@misc{cryptoeprint:1996:004,
author = {Ronald Cramer and Ivan Damgaard},
title = {Linear Zero-Knowledge - A note on Efficient Zero-Knowledge Proofs and Arguments},
howpublished = {Cryptology ePrint Archive, Report 1996/004},
year = {1996},
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.