Luis Sequeira
Luis Sequeira is an IT professional with experience in cloud environments, quality of service and network traffic analysis, who loves looking for solutions to engineering challenges, share knowledge. At work, the main challenge is to integrate different network and software technologies to provide solution in a wide range of areas, e.g., virtual network functions, machine learning, autonomous driving, robotics and augmented reality.
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 of the state matrix ([a00]) is divided into two groups of four bits each one and they are used as pointers to the S-Box rows and columns, respectively, for replacement, in Figure # 1 is shown how the value 19 will be replaced by d4.
Figure # 1: S-Box use [1].
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 telecommunications network of an ISP (Internet Service Provider) is actually an interaction of various networks types, within LTE (4G) can be highlighted as an access network to the end user. The information flow reaches to the user through several infrastructures, on which the ISP carries data traffic, from this perspective, some necessary points will be discussed in order to ensure the Quality of Service (QoS) in such environments.
From the point of view of LTE management, it is permitted to define profiles and classes of services, which are key points when negotiating QoS mobile requirements during the communication establishment, the transit of packets, even in handovers. However, it is necessary to consider the access and transport network if we want to ensure end-to-end QoS.
Transport Network
A typical scenario of an Internet service provider could be described as shown in Figure # 1, it can be seen that LTE is only a part of the provider's access network. The ISP has different types of access networks depending on the provided services. All the necessary infrastructure to transport information from the access networks, must transit through the core network. The core is also connected with other different network types, where the end service is usually located (Internet, PSTN, ftp services, video streaming, voice or other), which the user wants to access.
Figure # 1. ISP's simplified topology [2].