In message <[EMAIL PROTECTED]>, Greg Broiles writes:
>
> What scares me is the possibility that there won't even be an argument
> about whether or not a particular clump of ciphertext decodes to a
> particular bit of plaintext because I don't think it'll be possible to
> cross-examine prosecution witnesses about the way that they came into
> possession of what's purported to be plaintext. They won't need to say
> how they came into possession of the plaintext, because that would
> reveal their methods - if you know what ciphertext they used (especially
> if you're seeing it as an email message (perhaps with Received lines
> intact), or as the output of tcpdump) you probably know how it was
> intercepted, and that's something they want to keep secret.
In fact, there's precedent here. Elizabeth Friedman cryptanalyzed the codes
used by rum-runners during Prohibition. The cryptanalysis was challenged
(though not very well...) by the defense. The judge allowed that line of
questioning. (Kahn, "The Codebreakers", Chapter 22.)
>
> The scenario I'm concerned about is a simple swearing/credibility
> contest - the prosecution witness asserts that the defendant was the
> author of a particular (plaintext) communication which is either a
> crime, or admits to committing a crime. The defense can now choose
> between offering no response, or having the defendant deny authoring the
> communication (under oath, waiving their right against
> self-incrimination, including related to collateral matters). The
> defense won't have a meaningful opporunity to question the technical
> correctness nor the constitutional/legal appropriateness of the access
> to the text, because it's not possible to meaningfully explore those
> issues without revealing the government's methods.
Of course, it's by no means obvious that a judge will permit that provision to
stand. A more likely outcome is similar to the anti-"greymail" law, where the
judge gets to examine the evidence privately. If it's useless to the defense,
it's excluded without disclosure. If, on the other hand, it's germaine, the
prosecution gets its choice: drop the charges, or reveal the secret
information.
--Steve Bellovin
