[cryptography] One Time Pad Cryptanalysis

Greg Rose ggr at seer-grog.net
Wed Oct 2 15:23:00 EDT 2013


On Oct 2, 2013, at 10:43 , Peter Saint-Andre <stpeter at stpeter.im> wrote:

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> On 10/2/13 10:38 AM, danimoth wrote:
>> On 02/10/13 at 08:51am, Florian Weimer wrote:
>>> There is widespread belief that compressing before encrypting
>>> makes cryptanalysis harder, so compression is assumed to be
>>> beneficial.
>> 
>> 
>> Any academic references?
>> 
>> Without these, IMHO your sentence is false.
> 
> Since when are academic references needed to assert that something is
> widely believed? ;-)

The redundancy of the plaintext contributes to the unicity distance of the cipher. Compression reduces redundancy. Therefore, the unicity distance for compressed plaintext (that is, the amount of cipher text required before a unique key can be determined by brute force) must increase. Now, this is only one kind of attack, but it is an attack that is made more difficult by compression. Practically, I don't think this is much of an argument for compression, but it's more than just "a widespread belief"; there is theory behind it.

Greg.
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