Question 21

Assume Alice and Bob are physically far apart. Each has a padlock and a key to their own padlock. Alice wants to send a message to Bob securely through the mail, but neither Alice nor Bob wish to share their padlock keys with anyone (including each other). Alice has a box which has two places it can be locked with padlocks, and if either is locked then the box is secure. Explain the process they use step by step.

* (4 pts) Answer:

21) Performing this process using actual encryption requires a commutative cypher (an encryption process where the order of applying encryption / decrpytion using multiple encryption keys does not matter) ? why is this necessary for this process to work?

* (2 pts) Answer: