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(3)) in order to save the overhead of repeatedly creating and freeing BIGNUM s 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 BIGNUM s. 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. If ctx is NULL, nothing is done. 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(3).




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