caveat lector 2012-09-25 -- "The Science Fair episode" in attendance: Zooko (scribe), CodesInChaos, amiller, David-Sarah, elb Topic: proof-of-storage/proof-of-retrievability CiC suggested a pass-through "Chess Grandmaster" style attack of storage server which doesn't hold the data but queries other servers to answer challenges. amiller suggested that perhaps not knowing the verify cap would prevent a storage server from doing that. CiC pointed out that if you are a malicious storage server who wants to defect, you won't do that when there are K other, non-malicious, storage servers online. You might as well wait until there are not enough non-malicious storage servers left, so that your defection can accomplish some real harm. CiC mentioned his standard merkle tree design, but didn't get much opportunity to say much about it. There was extensive discussion about the very notion of Proof-of-Storage and Proof-of-Retrievability, and how they could be applied to LAFS. I (Zooko) intend to write notes to tahoe-dev about it soon. David-Sarah had simulation results about the idea of Proof-of-Storage by adding erasure-coding redundancy to each share stored on an individual server. After CiC disconnected, amiller and davidsarah proposed standardizing a hash-dag instead of a hash-tree, with the tree being a special case of the dag. There was a bit about having a tweak to make hash collision attacks harder. Andrew Miller talked about the Bitcoin blockchain and a git repository are similar data structures. Zooko told Andrew Miller that digital signatures built out of secure hash functions normally use hash trees, but that one design, due to Bleichenbacher and Maurer, uses hash-dags instead. The full sub-graph of a LAFS filesystem which is reachable starting from an immutable dir constitutes a hash dag. Not so for mutable dirs. _______________________________________________ tahoe-dev mailing list tahoe-dev@tahoe-lafs.org https://tahoe-lafs.org/cgi-bin/mailman/listinfo/tahoe-dev ----- End forwarded message ----- -- Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org ______________________________________________________________ ICBM: 48.07100, 11.36820 http://www.ativel.com http://postbiota.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE