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1997-08-13 - Re: Encrypting same data with many keys…

Header Data

From: amp@pobox.com
To: ghio@temp0107.myriad.ml.org>
Message Hash: 83b647f98390ea6da4a819c057d20c190a00ef78c97ac48104c1917a795d8c3f
Message ID: <Chameleon.871421963.amp@ampugh.mcit.com>
Reply To: <Pine.SUN.3.96.970812111223.26326D-100000@beast.brainlink.com>
UTC Datetime: 1997-08-13 00:29:39 UTC
Raw Date: Wed, 13 Aug 1997 08:29:39 +0800

Raw message

From: amp@pobox.com
Date: Wed, 13 Aug 1997 08:29:39 +0800
To: ghio@temp0107.myriad.ml.org>
Subject: Re: Encrypting same data with many keys...
In-Reply-To: <Pine.SUN.3.96.970812111223.26326D-100000@beast.brainlink.com>
Message-ID: <Chameleon.871421963.amp@ampugh.mcit.com>
MIME-Version: 1.0
Content-Type: text/plain



> > 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.



------------------------
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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