[rc5] Some Deep questions

Ivo Janssen ivo at ricardis.tudelft.nl
Mon Aug 18 10:52:19 EDT 1997


On Sun, 17 Aug 1997, Ryan Dumperth wrote:

> >Specifically, how are the results checked?  What knows
> >when we've hit the right key?  Does the client, do the
> >servers?  And how do they know it?
> 
> http://www.rsa.com/rsalabs/97challenge/html/rules.html
> 
> RSA has made it clear what they did to the plaintext to come up with the
> ciphertext. The only thing we haven't been told is the secret key. It is my

OK, so RSA is nice to us. We know the exact beginning of the
plaintext. But what if real encrypters are not so nice, and do, as
said, a simple ASCII+1, or even another rc5. Double RC5. To brute
force crack that one, you have 2^112 possibilities. Even if we speed
up our computers with a factor 2^56, it would still take a year or
so.

BTW, there must exist a way to revert te encryption. One way
encryption is never one way, they just made it difficult to do the
other way around. My point is: it can never be harder to use
intelligent methods to break the code then just brute force.

So is there a smart method to break RC5??

Ivo

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