@misc{cryptoeprint:2005:324,
author = {Nicolas G\"urel},
title = {Extracting bits from coordinates of a point of an elliptic curve},
howpublished = {Cryptology ePrint Archive, Report 2005/324},
year = {2005},
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.