Data Encryption Standard(DES)
A slecture on Cryptography by student Divya Agarwal and Katie Marsh
Partly based on the Summer 2015 lecture material of Prof. Paar.
The lecture video below by Prof. Paar, talks about the history of DES and gives a basic understanding of DES.
Contents
Link to video on youtube
Accompanying Lecture Notes
Introduction
- DES is a block cipher and as the name suggests it works on blocks of bits or binary numbers--the 0s and the 1s common to digital world. It encrypts group of 64 plaintext bits(one block) and returns 64 ciphertext bits. To do the encryption, DES uses keys which are also 64 bits long. However, every 8th key bit is ignored in the DES algorithm, so that the effective key size is 56 bits.
Block Cipher Primitives
The lecture video below by Prof. Paar, talks about the Confusion and Diffusion in Block Ciphers.
Link to video on youtube
- Confusion : An encryption operation where the relationship between plaintext and ciphertext is obscured. Today, a common element for achieving confusion is substitution, which is found in both AES and DES.
- Diffusion : An encryption operation where the influence of one plaintext symbol is spread over many ciphertext symbols with the goal of hiding statistical properties of the plaintext. A simple diffusion element is the bit permutation, which is frequently used within DES.
Both operations by themselves cannot provide security. The idea is to concatenate confusion and diffusion elements to build a more secure cipher.
References
- C. Paar. Understanding Cryptography. Lecture Notes. Dept. of Electr. Eng. and Information Sciences, Ruhr University.
- C. Paar and J. Pelzl. Understanding Cryptography. A textbook for Student and Practitioners. Springer 2010.
Questions and comments
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