[tahoe-dev] Recombinant Hashes

Brian Warner warner at lothar.com
Thu Feb 11 18:10:04 UTC 2010


Chris Dew wrote:
> Hi, I just read about this project on Reddit, and wondered whether you
> use an algorithm similar to that which I've developed.
> 
> It lets you make an unlimited amount of hashes from some data.  So
> long as the total length of the hashes you possess are greater than
> the length of the original data, you can recreate the original data -
> regardless of which combination of hashes you possess.

I think we're using a similar approach. I haven't heard the term "hash"
for the pieces, though.. I've only heard "share" or "block" or sometimes
"packet" for the pieces. (using "hash" seems likely to get confused with
a secure cryptographic hash, from which you'd never be able to get back
to the original data, of course).

We use Reed-Solomon erasure coding, which produces a limited number of
shares. There is a different sort of erasure codes called Fountain Codes
which can produce an effectively-unlimited number of shares
(http://en.wikipedia.org/wiki/Fountain_code) .. is your algorithm like
one of those?

cheers,
 -Brian




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