The document summarizes the Data Encryption Standard (DES) encryption algorithm. It discusses how DES uses confusion and diffusion techniques with permutations and XOR operations. It describes how DES originated from a 64-bit block cipher developed by IBM in 1971 that was adopted as a standard by the NSA in 1977. It then outlines the basic steps of DES encryption, which includes an initial permutation, 16 rounds of encryption using 48-bit keys, a left-right swap, and a final permutation. The decryption process reverses the order of these steps.

1. Lec-7: Data Encryption Standard
Mr. Islahuddin Jalal
MS (Cyber Security) – UKM Malaysia
Research Title – 3C-CSIRT Model for Afghanistan
BAKHTAR UNIVERSITY ‫باخترپوهنتون‬ ‫د‬

2. Symmetric and Asymmetric
Encryption Algorithms

3. What is DES?
Symmetric Key algorithm for Encryption

4. DES - Basics
 DES uses the two basic techniques of cryptography -
confusion and diffusion.
 At the simplest level, diffusion is achieved through numerous
permutations and confusion is achieved through the XOR
operation.

5. History of DES
In 1971, IBM developed an algorithm,
named LUCIFER which operates on a block
of 64 bits, using a 128-bit key
Walter Tuchman, an IBM researcher,
refined LUCIFER and reduced the key size
to 56-bit, to fit on a chip.

6. History of DES
In 1977, the results of Tuchman’s project of
IBM was adopted as the Data Encryption
Standard by NSA (NIST).

7. How Data Encryption Standard (DES) work?

8. Illustration of DES algorithm
• There are four Steps involved in the DES
1. Initial Permutation (IP)
2. 16 Feistal Rounds
3. Left right Swapping
4. Final Permutation (FP) which is reverse permutation (IP- )

9. 64-bit
64-bit

10. What is done inside F function?

11. How Expansion is done?

12. 0 1 1 0 0 1 0 1
K0
R0L0
K1
R1L1
Kn
Rn Ln XOR f(Kn,Rn)
Li+1 = Ri
Ri+1 = Li XOR f ( Ri , Ki )
C = (Rn+1,Ln+1)
m
C

13. Decryption
• The same algorithm as
encryption.
• Reversed the order of key
(Key16, Key15, … Key1).
• For example:
• IP undoes IP-1 step of
encryption.
• 1st round with SK16 undoes
16th encrypt round.
[1]

14. 0 1 1 0 0 1 0 1
Kn
Kn-1
Rn-1Ln-1
K0
L0 R0
Ri = Li+1
Li = Ri+1 XOR f ( Li+1, Ki )
m = (L0 , R0)
Ln XOR f(Kn,Rn)
c
m

15. Thank You
For Your Patience