[tahoe-dev] proposal: add padding

Tony Arcieri tony.arcieri at gmail.com
Fri Jul 12 15:57:03 UTC 2013


On Fri, Jul 12, 2013 at 2:37 AM, Iraklis . <leontiad at gmail.com> wrote:

>  You are missing the following:
> Files are encrypted for deduplication. That implies a way to derive a key
> from the content of the files. That is if two files are similar they will
> have similar ciphertexts
>

No, because they are encrypted under a key derived by a hash function, and
one property of a secure hash function is that similar content produces
completely different hashes, even if you just change one bit.

Using this content hash to seed a PRNG (and derive encryption keys for the
content) will produce completely different pseudorandom padding, even for
similar files.

-- 
Tony Arcieri
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