[rc5] key security question

Benedikt Eric Heinen beh at icemark.ch
Thu Jun 5 20:18:51 EDT 1997

I don't know about the specific details of the RC5 or other encryption
methods (neither do I have the mathematical knowledge to understand them),
but I am curious - what happens when I encrypt some plaintext using 56bit
RC5 and then encrypt the result with another RC5 56bit key.

How secure will the resulting file be? How do those keys work? 

  - Is there still a single 56bit key that can decrypt the file (i.e.
    the second encryption doesn't give any additional security)?

  - Do the bits just add up (i.e. the resulting ciphertext will be 
    like it was encrypted using a single 112 byte key)?

  - Do the keys multiply (i.e. the result would be like it was encrypted
    using a 56^2 bit key)?

  - Will the keys power each other (56^56 bit protection)?

I guess, it's either the first or third - I am not sure which one applies.
But - I'd be curious to know...



          Hiroshima '45           Chernobyl '86           Windows '95

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