Design of Secure Key Establishment Protocols: Successes, Failures and Prospects

Mounita Saha, Dipanwita RoyChowdhury

The design of a secure and efficient key establishment protocol is one of the toughest challenge in communication protocol design. In the literature many key establishment protocols claimed to be secure against some attacks were later shown to be weak against new attacks. In this work, we have identified a class of weakness named as insider-replay in some existing protocols and proposed a design principle to avoid the weakness. Based on the design principle, we have proposed an efficient key establishment protocol. The proposed protocol is shown to be provably secure under formal security model and averts insider-replay. We have also analyzed the efficiency of the proposed protocol in comparison with existing protocols.

Colin Boyd

Junghyun Nam

Key establishment protocols are fundamental for establishing secure communication channels over public insecure networks.Security must be given the topmost priority in the design of a key establishment protocol.In this work, we provide a security analysis on two recent key establishment protocols: Harn and Lin's group key transfer protocol and Dutta and Barua's group key agreement protocol.Our analysis shows that both the Harn-Lin protocol and the Dutta-Barua protocol have a flaw in their design and can be easily attacked.The attack we mount on the Harn-Lin protocol is a replay attack whereby a malicious user can obtain the long-term secrets of any other users.The Dutta-Barua protocol is vulnerable to an unknown key-share attack.For each of the two protocols, we present how to eliminate their security vulnerabilities.We also improve Dutta and Barua's proof of security to make it valid against unknown key share attacks.

Carsten Rudolph

Chih-Hung Li

For a secure communication through the public network, cryptographic encryption must be applied. The key establishment issue is the most important part in cryptographic encryption. Only the legitimate principals who have the key can encrypt messages and decrypt cryptograms. A secure multi-party communication held through the public network can only take place after a multi-party key establishment protocol has been executed. The multi-party key establishment protocol is designed so that the principals can receive a common key and use it to securely exchange the messages.\nIn this thesis, the secure multi-party key establishment protocols are discussed. W e start from investigating properties of two-party key establishment protocols such as motivation of using session key, adversaries in the protocols, attacks of the protocol and security analysis of the protocol. Then we give the requirements of a multi-party key establishment protocol and summarize about what should be considered in designing a multi-party key establishment protocol. After that we review some of the previous proposed multi-party key establishment protocol. The existing multi-party key establishment protocols are either impractical ( not efficient enough) or missing some important security goals such as authentication of principals. Three new protocols are proposed in this thesis. The first protocol addresses how to hold a conference for members of two hierarchical groups in an efficient way. The message broadcasting is used to reduce the cost of secure message transport.\nThe second and the third protocols manage the authentication problem by using a secret sharing scheme. We replace the principal authentication with the group authentication so that the computational overhead and communication overhead will be reduced especially in reuse of the protocol for new communication. Again, message broadcasting is used for replacing the expansive secure communication channel.\nPart of this thesis appeared in ACSC'99(Australian Computer Science Conference) and ACISP'99(Australian Conference of Information Security and Privacy).

Colin Boyd, Anish Mathuria