Cloudera : Learn Authentication with Kerberos in Hadoop

Course details

The Kerberos protocol relies heavily on an authentication technique that makes use of shared secrets. The basic concept is quite simple: If a secret is known by only two people, either person can verify the identity of the other by confirming that the other person knows the secret.

For example, let's suppose that Alice often sends messages to Bob and that Bob needs to be sure that a message from Alice really has come from Alice before he acts on its information. They decide to solve their problem by selecting a password, and they agree not to share this secret with anyone else. If Alice's messages can somehow demonstrate that the sender knows the password, Bob knows that the sender is Alice.

The only question for Alice and Bob to resolve is how Alice can show that she knows the password. She might simply include it somewhere in her messages, perhaps in a signature block at the end — Alice, Our$ecret . This would be simple and efficient and might even work if Alice and Bob can be sure that no one else is reading their mail. Unfortunately, that is not the case. Their messages pass over a network used by people like Carol, who has a network analyzer and a hobby of scanning traffic in hope that one day she might spot a password. So it is out of the question for Alice to prove that she knows the secret simply by saying it. To keep the password secret, she must show that she knows it without revealing it.

The Kerberos protocol solves this problem with secret key cryptography . Rather than sharing a password, communication partners share a cryptographic key. They use knowledge of this key to verify one another's identity. For this method of authentication to work, the shared key must be symmetric — a single key must be capable of both encryption and decryption. One party proves knowledge of the key by encrypting a piece of information, the other by decrypting it.