Thomas Holenstein Ueli M. Maurer Johan Sjödin Complete Classification of Bilinear Hard-Core Functions. 73-91 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3152&spage=73 2004 conf/crypto/2004 CRYPTO db/conf/crypto/crypto2004.html#HolensteinMS04