Encrypted MLs (Was: api for gpg?)

[Werner Koch]

Hi Anand,

Anand Kumria <wildfire at progsoc.uts.edu.au> writes:

> When you communicate there are four different modes you can communicate
> in.  Single Sender, Single Receiver (SS); Single Sender, Multiple
> Receivers (SM); Multiple Senders, Single Receiver (MS) and Multiple
> Senders, Multiple Receivers (MM). 

Examples:
SS = private email
SM = anouncement MLs
MS = bug reports
MM = MLs

> I can see some immediate uses for Single Sender/Mltiple Receiver crypto;
> one would be in the Debian group. new-maintainer at debian.org actually goes
> to a number of people, in order to send a crypted message to them I need
> to know who those people are, what their current correct public keys are

We came up with a simple solution for a multiple receivers system:

 1) a file with the keyids (or the complete email address) of all
    subscribers is created and each id is prefixed with "-r " 
 2) gpg is run with "--options file-with-keyids-from-step-1" and
    creates a valid message to the n receivers. This file is 
    stored on disk
 3) a tool is used to cut off one receivers public-key encrypted
    session-key and the encrypted messaage id from the file created
    in step 2 and this is passed to sendmail.
 4) continue with step 3 but use the next user-id.
    
This is quite easy but we have to do a lot of calculations.

> I can see some initial problems: key generation, secret sharing, secret
> recombination/splitting, manipulating group membership, etc. No doubt

I guess that a secret sharing scheme could heavily increase the
performance but key distribution would be quite complex.  Perhaps 
we should think about a n-party DH scheme which has some security
advantages.


Werner