+B<BIGNUM>s for the given library context B<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 B<BN_CTX> and the structure itself.
+Since BN_CTX_start() is required in order to obtain B<BIGNUM>s from the
+B<BN_CTX>, in most cases BN_CTX_end() must be called before the B<BN_CTX> may
+be freed by BN_CTX_free(). If B<c> is NULL, nothing is done.