@misc{cryptoeprint:2011:276,
author = {Stephen C. Williams},
title = {Analysis of the SSH Key Exchange Protocol},
howpublished = {Cryptology ePrint Archive, Report 2011/276},
year = {2011},
note = {\url{http://eprint.iacr.org/}},
}
You will need the url.sty package (comes with most LaTeX installations) for the last line. Otherwise, remove the \url command.