Abstract: Studied a strong password authentication protocol based on hash function, by analyzing the security of SPAS protocol among this kind of protocols. Although the SPAS is designed meticulously and regarded as more secure, but we also find some secure vulnerability in it. Using single cryptography technology induces this protocol has secure leak. At last we can prove that if this kind of protocol uses single cryptography technology, it can't produce a secure protocol.

Key words: Hash function, Authentication protocol, Strong password authentication protocol