1. Secure Group Communication Shaun Jamieson Shawn Smith John Stephens William Heinbockel

2. Agenda ● Brief Review of Protocol ● Overview of Implementation ● Encryption Algorithm ● Challenges ● Future Work ● Demonstration

3. Protocol ● Actions – Join – Leave – Merge – Partition ● Group Key – Generated from a binary tree

4. Implementation ● Join – Join to an individual's nickname/unihandle – That unihandle becomes the “session sponsor” – Session sponsor remains sponsor until sponsorship is taken from them – Adds client to tree, rebroadcasts – Individual clients use new tree to regenerate group key

5. Implementation (continued) ● Leave – Contact current sponsor – Sponsor updates tree and rebroadcasts – Clients regenerate group key based on new tree ● Group formation – Initially initiate a join request with yourself ● Synchronization – Before a sponsor processes a join, they make sure they are the only active sponsor

6. Encryption Algorithm ● ElGamel algorithm – depends on a seperate session key pair for each transmission – session public key is transmitted and the session private key is thrown away ● Key-Pair Generation – Key pairs are generated using the Diffie-Hellman algorithm by starting off with a random private key. (we use a random 128-bit private key).

7. Encryption Algorithm (continued) ● Key-Pair Generation (continued) – the algorithm for encryption is similar to the format for Diffie-Hellman: ( data * ( public key ) ^ ( session private ) ) mod p ● Notes – Since we use a single pair of session keys for each transmission, this makes our encryption fundamentally weak. The encryption can be broken by simply guessing what character is mapped to the given number. A better implementation would encrypt each byte with a new key pair, making that form of guessing much harder.

8. Challenges ● Ad-Hoc Problems – Depends on lower gree nodes not knowing keys of other lower nodes ● Implementation Limitations – Assumption of security in M2MI (cannot forge multi/unihandles) – Currently must know unihandle to join to – Somewhat high overhead

9. Future Work ● Actions to add – Partition – Merge ● Join by group or unihandle ● Effeciency Refinements

10. Demonstration