[892] in cryptography@c2.net mail archive
A Possible Application for Proxy Crypto
daemon@ATHENA.MIT.EDU (Antonomasia)
Thu May 22 20:06:49 1997
Date: Thu, 22 May 1997 22:12:11 +0100
From: Antonomasia <ant@notatla.demon.co.uk>
To: mab@research.att.com, cryptography@c2.net
Matt Blaze <mab@research.att.com>
> I've put a draft of a new paper in my ftp directory. Comments and
> discussion welcome. In particular, I'm curious if anyone can find
> any real practical application for symmetric proxy functions.
>
> ftp://ftp.research.att.com/dist/mab/proxy.ps
I can imagine a use in remailer networks.
Currently a 'newnym' has one or more reply blocks stored on the
nymserver to send through a chain of type-1 remailers to a final
address where the nym owner can find his incoming mail.
These reply blocks contain text like
::
Anon-To: you@your.email.address
Latent-Time: +0:00
Encrypt-Key: passphrase_a
for each hop in the chain. So email finally arrives at the
nym owner encrypted several times. This means either a lot
of typing or some form of stored passphrase, neither very
desirable.
If the hop-by-hop encryption were public, rather than single-key,
a proxy scheme could allow remailers to apply proxy public encryption
keys to the text below the '**' marker.
::
Anon-To: you@your.email.address
Latent-Time: +0:00
Proxy-Key: decc5e762d84503ae50bd69a....longer....d893a6eb
This would keep the message encrypted by only one layer beyond
the nym's public key (if used). But no remailer would have access
to the plaintext. The ciphertext would change between one hop and
the next [1] hindering traffic analysis.
Suitably-chosen sets of reply blocks could make all incoming email
have the same final key, even if they followed different histories
in transit.
The fact that these suit symmetric proxy transformations is clear
from the fact that the nym owner is handling his own mail to
be decrypted by himself later. Indeed the current behaviour is
to use single-key encryption.
Comments on this ?
[1] - not fully true for the ElGamal formats seen so far
with ciphertext in two parts
keywords: proxy url remailers
--
###############################################################
# Antonomasia ant@notatla.demon.co.uk #
# (mail arcbot@notatla.demon.co.uk for cryptography archive) #
###############################################################
