@misc{cryptoeprint:2013:595,
author = {Mark D. Ryan},
title = {Enhanced certificate transparency and end-to-end encrypted mail},
howpublished = {Cryptology ePrint Archive, Report 2013/595},
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.