When you receive a Zephyr windowgram, the message is marked Authentic, UNAUTHENTIC, or FORGED. These labels indicate the result of the sender's or your own authentication.
To make a long story short, it is possible to fool your workstation and make it believe you are somebody else. For this reason Project Athena has developed a system called Kerberos. Kerberos is able to verify that you are who you say you are, and not impersonating someone else. Zephyr uses the Kerberos system to authenticate its users.
If you and the sender pass authentication, then the message is marked "Authentic." If you OR the sender fails authentication, then the message is marked "UNAUTHENTIC." This does not necessarily mean that something bad is occurring. Any user can fail authentication if he loses his 'Kerberos tickets', or if his tickets expire (which they do after 10 hours). You can gain a new set of tickets at any time by running the 'renew' program. After typing 'renew', you will be prompted to enter your password.
FORGED is a special case whereby you had valid Kerberos tickets, but the information in the tickets did not match that of the original tickets used by Zephyr. In an extreme case, it might indicate someone having tampered with the Kerberos tickets, but most commonly, it occurs when you obtain new tickets, and thus these tickets do not concur with those which Zephyr is expecting. If this is the case, it can be fixed by:
Zephyr will then receive the new tickets.