Cryptology ePrint Archive: BibTeX Citation of Report 2011/123

@misc{cryptoeprint:2011:123,
    author = {Andrey Bogdanov and Vincent Rijmen},
    title = {Linear Hulls with Correlation Zero and Linear Cryptanalysis of Block Ciphers},
    howpublished = {Cryptology ePrint Archive, Report 2011/123},
    year = {2011},
    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.