Hi everyone,

I recently ran into a paper on convergent encryption, which is a way of 
encrypting file blocks by their hashes. The hashes (keys) are stored 
with the blocks, encrypted with the public key of any authorized 
readers. This allows a server to pool identical files, as they end up 
having identical encrypted blocks. This would allow BackupPC to still 
work as it does now. Naturally, file size, location, quantity, etc are 
visible but the contents wouldn't be.

I'm not sure if this has been suggested before, but a brief peruse of 
the archives didn't turn anything up. It seems like the arguments 
against encryption in the past found the pooling issue insurmountable.

I appended bibtex for the paper below.

Cody



@INPROCEEDINGS{Douceur02Reclaimingspacefrom,
   author = {J.~R. Douceur and A. Adya and W.~J. Bolosky and P. Simon 
and M. Theimer},
   title = {Reclaiming space from duplicate files in a serverless 
distributed
        file system},
   booktitle = {ICDCS '02: Proc. 22nd International Conference on 
Distributed Computing
        Systems},
   year = {2002},
   pages = {617--624},
   month = {2--5 July },
   abstract = {The Farsite distributed file system provides availability 
by replicating
        each file onto multiple desktop computers. Since this replication
        consumes significant storage space, it is important to reclaim used
        space where possible. Measurement of over 500 desktop file systems
        shows that nearly half of all consumed space is occupied by duplicate
        files. We present a mechanism to reclaim space from this incidental
        duplication to make it available for controlled file replication.
        Our mechanism includes: (1) convergent encryption, which enables
        duplicate files to be coalesced into the space of a single file,
        even if the files are encrypted with different users' keys; and (2)
        SALAD, a Self-Arranging Lossy Associative Database for aggregating
        file content and location information in a decentralized, scalable,
        fault-tolerant manner. Large-scale simulation experiments show that
        the duplicate-file coalescing system is scalable, highly effective,
        and fault-tolerant.},
   doi = {10.1109/ICDCS.2002.1022312},
   url = {http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1022312}
}

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