High Performance, Robust and Secure Group Communication

Quarterly Technical Report, October 2001

Progress:

• BD (Burmester Desmedt) - a protocol that requires three rounds and upto n multicasts in each round, and is fairly easy to make it robust.
• CKD (Centralized Key Distribution) - a protocol that selects a leader based on the membership of a group and that leader computes a key and disseminates it to the others.
• GDH (Group Diffie Hellman) - our basic CLIQUES protocol.
• STR - A sparse tree group Diffie Hellman.
• TGDH (Tree-based Group Diffie Hellman).

We have experimented with the five different protocols over a local area network.

We completed an initial implementation of our access control framework which is part of our integrated architecture. This framework specifies a modular architecture allowing multiple access control and authentication protocols to be used and the location of checks in the group communication system to enforce the policies. The access control and authentication framework adds two new features to the Spread group communication system. First, it provides a modular API that allows anyone to write a custom authentication and access control policy code module which will be loaded into the Spread daemon. This module (or modules) will control how clients are authenticated when they connect to the daemon and what restrictions should be enforced on the clients actions (such as joining groups or sending messages). Second, it inserts appropriate checks into Spread to enforce whatever access control policy the user has enabled.

We have made a major step forward in the design of our integrated architecture with respect to the key management building block. In the integrated architecture, this building block is moved from the Secure Spread library to the Spread daemon itself. The Spread daemons share a key and based on it and additional information generate group keys and refresh them after every group membership change. The daemons key is changed upon daemon membership changes. We have devised three types of solutions to obtain a shared daemon key, depending on where and how encryption is done and what group communication model is used:

• Virtual Synchrony solution: provides the client with a Virtual Synchrony model, similar to the current layered Secure Spread implementation. It has the advantage, compared with the layered architecture, that key agreement protocol is required on every network connectivity change and not every join and leave of a client. Client joins and leave only require a local computation at each of the daemons that have relevant clients.
• Extended Virtual Synchrony solution: provides the client with the more efficient Extended Virtual Synchrony model. We are protecting the data between the client and the daemon using a client-daemon key that is generated upon connect. The drawback of this method is that every message will be encrypted three times and deciphered three time (client -> daemon) (daemon -> daemons) (daemon -> client).
• Optimized Extended Virtual Synchrony solution: similar to the above but in most cases encrypt and decipher the message only once. Only in messages that are sent just before a daemon connectivity change there will be a need for the messages to be deciphered and re-encrypted by the daemons. This solution provides a considerable performance boost, but is fairly complex to implement.

We were fortunate to host the Program Manager Dr. Douglas Maughan during this period. During the visit we demonstrated the Secure Spread system in action and live nation-wide experiments with Spread.

Software:

Technology Transfer:

We are starting to get some comments from the community regarding issues with the Secure Spread release, which means that at least some people are exploring it.

Plans for Next Quarter:

• Experiment with the key agreement protocols supported by our framework on wide area networks. Continue to explore the different trade-offs of the different key agreement protocols as they manifest themselves on local and wide area networks.
• Continue our work on the integrated architecture.
• Update the integrated access control and authentication framework based on community feedback.
• Continued research into high performance wide area group communication.