Jens Groth Cryptography in Subgroups of Z<sub>n</sub>. 50-65 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3378&spage=50 2005 conf/tcc/2005 TCC db/conf/tcc/tcc2005.html#Groth05