@misc{cryptoeprint:1998:015,
author = {Shai Halevi and Silvio Micali},
title = {More on Proofs of Knowledge},
howpublished = {Cryptology ePrint Archive, Report 1998/015},
year = {1998},
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.