Local View Attack on Anonymous Communication
We consider anonymous communication protocols based on onions: each message is sent in an encrypted form through a path chosen at random by its sender, and the message is re-coded by each server on the path. Recently, it has been shown that if the anonymous paths are long enough, then the protocols provide provable security for some adversary models. However, it was assumed that all users choose intermediate servers uniformly at random from the same set of servers.
We show that if a single user chooses only from a constrained subset of possible intermediate servers, anonymity level may dramatically decrease. A thumb rule is that if Alice is aware of much less than 50% of possible intermediate servers, then the anonymity set for her message becomes surprisingly small with high probability. Moreover, for each location in the anonymity set an adversary may compute probability that it gets a message of Alice. Since there are big differences in these probabilities, in most cases the true destination of the message from Alice is in a small group of locations with the highest probabilities.
Our results contradict some beliefs that the protocols mentioned guarantee anonymity provided that the set of possible intermediate servers for each user is large.
KeywordsAdditional Server Adversary Model Total Variation Distance Anonymous Communication True Destination
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- 1.Agrawal, D., Kesdogan, D., Penz, S.: Probabilistic Treatment of MIXes to Hamper Traffic Analysis. In: Proceedings of the IEEE Symposium on Security and Privacy (2003)Google Scholar
- 4.Chaum, D.: Secret-Ballot Receipts and Transparent Integrity. Better and less-costly electronic voting and polling places, Available at http://theory.lcs.mit.edu/~rivest/voting/papers/Chaum-SecretBallotReceiptsTrueVoterVerifiableElections.pdf
- 5.Czumaj, A., Kanarek, P., Kutyłowski, M., Loryś, K.: Distributed Stochastic Processes for Generating Random Permutations. In: ACM-SIAM Symposium on Discrete Algorithms SODA 99, 271–280 (1999)Google Scholar
- 6.Danezis, G.: Designing and Attacking Anonymous Communication Systems. CAM-CL-TR-594, University of Cambridge, Computer Laboratory (2004)Google Scholar
- 9.Dingledine, R., Mathewson, N., Syverson, P.: Tor: the Second Generation Onion Router. USENIX Security (2004)Google Scholar
- 12.Goldschlag, D.M., Reed, M.G., Syverson, P.: Private Web Browsing. Journal of Computer Security, Special Issue on Web Security 5, 237–248 (1997)Google Scholar
- 13.Gomułkiewicz, M., Klonowski, M., Kutyłowski, M.: Provable Unlinkability Against Traffic Analysis Already After O(log(n)). In: Steps! Information Security Conference 2004. LNCS, vol. 3381, pp. 229–238. Springer, Heidelberg (2004)Google Scholar
- 14.Jakobsson, M., Juels, A.: Mix and Match: Secure Function Evaluation via Ciphertexts. In: Advances in Cryptology - Asiacrypt 2000. LNCS, vol. 1976, pp. 162–177 (2000)Google Scholar
- 19.Rackoff, C., Simon, D.R.: Cryptographic Defense Against Traffic Analysis. In: ACM Symposium on Theory of Computing(STOC), vol. 25, pp. 672–681 (1993)Google Scholar