Securely Measuring Peer Contribution in LiveShift

LiveShift is a P2P video streaming application developed by the CSG group at the University of Zurich. The application supports both live streaming and video-on-demand in an integrated manner. While video is transmitted through the P2P network in a live fashion, all peers participate in distributed storage. This adds the ability to replay time-shifted streams from other peers in a distributed and scalable manner.

In order to improve scalability and fairness in LiveShift, the overlay must be organized in a way that peers with higher upload capacity are given preference to receive blocks. The effect is multi-fold: at the same time it punishes free-riders and rewards good contributors, while reducing average peer distance to the peercaster.

The problem is that the upload capacity is not easily securely measured by other peers in the system. Tit-for-tat (TFT) as used in BitTorrent requires symmetry of interest, which cannot be taken for granted in LiveShift. Reports from those peers or third parties should not be simply trusted, due to the risk posed by lying peers, colluders, and Sybil attacks.

The main goal of this thesis is to extend LiveShift protocol by adding a secure contribution-awareness mechanism. Final results are to be assessed using experiments using LiveShift.