@misc{cryptoeprint:2013:087,
author = {Namhun Koo and Gook Hwa Cho and Soonhak Kwon},
title = {Square Root Algorithm in F_q for q=2^s+1 (mod 2^(s+1))},
howpublished = {Cryptology ePrint Archive, Report 2013/087},
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.