Paper review: Reliable Group Rekeying: A Performance Analysis

Reviewer: Mike Liu

1. State the problem the paper is trying to solve.
The main problem the paper is trying to solve is the scalability issues of reliable group rekey.
2. State the main contribution of the paper: solving a new problem, proposing a new algorithm, or presenting a new evaluation (analysis). If a new problem, why was the problem important? Is the problem still important today? Will the problem be important tomorrow?  If a new algorithm or new evaluation (analysis), what are the improvements over previous algorithms or evaluations? How do they come up with the new algorithm or evaluation? 
The main contribution of this paper is that it proposes a new scheme for group rekey that is scalable, reliable, and alleviates out-of-sync problems. The problem will become more and more important today and in the future as the number of network application, such a pay-per-view distribution of digital media, restricted teleconferences, and pay-per-use multi-party games, are increased.
3. Summarize the (at most) 3 key main ideas (each in 1 sentence.) 
The three 3 key main ideas are: (1) The authors have developed a new scheme for reliable group rekeying that is based on key trees and uses periodic batch rekeying to improve scalability, alleviates out-of-sync problems among rekey messages, and acheives large performance gains. (2) They observe that rekey transport has an eventual reliability and a soft real-time requirement, and that the rekey workload has a sparseness property, that is each each group user only needs to receive a small fraction of the packets that carry a rekey message sent by the key server. (3) The authors then present a reliable rekey transport protocol based on proactive FEC, show the tradeoffs between bandwidth requirements and rekey interval, and then provide four system constraints that serve as guidelines for choosing an appropriate rekey interval and determining the maximum nuber of users a key server can support.
4. Critique the main contribution
   • Rate the significance of the paper on a scale of 5 (breakthrough), 4 (significant contribution), 3 (modest contribution), 2 (incremental contribution), 1 (no contribution or negative contribution). Explain your rating in a sentence or two.
   I give this paper a rating of 4 because it presents a great scheme for achieving a scalable group rekey system that will be the groundwork for making network applications both secure and financially workable.
   • Rate how convincing the methodology is: how do the authors justify the solution approach or evaluation? Do the authors use arguments, analyses, experiments, simulations, or a combination of them? Do the claims and conclusions follow from the arguments, analyses or experiments? Are the assumptions realistic (at the time of the research)? Are the assumptions still valid today? Are the experiments well designed? Are there different experiments that would be more convincing? Are there other alternatives the authors should have considered? (And, of course, is the paper free of methodological errors.)
   The authors' methodology was to present an analytical approach for why their group rekeying system does not suffer from problems with scalability and reliablity, and then they offer initial simulations done with an implementation of their group rekeying system as a protocol.
   • What is the most important limitation of the approach?
   Though their simulation results were very close to their analytical results, that is because the simulations were not done with very detailed traces. In order for their system to be fully considered for full Internet use, it would be best to run a more detailed trace based experimental evaluation to prove that they system will indeed by robustly scalable and reliable even in the midst of the very dynamic and intolerant behavior of the real Intenet. Even so, the closeness of their analytical results with their less detailed simulation results gives great hope that the same results will be obtained with tests done for my detailed traces.
5. What lessons should researchers and builders take away from this work. What (if any) questions does this work leave open?
The lessons that researchers should take away from this work are that it is now possible to build a scalable and reliable group rekeying system and the secret currently lies in periodic batch rekeying, which is responsible for most of the large performance and scalability gains. Future work spurred by this paper include investigations of dynamic partitioning of group users, more detailed trace based experimental evaluations, and investigations of FEC encoding schemes that work better for a workload with the sparseness property. an efficient, scalable, and implementable system for IP traceback and it has been done despite the seeminly large memory requirements. The potential memory requirent roadblock can be overcome using Bloom Filters and this system can continue to be effective for tracing packets, even those that undergo transformations.