Re: Making Remailers Widespread [REMAILERS]

[Bill Stewart <stewarts@ix.netcom.com>]

At 09:37 AM 9/29/96 EDT, you wrote:
>How about: maintain a list of trusted blocking-list sites (comparable to the
>list of remailers used for chaining) and when it comes the time to update the
>local copy of the blocking list, ask a random one on the list; if it's down,
>ask another random one on the list. There may even be more than one list. :-)

Getting more complex, but it might be workable.


>> sender-blocking list 
...
>With most ISP's it's trivial to forge one's From: header in SMTP.
>Switching to another dime-a-dozen throwaway account is also trivial.
>Just admit that you can't block senders, and don't pretend that you
>can - false pretenses destroy one's credibility.

You obviously can't source-block a determined spammer, but you can
slow down some spam attacks, especially if they're one individual 
using his/her regular account.  It's no panacaea, but it helps.
Also, if you source-block based on patterns anywhere in the header,
you can catch less capable email forgers.


>I think I see a way to accomplish this without too much trouble.
>When an e-mail is directed at u@c4.c3.c2...c1, the code that checks
>for blocking will search for the following records in the blocking list:
>u@c4.c3.c2...c1     (exact match)
>*@c4.c3.c2...c1     (replace user by *)
>u@*.c3.c2...c1      (replace leftmost .-separated piece of domain by *)
>*@*.c3.c2...c1      (both)
>and repeat until there are only 2 components left in the domain name.

That'd work.  It's clunky, but there's no avoiding clunkiness
for this sort of thing, and it does preserve privacy.

>Now, the question is, who would be allowed to add records containing
>'*' to the blocking list using the cookie protocol? I suggest that it be
>one of the contacts listed in Internic's database.

postmaster@domain is (ostensibly) guaranteed to exist.
The Internic database is an interesting alternative, but for this
I suspect postmaster is good enough.  There's also the problem
that for many domains, where smallcompany.com is virtual on an ISP,
the Internic database will generally list someone at the ISP,
who probably has no interest in the issue, rather than someone
responsible for making decisions about smallcompany.com

>Thus a blocking record for cypherpunks@toad.com could be added by
>anyone listed in toad.com's Internic entry.  There's no need for any
>Remailer Cabal [tinc] to maintain blocking lists.

For destination blocking, I agree that users should be able to 
block their own stuff as automagically as possible.
For source blocking, most of the need is for spams and abusers
that have been tracked down (or identify themselves in their postings),
and that takes human thought.  In particular, spammers are unlikely
to block themselves from the remailers (:-), but forgers may try to block
legitimate users.

>One other suggestion: instead of storing one bit of information (the
>address is on the list or not), why not have several flag bits.
>E.g., the blocking list could contain records similar to:
>hash - e.g. 160-bit SHA
>flags - e.g. reserve 32 bits

Interesting.  I suspect the state of the art would be to collect
the bits with a disclaimer that there isn't any code to interpret them :-),
but it does let you build a blocking database that's usable as capabilities
grow.
Any suggestions for flags besides block/allow one-way, block/allow two-way,
and max-size?  I'm thinking of doing a remailer that instead of sending
you a message, it sends you a retrieval cookie and lets you send it back
to collect the message; blocking that would be another flag.

The other kind of blocking that needs adding is blocking by
words in message bodies - the spammer that caused me to shut down
my remailer and not bring it back up was posting hate messages
with somebody else's name and email signed at the bottom.  
It only took one or two to generate a flood of flames to the victim,
and my current remailer couldn't block any followups.
Also, since the spammer wasn't generating the flames himself,
his spam slipped under the remailer's spam counter, just as
hipcrime's did.  This sort of blocking also lets you block
things like the hipcrime spam and MAKE MONEY FAST.
But it's a much more sensitive problem - anybody who can add things
to the body-checking list can start doing real censorship,
and it's probably best to leave that to individual operators to block,
or at least to turn on by hand rather than default.

#			Thanks;  Bill
# Bill Stewart, +1-415-442-2215 stewarts@ix.netcom.com
# <A HREF="http://idiom.com/~wcs"> 	
# You can get PGP software outside the US at ftp.ox.ac.uk/pub/crypto