@misc{cryptoeprint:2005:212,
author = {Joan Daemen and Vincent Rijmen},
title = {Probability distributions of Correlation and Differentials in Block Ciphers},
howpublished = {Cryptology ePrint Archive, Report 2005/212},
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.