> Hi, > > we are currently looking into different methods for censorship-resistant > publication in distributed systems using different replication techniques. > > I have a question regarding the anonymity of downloaded a file that is > split in a reasonable large number of blocks. Are the requests for all > blocks forwarded independently using FoF routing (or the hill-climbing > algorithm if FoF is disabled). > > If so, doesn't that enable the following attack: Assume an adversary > wants to find out if one of her peers is downloading the file. She can > obtain the manifest file and thus the CHK keys of all blocks. Someone > downloading the file will request all blocks, forwarding the requests to > different peers. These will forward the request to their peers. So > likely their peers will receive more block requests than non-peers. So, > if the adversary wants to find out if she is connected to the requester, > shouldn't receiving a high number of requests for the different blocks > of the same file be a really good indicator that this peer is the actual > requester and not only forwarding? The math is a bit more complicated, > as the the number of files per peer will not be uniform. Nodes have few > peers at a large distance and those have a higher chance of being the > closest peer to a CHK block (or have the closest peer to a key if FoF > routing is enabled). Nevertheless, I think this is clearly a serious > problem, if I understand what is happening correctly. > > Wouldn't it be better to add the possibility of forwarding all block > requests along the same link initially? It could be tied to the > probabilistic HTL decrease: Initiator/forwarder with HTL=18 of a request > uses random peer. If HTLDecrement==false is set for that connection, all > block requests are forwarded to that peer (or rather one request > including the manifest file), otherwise all of them are routed > individually as it is now (if that is what is happening now). Now, the > adversary can use the above attack to tell which peer started routing > rather than random forwarding but that might not be the requester. > > Any thoughts on that? > > Thanks, > > Stef >
-- Stefanie Roos Postdoctoral Fellow CrySP, University of Waterloo https://cs.uwaterloo.ca/~sroos/
