Protection mail at rest

Victor Duchovni Victor.Duchovni at morganstanley.com
Sun Jun 1 00:07:48 EDT 2008


On Fri, May 30, 2008 at 03:04:34PM -0400, Leichter, Jerry wrote:

> 
> 	1.  Client only.  The client, whenever it sees a new message,
> 		(a) downloads it; (b) encrypts it using a secret key;
> 		(c) stores the encrypted version back on the server;
> 		(d) deletes the unencrypted version.  The client can
> 		put the encrypted messages in a different folder, or
> 		it can mark them with a header line.
> 
> 	2.  Server-assisted.  The client gives the server its public
> 		key.  When a message arrives at the server, the
> 		server (a) generates a "session" key; (b) encrypts
> 		the message using the session key; (c) encrypts
> 		the session key with the client's public key;
> 		(d) adds a header containing the encrypted session
> 		key to the encrypted message; (e) stores the
> 		encrypted message.  The necessary work for
> 		the client is obvious.

	3. The server that stores your mail is not the first one to
	receive it. It is just the storage layer. A previous non-storing
	server, encrypts the mail and *then* forwards it to the store.

> In each case, one would probably chose some headers to encrypt
> separately - e.g., the subject - so that one could more easily pull
> them out without decrypting the whole message.

    S/MIME does not encrypt any headers. It only encrypts the
    payload. Some S/MIME applications don't leave any useful
    headers in the outer message, others leave the sender and
    subject in the clear.

> Does anyone know of existing work in this area?

Take PGP Universal gateway and turn-it inside-out. Clear mail on the
Internal encrypted mail on the intranet between the gateway and the
mail store.

Take a vanity domain, run an encryption gateway, forward everything to to
an ESP. The ESP's search engine will not do you much good with encrypted
mail, so indexing is up to your IMAP client, if it can cache/index
decrypted content.

Not much demand for this yet, so I don't expect mature offerings any
time soon. We'd have to build a boutique service for cipher-punks.

-- 

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