@misc{cryptoeprint:2004:036,
author = {Yan-Cheng Chang},
title = {Single Database Private Information Retrieval with Logarithmic Communication},
howpublished = {Cryptology ePrint Archive, Report 2004/036},
year = {2004},
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.