Saving Opportunistic Encryption

[Tarapia Tapioco]

We've recently seen FreeS/WAN die, not least due to the apparent
practical failure of Opportunistic Encryption. The largest blocking
point for deployment of OE always seemed to be the requirement for
publishing one's key in the reverse DNS space. While most tech-savvy
people are able to get access to forward domain space, reverse DNS space
is still more heavily centralized and thus inaccessible to the general
public.

So, the apparent solution for me seems to be the approach that the SPAM
blacklists used - publish information in a subspace of the forward DNS
space instead of using the authoritative in-addr.arpa area.

A possible implementation looks like this:

* Keys are kept in TEXT record like with old-style OE, as
  a.b.c.d.opportunistic.net.

  The format of the text record contains
  * IKE authentication RSA key
  * optional "secure" owner identity, as in x.509 or PGP sig.
  * server signature.

On the client side:

* Keys are published via a TCP client. This ensures there's a
  minimal level of authentication that the submitter of a key is
  also in control of the IP address. Additionally, when an overwrite
  is attempted, we could attempt to obtain an ICMP echo response over
  the old SA and only accept the update when the old SA is dead.

* J. Random libpcap application listens for traffic to different IP
  addresses and checks said DNS repository, manipulates security policy
  accordingly.

This is just a dirty hack since it necessarily misses packets when the
other node is first contacted, but it seems to be the easiest hack-me
route, and it requires little to no platform integration, just
 * a libpcap implemenation
 * a command line interface to IPSEC security policies

Check at least for Linux and Windows, probably *BSD too.

* Linux/KAME's IKE daemon racoon is patched to attempt retrieval of an
  RSA key from said DNS repository and generate appropriate security
  policies.

Cleaner solution, but more work probably.

Obvious weaknesses: As the SPAM blacklists showed impressively, running
an unpopular service on the net these days will get you DDoS'ed out of
existence. Distributing the keys over the whole DNS space like FreeS/WAN
OE did is the cleanest solution here, but I guess a cypherpunkly
approach would also be "good enough" to get this thing started: Just use
a configurable list of domains instead of just opportunistic.net, each
with a different key, and publish these lists like those for remailers
are currently published.

Thoughts?

(On a side note, minder.net has dropped a lot of my recent posts via remailers.
Is there a better node for this?)