Re: how to tell if decryption was successfull?

2005-02-02 Thread Steven M. Bellovin
In message [EMAIL PROTECTED], Andreas writes:
[newbie here]

I was wondering how can one tell if some data was successfully 
decrypted. Isn't there an assumption going on about what the cleartext 
data should be? Text? Image? ZIP file? Ziped jpeg? Another cyphertext? 
rot-13?

There are a lot of ways to tell, but you generally have to have some 
idea what you're looking for.  For two examples of how to do it, see
http://www1.cs.columbia.edu/~smb/papers/probtxt.ps (or .pdf) and
http://www1.cs.columbia.edu/~smb/papers/recog.ps (or .pdf)

--Prof. Steven M. Bellovin, http://www.cs.columbia.edu/~smb



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Re: how to tell if decryption was successfull?

2005-02-02 Thread Matt Crawford
On Feb 1, 2005, at 13:29, Andreas wrote:
I was wondering how can one tell if some data was successfully 
decrypted. Isn't there an assumption going on about what the cleartext 
data should be? Text? Image? ZIP file? Ziped jpeg? Another cyphertext? 
rot-13?
Embedded checksums or hash codes added before encryption.  The types of 
those checks must not interact badly with the encryption.

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