The mid-1990ssaw an exciting convergenceof a number of dieren t information protection technologies, whose theme was the hiding (as opposed to encryption) of information. Copyright marking schemes are about hiding either copyright notices or individual serial numbers imperceptibly in digital audio and video, as a component in intellectual property protection systems; anonymous c- munication is another area of rapid growth, with people designing systems for electronic cash, digital elections, and privacy in mobile communications; se- rity researchers are also interested in 'stray'...