@misc{cryptoeprint:2011:564,
author = {N. Ahmed and C.D. Jensen and E. Zenner},
title = {Private-key Symbolic Encryption},
howpublished = {Cryptology ePrint Archive, Report 2011/564},
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.