When we consider user's convenience for electronic transactions, it might be desirable to generate a digital signature using biometrics. However, it is not easy nor practicable in today's communications environment because of inaccurate measuring and potential hill-climbing attacks with regard to biometrics, unless specific hardware storage is provided for manipulating signature keys or biometric templates securely. In this paper, we study a simple practical method for biometrics based digital signature generation without such restriction. It is based on the existing tools in software in our proposed model where a general digital signature such as RSA can be applied without losing its security. This is not a cryptography paper but rather written from the practical perspectives.