Tel-Aviv University - Computer Science Colloquium
Sunday, April 11, 14:15-15:15
at 14:00 The basic setting of this talk concerns a service provider that needs to communicate securely with a set of users over an insecure broadcast channel. This problem naturally occurs in the satellite/cable pay TV industry. In such an environment, users have set top terminals (STTs), which perform the cryptographic functions. The secure storage of the STTs is severely limited due to the need to withstand pirate attacks and hardware tampering.
The first topic I will discuss deals with allocating establishment keys to users' STTs, assuming only uni-directional communication. Our approach is to allow a controlled number of non-paying customers to occasionally receive the multicast, and by this to break away from some known theoretical bounds. Our results indicate that, unlike previous solutions, we can design practical schemes in this setting.
Then I will discuss the problem of tracking the location of newer STTs, which also have an uplink capability. Service providers would like to prevent customers from moving an STT from, e.g., a home to a bar. We studied four schemes, which are based on existing or emerging technologies: Caller-ID; GPS; cellular enhanced 911; and satellite ranging. I will discuss the accuracy, features and vulnerabilities of the schemes, and possible attacks that allow pirates to conceal their movement when these schemes are used.
Finally, I will touch upon key management for periodic (e.g., monthly) keys. The number of encrypted TV programs in a billing period may be very large. Nevertheless, the service provider would like to offer different packages of programs to the users, from small, single-program packages, up to huge, all-programs packages. A user who buys the keys for a package should be able to view every program belonging to that package, but nothing else. I will discuss several schemes that achieve these goals.
This talk is based on joint work with Michel Abdalla, Eran Gabber, and Yuval Shavitt.
For colloquium schedule, see http://www.math.tau.ac.il/~matias/colloq.html