You have to choose the cryptographic algorithms for a KDC where two different classes of encryption occur: ekU,KDC (), where U denotes an arbitrary network node (user), ekses() for the communication between two users. You have the choice between two different algorithms, DES and 3DES (TripleDES), and you are advised to use distinct algorithms for both encryption classes.

Which algorithm do you use for which class? Justify your answer including aspects of security as well as celerity.

Answer:

To choose algorithms among the two different cryptographic algorithms, then first need to know the difference between the DES and 3DES.

In DES algorithm, to encrypt the message it uses 56-bit key that is of 7 characters long. So, to encrypt a simple plain text it uses only one key to encrypt the message of 56-bits.

To decrypt the message the same is used to decrypt the message.

This is clear that it can be decrypted easily by the third party.

Now, in 3DES algorithm, to encrypt the message it uses totally of 168-bits that is, it uses three 56-bits DES keys to encrypt a message. With the first key it encrypts the text. By using second 56-bit DES key to decrypt the encrypted text and scrambles the text. Finally, the third 56-bit DES key is used to encrypt the scrambled decrypted text at second level.

Thus, by using 3DES algorithm, it makes the simple plain text more secure when compared to DES algorithm.

By using the above information, it is clear that over the network communication, the data has to be more secure. So, for ekU, KDC() the 3DES algorithm is used. For the communication between the two users, DES algorithm can be used. So, for ekses() the DES algorithm can be used.

Therefore, for ekU,KDC(), 3DES is used and for ekses(), DES is used.