@misc{cryptoeprint:2002:161,
author = {Jan Camenisch and Victor Shoup},
title = {Practical Verifiable Encryption and Decryption of Discrete Logarithms},
howpublished = {Cryptology ePrint Archive, Report 2002/161},
year = {2002},
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.