Tor: Design
The Design Document (published at Usenix Security 2004) gives our justifications and security analysis for the Tor design:
The Specification aims to give developers enough information to build a compatible version of Tor:
Look at the slides from the Codecon 2004 talk, or listen to the audio from the talk. You can also peruse the Black Hat 2004 slides or Defcon 2004 slides.
The list of stuff the developers know they need to do