A Detailed Description of DES and 3DES Algorithms (Data Encryption Standard and Triple DES)
While many ciphers have been created based upon the Feistel structure, the most famous of these is the Data Encryption Standard (DES). DES was based off of the original Lucifer cipher developed by Feistel and Coppersmith and submitted as an entry to the US National Bureau of Standards as a candidate for the US official encryption standard. After some modification (to improve security against differential cryptanalysis), it was selected and published as a standard in 1977.
Encryption with DES
The DES algorithm is a 16-round Feistel cipher. It takes as input a 64-bit input and a 64-bit secret key, and consists of three main stages:
The initial permutation
The round function (repeated 16 times)
The final permutation
A diagram of how these stages fit together with the ...
Rijndael is a family of block ciphers developed by Belgian cryptographers Vincent Rijmen and Joen Daemen. It was submitted as an entry to the National Institute of Standards and Technology's (NIST) competition to select an Advanced Encryption Standard (AES) to replace Data Encryption Standard (DES). In 2001, Rijndael won the competition and the 128, 192, and 256-bit versions of Rijndael were officially selected as the Advanced Encryption Standard.
The three variants of AES are based on different key sizes (128, 192, and 256 bits). In this article, we will focus on the 128-bit version of the AES key schedule, which provides sufficient background to understand the 192 and 256 bit variants as well. At the end, we'll include a note the other variants, and how they differ from the 128-bit version.
Encryption with AES
The encryption phase of AES can be broken into three...
Sequence Motifs, Consensus Sequences and The Motif Finding Problem
Sequence Motifs and their Biological Significance
Sequence motifs are nucleic acid sequences that are widespread across or within a genomes and have or are speculated to have certain regulatory or structural biological functions.
Motifs that are found in different parts of the genomes like exons, introns and junk, have different functions. Motifs present in the exons ( coding part of the genome) decide the structure of the protein or label proteins to be sent to certain parts of the cell for processes like phosphorylation. Motifs that are present in introns (which makes up the non coding part of genome) are usually the regulatory sequences which determine the amount of gene expression and binding sites of proteins. Satellite DNA, which is the main component of centromeres and heterochromatin, is an example of motif found in junk parts of the genome.