Public Key Ecryption

For completeness we discuss the public key encryption in this lesson but you may skip this lesson as it doesn’t directly relate to Kerberos. However, bear in mind that Kerberos uses private/symmetric key encryption which is opposite of public/asymmetric key encryption in its theory and implementation.

Cryptographic algorithms can be classified as Symmetric and Asymmetric based on the number keys they use. The former use a secret key and the latter use a combination of secret and public keys.

Symmetric cryptographic algorithms use the same secret key to encrypt and decrypt. Asymmetric algorithms use two keys. The public key is used for encryption and the private or secret key is used to decrypt the message. Diffie and Hellman are acknowledged as the founders of asymmetric cryptography with the publication of their paper New Directions in Cryptography in 1976.

Asymmetric encryption overcomes two main problems of symmetric encryption.

1. The first is secure transmission of the key. Symmetric encryption uses the same key for encryption and decryption, so sharing the key secretly is of paramount importance. If the key is compromised then there is no point of encryption.

2. The second problem is key management. As the number of users increases, the number of keys increases rapidly as every pair needs a different key for private communication. Thus n users need ...