@misc{cryptoeprint:2015:576,
author = {Michael Scott and Brian Spector},
title = {The Carnac protocol -- or how to read the contents of a sealed envelope},
howpublished = {Cryptology ePrint Archive, Report 2015/576},
year = {2015},
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.