No Spam at Any CPU Speed

1
No Spam at Any (CPU) Speed

• Mike Burrows
• Cynthia Dwork
• Andrew Goldberg
• MSR Silicon Valley

2
Computational Spam Fighting

• If I dont know you
• Prove you spent ten seconds computing,
• just for me, and just for this message
• User Experience
• Automatically and in the background
• Checking proof extremely easy
• Proof is solution to crypto puzzle
• Memory latencies more uniform than cpu speeds
• Factor of 15 versus factor of 5
• Design puzzles requiring many random memory
  accesses

3
Point-to-Point Architecture(Ideal Message Flow)
m, tag f(S,R,date,nonce)
Sender client S
Recipient client R

• (Ideal Message Flow)
• Send and forget
• Cache tags, discard duplicates one puzzle buys
  one message

4
Here to There (and There)
m
Ignorant Sender S
Spam-Protected Recipient R
bounce
release m

• Three e-mail messages
• Rs mail client caches m, S, R, t, nonce
• Bounce (viral marketing opportunity)
• html attachment with Java Script for f
• contains parameters for f (S, R, t,nonce)
• clicking on link causes computation, sending
  e-mail
• (optional) link for download of client software

5
Run Times

• Machine Time x/IBM CPU
• IBM Server 10.6 1.0 1.3 GHz
• P3 Laptop 11.0 1.04 1.2 GHz
• P4 Laptop 14.3 1.25 2.0 GHz
• Mac Laptop 17.4 1.64 800 MHz
• P2 Desktop 23.8 2.24 366 MHz
• Sun Server 25.5 2.41 450 MHz
• Set-top 48.4 4.57 233 MHz
• PDA 53.6 5.06 200 MHz
• Time total time to solve puzzle
• x/IBM ratio to IBM Server of solution speed

6
One Implementation Proxies
P R O X Y
P R O X Y
Sender Client
Receiver Client
Server
Server

• Sender Proxy computes tags
• Receiver Proxy checks tags
• wrongly tagged mail placed in special folder
  and/or bounced
• bounce message can contain link to code download
  site
• Other possibilities include built-in
  functionality
• eg in Outlook/Exchange, Hotmail