Re: [Asrg] Please critique my anti-spam system

["Tripp Cox" <tripp at corp.earthlink.net>]

I've been thinking a bit more recently about schemes like this, and they 
generally revolve around the practice of giving the recipient some kind of 
unique namespace and permitting them to create as many names within that 
space as they wish.  This creates the potential, but not the necessity, for 
the recipient to use one-time or disposable email addresses.  The most 
common suggestion in this realm is to use context indicators in the local 
part of an otherwise static local part.  For example, I might subscribe to 
mailing lists as tripp+lista at corp.earthlink.net, 
tripp+listb at corp.earthlink.net, etc.

Another approach I personally have been using more recently is this: give a 
single recipient a domain and deliver email to any address within that 
domain to the user.  If anyaddress at personaldomain.name is valid, the user 
quickly becomes trained to reject any incoming messages that aren't part of 
a known context.  At the same time, the recipient can use the context 
provided on all messages accepted to get visibility into how the sender 
obtained permission to communicate with them.  This has the benefits of 
challenge-response, but completely eliminates the need for challenges.  The 
only address I have is one I've given out, and those are generally dedicated 
to a specific context.  If you try to contact me within a fabricated 
context, I won't entertain it.

So, I start off with a clean slate with personaldomain.name.  I registered 
the domain with godaddy.com, so I tell them to contact me at 
godaddy.com at personaldomain.name.  I tell my mom that my email address is 
mom at personaldomain.name, Google uses google at personaldomain.name, ASRG uses 
asrg at personaldomain.name, etc.   At a point of critical mass, spammers would 
start social engineering and spam everyone at yahoo at personaldomain.name, 
assuming a majority of folks have a relationship with Yahoo.

When that happens, the user would just have to set a new context with that 
sender by changing their email address.  Fortunately, this does not impact 
any of the other senders with whom the user has established a communication 
context.  In this case, you could tell yahoo to use 
$0m#!p4$5w0rd.yahoo.com at personaldomain.name if you wanted to get really 
obscure about it.

Generally speaking, this is sort of a shared-secret approach with a unique 
context for each relationship.  The pain factor for both the sender and 
receiver to change the shared-secret is very low, because each sender has a 
unique shared-secret and the recipient can grant and revoke them at will. 
The pain factor for the spammer is high.  They have to find a valid context 
the recipient is willing to accept, and if they violate his or her concept 
of appropriate use of that context, they will find the context quickly 
revoked.

You don't need CAPTCHA to do this, and you don't have to bounce mail sent 
within an unknown or revoked context.  It is deliverable; the user just 
refuses to accept it.

----- Original Message ----- 
From: "Michael Kaplan" <mkaplansolution at lycos.com>
To: "Matt Schneider" <matt at spamhaus.org>
Cc: <asrg at ietf.org>
Sent: Sunday, December 05, 2004 2:21 PM
Subject: Re: [Asrg] Please critique my anti-spam system

Whitelisting in this context is completely new.

> - challenge/response is nothing new

This is not challenge/response, this is far superior.  I clearly contrast 
these two systems in my article.

> - if you want to not burden your friends with an initial
> challenge.. instead of spamming them to change the email address
> they have for you (still a burden) then why not add everyone in
> your address book to the "already passed the challenge procedure"
> list ?

The only people who ever need to decode a CAPTCHA are people who are not 
using a valid sub-ddress and who are not on the white list.

> - CAPTCHA assumes everyone using this system speaks English.

My CAPTCHA usuable across all languages.  People almost always communicate 
via email with people who can read the same language.  Correspond with 
someone who has Chinese as their default language and the instructions for 
the CAPTCHA will be in Chinese.  There are additional logical ways that the 
language issue will be addressed.


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