BN_CTX_start, BN_CTX_get, BN_CTX_end - Use temporary BIGNUM variables
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 the BN_CTX_new() function) 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
Finally, BN_CTX_end() must be called before returning from the func‐
tion. When BN_CTX_end() is called, the BIGNUM pointers obtained from
BN_CTX_get() become invalid.
The BN_CTX_start() and BN_CTX_end() functions return no values.
The BN_CTX_get() function 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().
The BN_CTX_start(), BN_CTX_get(), and BN_CTX_end() functions were added
in OpenSSL 0.9.5.