Improvement of remailer security

Matthew J Ghio mg5n+ at
Thu Mar 10 22:02:24 PST 1994

boldt at (Axel Boldt):

> Even the current pgp encryption scheme offered by some remailers
> doesn't help much, once the incoming and outgoing messages are
> known: just take the outgoing message from the remailer, encrypt
> it with the remailer's public key, compare this to the incoming
> messages and you know who sent this message (repeat if a chain
> of remailers was used).

Nope...  PGP encrypts the message with a random IDEA key, and then
encrypts the IDEA key with RSA.  You'd have to guess which IDEA key was
used, and encrypt that with RSA.  The SS couldn't guess 2^128 possible
IDEA keys in a hundred years, even with 10 cray supercomputers...  (of
course, they might be able to do it a hundred years from now... but by
then nobody would care about some stupid 20th century email message.)

Karl Barrus's latent-num and truncate-line features on his former
tree-remailer handled all of the traffic-analysis problems rather
nicely, however...

> Here's a proposal which could close this hole: remailers should
> allow for a new header 'Encrypt-with:' which takes as argument
> a public pgp key. This is used just like the 'Request-Remailing-To:'
> header, i.e. using the '::' construct in the body of the pgp encrypted
> mail. ('Encrypt-with:' offers no additional security if no pgp
> encryption is used in the first place.) The semantics is that the
> remailer, just before passing the message along (and after having
> decrypted it, of course) encrypts the message using this public key
> and adds an 'Encrypted: pgp' header to it.

JPP's remailer does this, except it only posts to alt.test.  Maybe you
could convince him to allow it to also forward to remailers when a
remailer public key is specified... :)

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