From: Scott McGuire <svmcguir@syr.edu>
Date: Thu, 10 Oct 1996 16:24:15 -0700 (PDT)
To: cypherpunks@toad.com
Subject: Re: "Forward Privacy" for ISPs and Customers
In-Reply-To: <325c26935621002@noc.tc.umn.edu>
Message-ID: <ML-2.2.844989814.7457.scott@homebox.>
MIME-Version: 1.0
Content-Type: text/plain


Kevin L Prigge said
> Timothy C. May said:
> 

... stuff deleted ...

> > Something ISPs could do--and may do if there is sufficient customer
> > pressure--is to adopt a policy of "forward secrecy" (to slightly abuse
> > this technical term). That is, to have an explicit policy--implemented
> > in the software--of _really_ deleting the back messages once a customer
> > downloads them to his site. This means that _backups_ must be done in a
> > careful manner, such that even the backup tapes or disks are affected by a
> > removal. 
> 
> Interesting thought, but it fails when it gets to my scale. It would
> be trivial to exclude a file or set of files from normal backup, but
> it would be problematic to exclude files from filesystem dumps, etc.
> The scale I deal with (40,000 users, 12gb of /home directory files and
> about the same in the mail spool) would make it almost impossible to
> provide this service with accuracy to my users.
> 
How hard would this be? (and would it work?)

Use an encrypted file system, something like Matt Blazes CFS which allows each
user to set up his own encrypted directories.  The encryption is file by file
so that backups can be made by the system, but the backups are still encrypted.

Unlike CFS, this system would allow public key cryptography.  The system could
write to a directory using the public key, but only the user could read from
the directory.  As usual, to speed things up, the PK cryptography would just be
used to encrypt/decrypt conventional keys which would be used for the
encryption/decryption of the data.  With this in place, when email comes in, it
could be stored in the recipient's directory of the hard drive.  I guess I'm
assuming that the user has a shell account.

> 
> -- 
> Kevin L. Prigge                     | Some mornings, it's just not worth
> Systems Software Programmer         | chewing through the leather straps.
> Internet Enterprise - OIT           | - Emo Phillips
> University of Minnesota             |
> 
> 

--------------------
Scott V. McGuire <svmcguir@syr.edu>
PGP key available at http://web.syr.edu/~svmcguir
Key fingerprint = 86 B1 10 3F 4E 48 75 0E  96 9B 1E 52 8B B1 26 05