SCHEME for FULL-SPEC RETURN PATH

17 Dec 2003

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 This is a portion of mail that I sent to bill stewart.  Since bill seems to
 busy to send a critique, could someone else comply, please?

 Jon Boone | PSC Networking | boone@psc.edu | (412) 268-6959 | PGP Key # B75699
 PGP Public Key fingerprint =  23 59 EC 91 47 A6 E3 92  9E A8 96 6A D9 27 C9 6C

- ------- Forwarded Message

Date: Thu, 03 Feb 94 13:45:31 -0500
From: "Jon 'Iain' Boone" <boone@psc.edu>

  How secure do you think this is?

  Three remailers:

  anon1+@a.edu
  anon2+@b.com
  anon3+@c.org

  Originator: boone@psc.edu (really igi.psc.edu, as Message-ID: shows)
  Receiver: wcs@anchor.ho.att.com

  ()Ka == contents inside () are encrypted with Public Key of A

  mail addressed to random+*@foo.edu == mail to user random@foo.edu,
					random's mail processor will
					deal with the +*

  The sender must encrypt his/her own address with the public key of the
  first remailer and put it in the X-A-R-P: field.

  Upon reciept of a message with X-A-S-P: set to non-empty, the re-mailer
  will strip off its portion of the address and decrypt the rest with its
  private key.

  It will add itself to the X-A-R-P: and encrypt it in the public key of
  the next remailer on the X-A-S-P:

  If there is nothing in the X-A-S-P: (after having removed its own address),
  then it needs to be sent to the To: address, so we set the From: address to 
  be the contents of the X-A-R-P: with its own address pre- & post- pended.  
  That way, the reciepient need not change his/her mail agent to respond via 
  the X-A-R-P: (or even need to include the X-A-S-P: in the outgoing response).

  If the message doesn't have an X-A-S-P:, the remailer checks the "To:"
  for the contents of what would have been the X-A-S-P: with its own address
  pre- & post- pended.  By stripping off its own address and de-crypting the
  resultant, it has the next address to send it to. 

  Barring wire-tapping, your privacy is susceptible in the logs (syslog, etc.)
  of the first remailer (a.edu in my example) or if all the RSA-keys for
  a.edu, b.com and c.org are broken.  To dampen wire-tapping, you could encrypt
  the contents of the message with padding, making traffic analysis more
  difficult.

  Comments?

  IGI.PSC.EDU:

  To: wcs@anchor.ho.att.com
  X-A-S-P: anon1+"(anon2+"(anon3+@c.org)Kb"@b.com)Ka"@a.edu
  X-A-R-P: (boone@psc.edu)Ka
  From: boone@psc.edu
  Message-Id: <348723472.AA34890235@igi.psc.edu>

  A.EDU:

  To: wcs@anchor.ho.att.com
  X-A-S-P: anon2+"(anon3+@c.org)Kb"@b.com
  X-A-R-P: (anon1+"(boone@psc.edu)Ka"@a.edu)Kb
  From: anon1+@a.edu
  Message-Id: <2349458.AA23575@a.edu>

  B.COM:

  To: wcs@anchor.ho.att.com
  X-A-S-P: anon3+@c.org
  X-A-R-P: (anon2+"(anon1+"(boone@psc.edu)Ka"@a.edu)Kb"@b.com)Kc
  From: anon2+@b.edu
  Message-Id: <8980234.AA23489203@b.com>

  C.ORG:

  To: wcs@anchor.ho.att.com
  X-A-R-P: anon3+"(anon2+"(anon1+"(boone@psc.edu)Ka"@a.edu)Kb"@b.com)Kc"@c.org
  From: anon3+"(anon2+"(anon1+"(boone@psc.edu)Ka"@a.edu)Kb"@b.com)Kc"@c.org
  Message-Id: <2343.AA123@c.org>

  ANCHOR.HO.ATT.COM: (Reply) 

  To: anon3+"(anon2+"(anon1+"(boone@psc.edu)Ka"@a.edu)Kb"@b.com)Kc"@c.org
  From: wcs@anchor.ho.att.com
  Message-Id: <99234.AA23492383@anchor.ho.att.com>

  C.ORG:

  To: anon2+"(anon1+"(boone@psc.edu)Ka"@a.edu)Kb"@b.com
  From: wcs@anchor.ho.att.com
  Message-Id: <2342349324.AA2343242@c.org>

  B.COM:

  To: anon1+"(boone@psc.edu)Ka"@a.edu
  From: wcs@anchor.ho.att.com
  Message-Id: <98234234.AA123213@b.com>

  A.EDU:

  To: boone@psc.edu
  From: wcs@anchor.ho.att.com
  Message-Id: <7732432.AA52342@a.edu>

  Of course, some work would be necessary to accomodate double-blind
  conversations.