DES
What is DES (Data Encryption Standard)?
DES is a symmetric block cipher algorithm that was the federal standard for encryption from 1977 to 2002. It processes data in 64-bit blocks using a 56-bit key (technically 64 bits with 8 parity bits). The algorithm uses multiple rounds of substitution and permutation operations to create complex encryption.
Key Components:
1. 64-bit input block
2. 56-bit key (effective)
3. 16 rounds of processing
4. Initial and final permutations
5. S-boxes (substitution boxes)
6. P-boxes (permutation boxes)
Key Process Steps:
1. Initial Permutation (IP)
2. 16 Rounds of:
• Key scheduling
• Expansion permutation
• XOR with subkey
• S-box substitution
• P-box permutation
3. Final Permutation (IP⁻¹)
Strengths (Historical):
• Well-analyzed security
• Fast hardware implementation
• Simple design principles
• Good avalanche effect
Weaknesses:
• Key too short (56 bits)
• Vulnerable to brute force
• S-boxes design not explained
• Slow in software
Modern Variants:
• 3DES (Triple DES)
• DESX
• DES-X
• G-DES