ABSTRACT
Security protocol is also known cryptographic protocols. It is messaging protocol based on Cryptography, and it achieved the purposes of assign passwords and authentication by means of cryptographic algorithms. Authentication protocol is also an important part of the security protocol, and its main functions include authentication, key distribution, and non-repudiation of messages. The most famous authentication protocol is the Needham-Schroeder protocol and it is mainly divided into NSSK protocols and NSPK protocols. NSSK agreements have a significant impact on the design and verification of later authentication protocol. The most famous attack to NSSK agreement is Denning-Sacco. Denning and Sacco think the main security problem of NSSK is that the agreement responder B could not determine the freshness of messages 3. Many scholars have made some crack programs and improved protocol, for example, reference (Liao et al. 2009) proposed an improved NSSK protocol. This article use formal verification tools to verify the feasibility of the protocol in reference (Liao et al. 2009), and proposed another improved NSSK protocol.
