Abstract: Protecting software codes from illegal tampers is a severe problem for software developers. Based on the idea of guards, this paper proposes a cycling guards model which can protect the integrity of the program with more flexible way. All the guards form cycle chain to ensure that each guard is protected by other guards, to protect the integrity of the software itself, at the same time ensuring the security of guards. Meanwhile, the paper proposes a protocol of data integrity check to check integrity of checking guards real-time and proves the protocol’s security.

Key words: software protection, integrity checking, guard, cyclical guard