@misc{cryptoeprint:2013:418,
author = {Nils Fleischhacker and Tibor Jager and Dominique Schröder},
title = {On Tight Security Proofs for Schnorr Signatures},
howpublished = {Cryptology ePrint Archive, Report 2013/418},
year = {2013},
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.