@misc{cryptoeprint:2005:344,
author = {Tapan Rai},
title = {Countering chosen-ciphertext attacks against noncommutative polly cracker-type cryptosystems.},
howpublished = {Cryptology ePrint Archive, Report 2005/344},
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.