@misc{cryptoeprint:2009:635,
author = {Kazukuni Kobara},
title = {Flexible Quasi-Dyadic Code-Based Public-Key Encryption and Signature},
howpublished = {Cryptology ePrint Archive, Report 2009/635},
year = {2009},
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.