There are proof of concepts to keep the key in registers, for example http://www1.informatik.uni-erlangen.de/tresor http://www1.informatik.uni-erlangen.de/treso

There are proof of concepts to keep the key in registers, for example http://www1.informatik.uni-erlangen.de/tresor http://www1.informatik.uni-erlangen.de/tresor That prevents coldboot attacks and other means of reading the key out of memory.