[tor-dev] Email-based rendezvous for flash proxies

David Fifield david at bamsoftware.com
Tue Sep 25 05:42:23 UTC 2012

I have made a design and written some code for an email-based
registration system for flash proxy clients. Registration is the process
by which a censored client sends its IP address to request service from
an external proxy.

In summary, a censored client sends its address in encrypted email over
SMTP over TLS to a distinguished email address. A program running on the
flash proxy facilitator makes an IMAP connection over TLS, polls for
messages, then decrypts them and registers the addresses withing. The
email messages are sent by a registration helper program, not the
client's own email account, and they appear to come from a dummy
address. More information is in the ticket:


I would appreciate a second look at the design, especially the use of
crypto. The ticket's comment number 5 calls out some particular

This is our first registration system with a claim to being hard to
block. This is step 1 that goes through the firewall in the diagram at
http://crypto.stanford.edu/flashproxy/#how-it-works. The censor sees a
TLS session with a Gmail MX server, followed later by an incoming
connection from a flash proxy at a previously unseen IP address. What
makes this different than other circumvention ideas is that nothing is
sent directly to any published or unpublished Tor relay.

David Fifield

More information about the tor-dev mailing list