Scalable key distribution for secure multicast

This report presents and analyzes possible solutions for key distribution in a multicast group. Unlike, two-party security that is a well studied field, multiparty communications offer some interesting problems open for research. For key distribution in a multicast group, the biggest problem we have holds in one word : scalability. Scalable multicast protocols call for a security scheme that avoids the sharing of secret keying material among the recipients. In the proposed model the source transmits a unique message on the multicast tree but each recipient or sub-group of recipients uses different keying material to get accross the protected multicast channel. We suggest several protocols based on extensions of classical cryptographic functions. The first one is a simple XOR scheme and the two other schemes are based respectively on ElGamal and RSA.