Chapter 7: Types of Symmetric Systems

•  Data Encryption Standard (DES)
• 3DES (Triple DES)
• Blowfish
• Twofish
•  International Data Encryption Algorithm (IDEA)
•  RC4, RC5, and RC6
• Advanced Encryption Standard (AES)
•  Secure and Fast Encryption Routine (SAFER)
•  Serpent

Data Encryption Standard:

History:

• 1974, IBM’s 128-bit algorithm (Lucifer) that was modified by the NSA (National Institute of Standards and Technology) to 64-bits which became a national cryptographic standard in 1977 and an American National Standards Institute (ANSI) standard in 1978.
• NSA announced that it would no longer endorse DES and DES-based products would no longer fall under compliance with Federal standard 1027 starting January 1988. This was not accepted well and eventually NSA extended the life of DES another 5 years.
• DES was eventually broken by Electronic Frontier Foundation who built a computer system that broke DES in 3 days and lead to the creation of 3DES and DES was later replaced by Rijndael algorithm as the Advanced Encryption Standard (AES) by NIST. 

How does DES work?

DES is a symmetric block encryption algorithm. This means that when 64-bit blocks of plaintext go in, 64-bit blocks of ciphertext comes out. Since it’s symmetric, the same key is used for encryption and decryption. When DES algorithm is applied to data, it divides the message into blocks and operates on them one at a time. The blocks are then put into 16 rounds of transposition and substitution functions.

What does it mean to be “broken”?

Algorithms are considered to be broken if someone uncovers a key that is used during an encryption process. You can break an algorithm by brute force attack of by identifying weaknesses in the algorithm itself.