Re: Anybody know details about Schneier's "flaw"?

Carl Ellison <> Sat, 17 August 2002 12:56 UTC

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Date: Sat, 17 Aug 2002 05:42:29 -0700
From: Carl Ellison <>
Subject: Re: Anybody know details about Schneier's "flaw"?
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At 03:13 AM 8/16/2002 +0100, Adam Back wrote:

>Also the attack for those who haven't read the paper is really
>low-tech.  They're just observing that if you can ask someone to
>decrypt a message you can use that to decrypt related messages.  So
>you intentionally garble a message, and hope the user sends you the
>garbled plaintext back to you to ask what went wrong.  The rest
>falls out of the fact that if you garble a few bits of a ciphertext
>most of the plaintext will still be intact.

Y'know, there's an even simpler attack with the same premise.  You
intercept an encrypted e-mail from Alice to Bob.  You take the mail
body out of the message and send that body to Bob under your e-mail
address (or under some address you control that Bob might mistake for
Alice's, which would be even better).  Bob decrypts the message and
replies to it, including the original message body by default.

The mistake here, on Bob's part, is to reply to a message without
paying attention to the e-mail address being used -- rather than
replying to a message with quoted garbage rather than just saying
"that was garbage -- send again".

 - Carl

Version: PGP 6.5.8


|Carl M. Ellison |
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