The development of VoIP (Voice over Internet Protocol) technologies have been widely accepted by companies seeking lower costs for voice communications mainly in SMEs (Small and Medium Enterprises) environments. The term VoIP should not be confused with ToIP (Telephony over IP), VoIP refers to the technology required for voice communication over IP, while ToIP is a telephone service for users, which uses VoIP technology to give such service. VoIP allows voice transmission via an IP network, including those connected to the Internet. It involves digitizing voice signals, via a codec. The bandwidth consumption of such communication is directly related to…

Some time ago, I read an interesting article of a "successful attack" against AES, the famous symmetric-key algorithm. Raphael C.-W. Phan [1] presented a seven rounds "impossible differential attack" for AES-192 and AES-256. Someone may ask: what kind of attack is this?, well, it is a crypt-analysis that takes advantage of the differences that are impossible to be, in a data block through encryption, in order to discover the key?. Without going into many details of the method used, below I comment some of the most important results of this study. The attack involves taking pairs of identical texts in…

Package managers are tools to automate the process of installing, upgrading, uninstalling or configuring software on Linux. Package managers are part of the operating system and they use a single database for installation and a single packet format, for example: rpm or deb. They are also responsible for checking the digital signature, and dependency resolution for updates.

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.