2.8.3 Authentication in distributed systems: Private Key Encryption

In distributed systems, the network between the machine on which the password is typed and the machine the password is authenticating on is accessible to everyone.

Two roles for encryption:

1. Authentication - do we share the same secret?
2. Secrecy - I don't want anyone to know this data (eg medical records)

Use an encryption algorithm that can easily be reversed given the correct key, and difficult to reverse without the key

• From cipher text, can't decode without password.
• From plain text and cipher text, can't derive password.
• As long as the password stays secret, we get both secrecy and authentication.