A. Launch codes for Titan II nuclear missiles were stored in this safe. The two-person launch team had to work together to unlock the codes and launch the missile; neither could launch the missile independently.

B. This is the rationale behind Unix sudo and Windows User Account Control, both of which allow users to temporarily apply administrative rights to perform a privileged task instead of being continuously enabled.

C. Even the US National Security Agency, which resisted open crypto designs for decades, now uses the Advanced Encryption Standard (AES) to encrypt classified information. Unlike the previous encryption standard the US government adopted, AES was refined using an open process that published the results of the tests and analyses that led to its selection.

D. A classic example arises when two weakly shielded audio cables are bundled together: a loud signal on one might leak into the other, creating noise or even broadcasting the other cable's signal. Similar covert channels might arise when separate processes execute with shared CPU, RAM, or I/O resources.

E. Passwords fail this principle: users have been harangued for decades about picking hard-to-guess passwords, not sharing them, not using the same one in multiple places, and so on. User surveys and security breaches repeatedly illustrate that many people don't follow those recommendations.