Physical Keys

A physical key is an object whose characteristics are somehow secret, and which is usually somewhat difficult to reproduce. It could be:

• a piece of machined metal that unlocks the computer;
• a hardware device that attaches to an I/O channel (e.g., a serial line with an RS-232 connector), which can be interrogated by the system, and which must be present to execute certain programs;
• a smart card, which is a credit-card-sized circuit board which contains some form of non-volatile memory, and may even have a CPU.

• keys can be forgotten, broken, lost, borrowed or lent;
• keys can be stolen, or copied (by a determined user);
• keys and compromised locks can be expensive to replace;
• it can be difficult or impossible to automatically or remotely revise authorizations associated with a particular physical key.
• physical keys must be physically managed, i.e., stored, logged, kept secure, etc.