@misc{cryptoeprint:2014:563,
author = {Aleksandar Kircanski},
title = {Analysis of Boomerang Differential Trails via a SAT-Based Constraint Solver URSA},
howpublished = {Cryptology ePrint Archive, Report 2014/563},
year = {2014},
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.