Zmail : Zero-Sum Free Market Control of Spam

1
Zmail Zero-Sum Free Market Control of Spam
Benjamin J. Kuipers, Alex X. Liu, Aashin
Gautam, Mohamed G. Gouda
2
Spam Problem

• Volume of Spam
• 2001 8 of all email traffic was spam
• 2004 60 of all email traffic was spam
• emails per day 31 billion (60 spam 18.6
  billion)
• spam emails per person per day 6
• Cost of Spam
• 2003 10 billion/year in U.S. (Ferris Research)
• 20.5 worldwide (Radicati
  Group)
• Just cost for adding spam processing servers

3
Anti-Spam Legal Approaches

• Punish spammers by anti-spam laws
• Problems
• Hard to define spam
• First Amendment Right to Free Speech
• Hard to enforce anti-spam laws
• Spammers move to another country

4
Anti-Spam Filtering Approaches

• Filter out spam based on text content
• Problems
• False Positive
• What if a job offer email gets filtered?
• Can be foiled by spammers
• For example, imbedding spam text in images

5
Anti-Spam Economic Approaches

• Require senders to pay something
• Human Effort Sender pays human effort
• Inconvenient
• Inefficient
• Challenge can be perceived as rude
• Computational Cost Sender pays CPU time
• Inefficient

6
Anti-Spam Zmail

• Current cost for spamming is almost zero
• Users attention is the important resource
  consumed
• Basic idea of Zmail
• The sender of an email pays money directly to the
  receiver.
• Zero sum (unlike USPS)
• The amount of money charged to the sender
• The amount of money rewarded to the receiver
• The money earned can be used to send email.
• The cost of sending one email is a unit called an
  e-penny.

7
Impact of Market Forces

• Spammers
• Cost of spamming significantly increases
• Bulk email advertising become more targeted
• Normal Users
• Most users receive more email than they send
• If not, pay money or subscribing commercial
  email
• ESPs (Email Service Providers)
• Less spam, less bandwidth, less computational
  cost

8
Zmail Architecture
User
User
User
ESP
User
User
ESP
ESP
User
User
User
User
Bank
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The Zmail Protocol two parties

• Bank
• Each compliant ESP has an account with bank
• Manage accounting for compliant ESPs
• ESP buy and sell e-pennies with bank
• Exchange e-pennies between real money for ESPs
• ESPs
• Manage accounting for each of its users
• Users buy and sell e-pennies with their ESPs

10
The Zmail Protocol Email Transfer

• An email user s of ESP A ? user r of ESP B
• Sending
• A reduces ss balance by one
• A records that A owes B one more e-penny
• Receiving
• B increments rs balance by one
• B records that A owes B one more e-penny

11
The Zmail Protocol Misbehavior Detection

• What if an ESP lies?
• Periodically, every ESP reports to the bank how
  much they owe to every other ESPs
• Misbehavior Detection
• A says that A owes B x e-pennies
• B says that A owes B y e-pennies
• If x ! y, then Bank further investigates who
  lies.
• Most ESPs are honest.

12
Mailing Lists

• List server email distributor subscriber DB
• A subscriber sends an email to distributor,
  distributor forwards the email to everyone
• Solution for each email from distributor,
  receivers ESP sends back an ack email.
• Extra benefit subscriber DB is always updated

13
Zombies and Email Viruses

• Zombie sends out spam at users expense
• Virus sends email to everyone in address book
• Solution each user specify a limit on the number
  of email that he can send a day.
• Extra benefit detecting virus and zombies

14
Incremental Deployment

• Zmail runs on top of SMTP
• No change to SMTP
• Deployment starting from two compliant ESPs
• A user may decide to segregate, filter, or
  discard email from non-compliant ESPs.

15
Bank Setup

• Internet already has some central authorities
  such as IANA that controls IP assignment

16
Conclusions

• Zmail gives no free ride to spammers
• Zmail requires no definition of spam
• Zmail works with other anti-spam techniques
• Zmail can be incrementally deployed