@misc{cryptoeprint:2009:275,
author = {Thomas Dullien},
title = {Algebraic Attacks specialized to \(\mathbb{F}_2\) (Diplomarbeit)},
howpublished = {Cryptology ePrint Archive, Report 2009/275},
year = {2009},
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.