@misc{cryptoeprint:2013:415,
author = {Ciaran Mullan and Boaz Tsaban},
title = {Short collision search in arbitrary SL2 homomorphic hash functions},
howpublished = {Cryptology ePrint Archive, Report 2013/415},
year = {2013},
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.