Dramatis Personae

When talking about cryptography, we often use a standard cast of characters

Alice, Bob, Carol, Dave
People (usually honest) who wish to communicate

Eve
A passive eavesdropper, who can listen to any trasmitted messages

Mallory
An active Man-In-The-Middle, who can listen to, and modify, insert, or delete, transmitted messages

Trent
A Trusted Third Party