I had an interesting talk with a work buddy about his Master’s program which is Information Security. That led to a rambling discussion on what “trust” and “identity” mean. So what if access to a system was based on an Eliza-like conversation with the computer. There would be an initial “get acquainted” session, and then the “login” conversation would be shorter.

• Store key hit timing and error/correction  patterns as well as the words.
• Use a plagerism test to look for cut-and-paste replies from recorded sessions
• Login discussions could be like Capchas in that they could be half test, half learning.