[tahoe-dev] proposal: add padding

[Iraklis .]

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
and subsequently as proposed equivalent pads since the pad would be the 
result of a PRNG seeded under the same deterministic key.
So in our case we are discussing not for 11 & 12 but for 11 & 11 or 12 & 12.

Regards,

Iraklis
On 07/12/2013 11:27 AM, Olaf TNSB wrote:
>
> Am I missing something simple here?  You pad pre-encryption and unless 
> the encryption algorithm is completely flawed then slightly different 
> input files will give completely different output.
>
> In a similar (but entirely unrelated way!) look at the 
> MD5/SHA256/your-fav-hash-function of the numbers 11 & 12. Do you see 
> any similarities in the hash?
>
> Olaf
>
> On 12/07/2013 5:58 PM, "Iraklis ." <leontiad at gmail.com 
> <mailto:leontiad at gmail.com>> wrote:
>
>     But still someone can identify the common pattern at the end of
>     two or more similar files so the pad can be detected and deleted,
>     thus length is not hidden.
>     On 07/11/2013 09:01 PM, Tony Arcieri wrote:
>>     On Wed, Jul 10, 2013 at 7:31 AM, Ed Kapitein <ed at kapitein.org
>>     <mailto:ed at kapitein.org>> wrote:
>>
>>         Hi Zooko,
>>
>>         Be careful with zero padding, it might leave the data open for a
>>         watermarking attack.
>>
>>
>>     How about padding with the output of a PRNG seeded with the
>>     content hash? That way it'd still be deterministic
>>
>>     -- 
>>     Tony Arcieri
>>
>>
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