Suratose Tritilanunt Colin Boyd Ernest Foo Juan Manuel González Nieto Toward Non-parallelizable Client Puzzles. 247-264 2007 conf/cans/2007 CANS http://dx.doi.org/10.1007/978-3-540-76969-9_16 db/conf/cans/cans2007.html#TritilanuntBFN07