From: SINCLAIR  DOUGLAS N <sinclai@ecf.toronto.edu>
Date: Thu, 12 May 94 07:24:33 PDT
To: klbarrus@owlnet.rice.edu (Karl Lui Barrus)
Subject: Re: Message Havens
In-Reply-To: <9405120451.AA27627@flammulated.owlnet.rice.edu>
Message-ID: <94May12.102413edt.13411@cannon.ecf.toronto.edu>
MIME-Version: 1.0
Content-Type: text/plain


Downloading the whole message base to scan for one's messages
will place a massive load on net.resources, and probably
a prohibitive load on most people's terminals.  This scheme
should avoid this nescessity:

Alice wishes to write a message anonymously to Bob.  They have
agreed in previous communications that their tag is the string "foo".
Alice writes her messages, and encrypts it with Bob's public key.
She then prepends the tag.  It looks like this:

Tag: foo
--- Begin Pgp Message ---
zxcvm,/asdfjk;qup
....
iuerpw,d,fy
--- End Pgp Message ---


Next, she encrypts this with the gopherhole's public key.  The
resulting message is posted to the gopherhole, where it is decrypted
and made available for all to download.

Now, Bob enters the gopherhole and instructs it to download all
messages with the tag of "foo".  To thwart trafic volume analysis,
he also downloads messages with tags "bar", "baz" and "quux", which
he then discards.

Problems:
The gopherhole must be trusted not to divulge which posts
came from who, and it's key must not be compromized.

A tap on Bob's line shows that he /may/ have a connection with
the "foo" tag.  However, the only person that knows anything
about that tag is Alice.  Thus, the other party in the conversation
must colaborate in an attack, probably ruining her anonymity.

Comments?