@misc{cryptoeprint:2011:104,
author = {Colleen M. Swanson and Douglas R. Stinson},
title = {Unconditionally Secure Signature Schemes Revisited},
howpublished = {Cryptology ePrint Archive, Report 2011/104},
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.