Ove Scavenius Martin Boesgaard Thomas Pedersen Jesper Christiansen Vincent Rijmen Periodic Properties of Counter Assisted Stream Ciphers. 39-53 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2964&spage=39 2004 conf/ctrsa/2004 CT-RSA db/conf/ctrsa/ctrsa2004.html#ScaveniusBPCR04