DES (Data Encryption Standard) is called as the symmetric key algorithm that encrypts the electronic data key.
HMAC Hash Message Authentication Code is a code that involves cryptographic hash function in combination with the secret cryptographic key. The cryptographic strength of HMAC depends on the size of the secret key used. These codes are substantially less affected by collisions.
So far no known extension attacks have been found against HMAC because the outer application of the hash function masks the intermediate results of the internal hash.
CHAP Challenge Handshake Authentication Protocol (CHAP) is a scheme used by Point to Point protocol. This protocol authenticates the identity of the remote clients by using the 3 way handshake. As soon as the link is established, the authenticator sends a “challenge” message to the peer. The peer will then respond with the calculated value that is generated using one-way hash function. The authenticator checks the response against its own calculated yet expected value. If the value matches, the authenticator acknowledges the authentication, otherwise the connection will be terminated.