Page 378 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

FIGURE 6.2 The magic door

Victor can stand at the entrance to the cave and watch Peggy depart
down the path. Peggy then reaches the door and opens it using the

password. She then passes through the door and returns via path 2.
Victor saw her leave down path 1 and return via path 2, proving that
she must know the correct password to open the door.

Split Knowledge

When the information or privilege required to perform an operation is
divided among multiple users, no single person has sufficient
privileges to compromise the security of an environment. This

separation of duties and two-person control contained in a single
solution is called split knowledge. The best example of split knowledge
is seen in the concept of key escrow. Using key escrow, cryptographic
keys, digital signatures, and even digital certificates can be stored or
backed up in a special database called the key escrow database. In the
event a user loses or damages their key, that key can be extracted from