[tahoe-dev] Recombinant Hashes

Chris Dew cmsdew at googlemail.com
Thu Feb 11 18:47:26 UTC 2010

Reading http://www.google.co.uk/url?sa=t&source=web&ct=res&cd=4&ved=0CB0QFjAD&url=http%3A%2F%2Fwww.dss.uwaterloo.ca%2Fpresentations_files%2FDSS_Shokrollahi.pdf&ei=OU50S_yuBMeOjAfU4MmWCg&usg=AFQjCNHiXdzO9TgsiBAuunbLVNLpADY0mA&sig2=LA8uynb1ePs27YmNSyErdQ
it looks like my algorithm has the advantage that it 100% guarantees
successful reconstruction given parts whose length total one byte more
than the original data.  It may have performance disadvantages.

I'll comment and port the algorithm to C and put it up on the web when
I next get an hour or two.



On 11 February 2010 18:22, Chris Dew <cmsdew at googlemail.com> wrote:
> Yes, my algorithm seems to have the properties of a fountain code.
> Thanks for the link - I hadn't heard of fountain codes before.  It
> seems that I haven't discovered something new :-(
> All the best,
> Chris.
> On 11 February 2010 18:10, Brian Warner <warner at lothar.com> wrote:
>> 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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> --
> http://www.finalcog.com/



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