Linux is a multiuser and multitasking operating system, ie, multiple users can work on the system simultaneously running several tasks at once. It is therefore, very important that the operating system allows the management and control of users.

Unix based systems organize all this by users and groups, where each user must be identified with a user name and password. During login, the password entered by each user, is encrypted and compared to the encrypted passwords that were previously stored in the system.

As we mentioned in a previous article, rounds that make up the AES algorithm can be divided into three different categories: initial rounds, standard round and final round. When encryption, the information is subjected to a different number of rounds (10, 12 and 14 respectively) in each case depending on the length of the key (128, 192 and 256 respectively). Each such round is made up of combinations of transformations, the possible transformations include: ByteSub, ShiftRow, MixColumns and AddRoundKey. Figure # 1 shows the relationship of the transformation and corresponding rounds.

Figure # 1: Distribution of the transformations in each round.

In order to perform estimations of a traffic model for multimedia flows, it is necessary for the researcher to have precise control of the test environment, minimizing errors and interference that may occur, leaving a test scenario that allows a smooth development to the application to be modeled. As an example, we have selected a VoIP traffic which is quite easy to interpret and it provides some of the things that must be done.

Scenario for testing

Figure # 1 shows the diagram used for testing in order to obtain the pattern of traffic on the transmission of voice over IP is shown. In this case, we use a voice over IP gateway Linksys SPA 3102, with the aim of connecting a conventional telephone system with an IP network. A sniffer can capture traffic using the network for later analysis.

Figure # 1: Scenario used to determine the voice traffic.