1. DES: Data Encryption Standard
Introduction
Background
How It Works
Examples
Cracking

2. DES: Data Encryption Standard Introduction
The DES (Data Encryption Standard) algorithm is the most widely used encryption algorithm in the world.
Used in government and banking
Used from
Has a version called “Triple-DES."
Triple DES you use three DES encryptions with three separate keys.
Managing three keys is more difficult

3. DES: Data Encryption Standard Background
In 1972 the NIST decides to assist in the development of a secure method
NIST was called the National Bureau of Standards
May 15, 1973 NBS published a notice in the Federal Register soliciting proposals for cryptographic algorithms to protect data during transmission and storage
It received none until August 6, 1974 from IBM
The NSA and the NIST National Institute of Standards and Technology played a substantial role in the final stages of developing DES.

4. DES: Data Encryption Standard Background
The NBS adopted a modification of the IBM LUCIFER algorithm as the new Data Encryption Standard (DES) on July 15, 1977
DES was quickly adopted for non-digital media, such as voice-grade public telephone lines.
The banking industry, which is the largest user of encryption outside government, adopted DES as a wholesale banking standard.

5. DES: Data Encryption Standard Background
Originally developed by IBM researcher Horst Feistel
Feistel wanted to call the system Dataseal
IBM shortened the term demonstration cipher to Demon
Demon morphed in to the name LUCIFER
The NIST re-certified DES every five years
AES (Advanced Encryption Standard) replaces DES in October 2000 Rihndael.

6. DES: Data Encryption Standard How it Works
Input key for DES is 64 bits long, the actual key used by DES is only 56 bits in length
DES has a 64-bit block size
DES is a 16-round Feistel cipher
Originally designed for implementation in hardware.
Uses transposition and substitution
Computer memory made it possible for Feistel to use transposition in his system

7. DES: Data Encryption Standard How it Works
It is a single-key cryptosystem, when used for communication both sender and receiver must know the same secret key which can be used to encrypt or decrypt the message.
DES can also be used by a single-user, for example to store files on a hard disk securely.

8. DES: Data Encryption Standard How it Works
DES works on bits, or binary numbers--the 0s and 1s common to digital computers.
Each group of four bits makes up a hexadecimal, or base 16, number.
Binary "0001" is equal to the hexadecimal number "1“

9. DES: Data Encryption Standard How it Works
Binary
Hex
0001 1
1001 9
0010 2
1010 A
0011 3
1011 B
0100 4
1100 C
0101 5
1101 D
0110 6
1110 E
0111 7
1111 F
1000 8
0000

10. DES: Data Encryption Standard How it Works
DES works by encrypting groups of 64 message bits, which is the same as 16 hexadecimal numbers 4 x 16 = 64.
To do the encryption, DES uses "keys" where are also apparently 16 hexadecimal numbers long, or apparently 64 bits long.
However, every 8th key bit is ignored in the DES algorithm, so that the effective key size is 56 bits.

11. DES: Data Encryption Standard How it Works
For example
take the plaintext message " "
Encrypt it with the DES key "0E329232EA6D0D73",
End up with the ciphertext " “
If the ciphertext is decrypted with the same secret DES key "0E329232EA6D0D73“
The result is the original plaintext " "

12. DES: Data Encryption Standard How it Works
For example
the plaintext message
" “
1000, 0111, 1000, 0111,
1000, 0111, 1000, 0111
4 x 16 = 64 Bits

13. DES: Data Encryption Standard How it Works
For example
The Key: Drop every eight bit
"0E329232EA6D0D73”
0000, 1110, 0011, 0010,
1001, 0010, 0011, 0010,
1110, 1010, 0110, 1101,
0000, 1101, 0111, 0011
4 x = 56 Bits

14. DES: Data Encryption Standard How it Works
DES works by encrypting groups of 64 message bits, which is the same as 16 hexadecimal numbers 4 x 16 = 64.
To do the encryption, DES uses "keys" where are also apparently 16 hexadecimal numbers long, or apparently 64 bits long.
However, every 8th key bit is ignored in the DES algorithm, so that the effective key size is 56 bits.

15. DES: Data Encryption Standard Cracking
No easy attack on DES has yet been discovered, despite research efforts over many years.
There is no feasible way to "break" DES other than an exhaustive search - a process which takes 255 steps on average.
Cryptanalysis methods which rely on knowledge of some of the plaintext have had some success.

16. DES: Data Encryption Standard Cracking
RSA issues the DES Challenge
1997 Rocke Verser recovered the secret key in 96 days.
1998 Distributed.net cracked DES in 41 days
In July 1998 EFF Electronic Frontier Foundation used a $220,000 machine to crack DES
This device cracked DES in 56 hours
1999 cracked DES in less than 24 hours