Multi-plaintext decryption (Was: Re: "Concryption" Prior Art)

[futplex@pseudonym.com (Futplex)]

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Allen writes:
> 	A section of data is placed at the beginning of the encrypted material.
> When it is decrypted or encrypted (depending on how one wants to work things)
> with a given passphrase, it turns out a series of bits, reiterated as needed.
> Each x bits is used to say how far along in the encrypted material the next
> piece of information making up one encrypted message (using the same
> passphrase) is. If you put in a different passphrase, you get a different
> series of bits, and thus use a different set of information for the encrypted
> material. 

This general concept crops up periodically here. As near as I can make out,
the object of the exercise is to be able to demonstrate an innocuous 
decryption of a piece of ciphertext which also has alternate corresponding 
plaintext messages.  Any scheme for this seems to depend upon the secrecy of
the algorithm, among other factors. If an adversary has some inkling that a
piece of ciphertext may represent multiple plaintexts, then she is unlikely to
be fooled by protestations to the contrary. So IMHO it is rather pointless to
debate possible designs for such a scheme. Those who remain interested would
do well to read the various previous discussions about this in the archives.

Futplex <futplex@pseudonym.com>			"Of course I'm celebrating! 
		Dallas only wins the Super Bowl once a year, you know...."

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