What started as a theoretical question ("What does it mean to sign streaming content over the Web?") has evolved into one of the most interesting and practice-oriented group research project.
The problem of signing digital streams to prove their authenticity is substantially different from the problem of signing regular messages. Traditional signature schemes are message oriented and require the receiver to process the entire message before being able to authenticate its signature. However, a stream is a potentially very long ( or infinite) sequence of bits that the sender sends to the receiver and the receiver is required to consumes the received bits at more or less the input rate and without excessive delay. Therefore it is infeasible for the receiver to obtain the entire stream before authenticating and consuming it. Examples of streams include digitized video and audio files, data feeds and applets.
Members of the group devised efficient solutions for the problem of non-repudiable authentication of digital streams. The initial solutions were then optimized and adapted to the problem of Secure Multicast : Efficient authentication of source and data in a group communication setting where other group members are not trusted, and key management in groups with dynamic membership. And now group members are leading efforts in the development and standardization of protocols for secure multicast (see the secure multicast working group of the IRTF SMuG and the MSEC working group of the IETF).
R.Gennaro and P.Rohatgi. How to Sign Digital Streams. Information and Computation 165(1), pp.100-116 (2001). A preliminary version appears in the proceedings of CRYPTO'97, Springer-Verlag, LNCS 1294, pp.180-197.
A.Perrig, R.Canetti, D.Tygar and D.Song. Efficient and Secure Source Authentication for Multicast. Proceedings of the Network and Distributed System Security Symposium (NDSS2001), Feb 2001.
R.Canetti and B.Pinkas. A taxonomy of multicast security issues. Internet Draft.
A.Perrig, R.Canetti, D.Tygar and D.Song. Efficient Authentication and Signature of Multicast Streams over Lossy Channels. Proceedings of the 2000 IEEE Symposium on Security and Privacy.
R.Canetti, P-C.Cheng, F.Giraud, D.Pendarakis, J.R.Rao, P.Rohatgi and D. Saha. IPSec-based Host Architecture for Secure Internet Multicast. Proceedings of Network and Distributed System Security Symposium (NDSS2000), Feb 2000.
R. Canetti, J. Garay, G. Itkis, D. Micciancio, M. Naor and B. Pinkas, A taxonomy of multicast security issues and efficient constructions. Proceedings of Infocom'99.