@misc{cryptoeprint:2000:020,
author = {Maria Isabel Gonzalez Vasco and Igor E. Shparlinski},
title = {On the Security of Diffie--Hellman Bits},
howpublished = {Cryptology ePrint Archive, Report 2000/020},
year = {2000},
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.