The authentication protocol Kerberos allows a number of computers to prove their identity among them safely over an insecure network. The operation of the protocol is based on the Needham-Schroeder protocol, which defines a ''trusted third party'' called Key Distribution Center (KDC). William Stallings in his book Fundamentals of Network Security: Applications and Standards, Second Edition (p.394) defines a KDC as follows: Authorized system to transmit temporary session key for users. Each session key is transmitted encrypted using a master key that the Key Distribution Center shares with the target user. The KDC can be seen as a set of…

In Part I of the Overview of AES (Advanced Encryption Standard) the most relevant aspects of AES and S-Box was described. Now, we discuss some details of the so-called transformations (ByteSub, ShiftRow, MixColumns and AddRoundKey) and the subkey generation process. To see more details in a more dynamic way the Rijndael Animation application is recommended.   ByteSub This transformation performs a byte-by-byte substitution in each of the state matrix elements, ie, the state matrix [aij] is replaced by the matrix [Sij], Figure # 1 shows this process. Using Rijndael Animation [1] application, it can be seen as the first byte…

The AES (Advanced Encryption Standard) algorithm [1], known as Rijndael, was so-named by its creators Joan Daemen and Vincent Rijmen, it is the current international standard for communications encryption since october 2000. This algorithm is characterized by a symmetric block cipher with variable key length, the default key length is 128 bits but can also be set to 192 or 256 bits.

The symmetric-key cryptography, also called secret key cryptography, is a cryptographic method using the same key to encrypt and decrypt, ie, that the security of the algorithm is based on the key and not in algorithm. Examples of this type of cryptographic algorithms are: AES, DES, 3DES and RC5.