Re: Encrypting same data with many keys...

[amp@pobox.com]

> > What are the dangers of taking a small block of data - say upto 1K in
> > size, then producing many files, each being the same data encrypted by
> > other keys?
> ...
> > Assume we're using 128 bit Blowfish/Idea or better, and discarding
> > weak keys.
> 
> For a standard block cipher there should be no problem.  For a stream
> cipher, you would have the same type of problems as for OTP reuse, but
> it would still be secure as long as you never reused a key.  However...
> 
> > What if instead of using a private key cypher, we used a public key
> > cypher?  Would that make any difference in attack methods?
> 
> Yes.
> 
> Having identical plaintexts raised to the same power modulo different
> numbers makes the solution much easier.  If you have enough RSA
> encryptions of the same number to the same power, you can solve it
> outright by the remainder theorem.

So would that then be a possible weakness in encrypting to multiple 
recipients with PGP? Probably not, since the actual data is encrypted with 
idea.



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Name: amp
E-mail: amp@pobox.com
Date: 08/12/97
Time: 17:37:16
Visit me at http://www.pobox.com/~amp

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