Kerberos depends on Secret Keys or Symmetric Key cryptography.

Kerberos a third party authentication protocol. It was designed and developed in the mid 1980's by MIT. It is considered open source but is copyrighted and owned by MIT. It relies on the user's secret keys. The password is used to encrypt and decrypt the keys.

This question asked specifically about encryption methods. Encryption methods can be SYMMETRIC (or secret key) in which encryption and decryption keys are the same, or ASYMMETRIC (aka 'Public Key') in which encryption and decryption keys differ.

'Public Key' methods must be asymmetric, to the extent that the decryption key CANNOT be easily derived from the encryption key. Symmetric keys, however, usually encrypt more efficiently, so they lend themselves to encrypting large amounts of data. Asymmetric encryption is often limited to ONLY encrypting a symmetric key and other information that is needed in order to decrypt a data stream, and the remainder of the encrypted data uses the symmetric key method for performance reasons. This does not in any way diminish the security nor the ability to use a public key to encrypt the data, since the symmetric key method is likely to be even MORE secure than the asymmetric method.

For symmetric key ciphers, there are basically two types: BLOCK CIPHERS, in which a fixed length block is encrypted, and STREAM CIPHERS, in which the data is encrypted one 'data unit' (typically 1 byte) at a time, in the same order it was received in.

The following answers are incorrect:

Public Key cryptography. Is incorrect because Kerberos depends on Secret Keys or Symmetric Key cryptography and not Public Key or Asymmetric Key cryptography.

El Gamal cryptography. Is incorrect because El Gamal is an Asymmetric Key encryption algorithm.

Blowfish cryptography. Is incorrect because Blowfish is a Symmetric Key encryption algorithm.

References:

OIG CBK Access Control (pages 181 - 184)

AIOv3 Access Control (pages 151 - 155)

Wikipedia http://en.wikipedia.org/wiki/Blowfish_%28cipher%29 ; http://en.wikipedia.org/wiki/El_Gamal

http://www.mrp3.com/encrypt.html