RSA_new() allocates and initializes an RSA structure. It is equivalent to calling RSA_new_method(NULL).
RSA_free() frees the RSA structure and its components. The key is erased before the memory is returned to the system.
If the allocation fails, RSA_new() returns NULL and sets an error code that can be obtained by ERR_get_error(3). Otherwise it returns a pointer to the newly allocated structure.
RSA_free() returns no value.