get() call. In case of an error, an error code is set, which can be obtained by ERR_get_error.



Copyright 2000-2016 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