@misc{cryptoeprint:2005:210,
author = {John Black},
title = {The Ideal-Cipher Model, Revisited: An Uninstantiable Blockcipher-Based Hash Function},
howpublished = {Cryptology ePrint Archive, Report 2005/210},
year = {2005},
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.