Roger Dingledine and Paul Syverson have a recent paper on reputations for MIX cascades which may be of interest, given previous discussions on how to build more reliable remailers.
See it at http://www.freehaven.net/doc/casc-rep/casc-rep.ps http://www.freehaven.net/doc/casc-rep/casc-rep.pdf slides at http://www.freehaven.net/doc/casc-rep/slides-oreilly.ps In case you saw the earlier paper by Dingledine, Freedman, Hopwood, and yours truly, this paper is for MIX cascades (as opposed to free picked routes) and removes the need for trusted "witnesses." -David
