Abstract: Data synchronization is a basic rectuirement for authentication protocols and authenticated key exchange protocols, but it is much trickier and many times overlooked. By carefully analyzing an RFID authentication protocol, an RFID anthenticated key exchange protocol,and an authenticated key exchange protocol for mobile satellite communicalion systems which were found to be provably secure at present, attacks of data synchronization to these protocols were found respectively. These attacks destroy the availability of protocols. Furthermore, improvements to overcome the security vulnerabilities of these protocols were proposed.

Key words: Authentication protocol,Data synchronization,Attack,Security