@misc{cryptoeprint:2011:588,
author = {Arpita Maitra and Goutam Paul},
title = {Another Look at Symmetric Incoherent Optimal Eavesdropping against BB84},
howpublished = {Cryptology ePrint Archive, Report 2011/588},
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.