What are the three major categories of cryptanalysis, and which sub-types does classical cryptanalysis include?

Classical cryptanalysis (mathematical + brute force), implementation attacks (side channels), and social engineering — classical is further divided into mathematical analysis and brute-force methods.

1. Classical Cryptanalysis:

• Mathematical Cryptanalysis:
  • Differential Cryptanalysis
  • Linear Cryptanalysis
  • Algebraic attacks
  • Historical statistical methods (Kasiski test, frequency analysis for Enigma, etc.)
• Brute-Force Attacks:
  • Exhaustive key search
  • Table lookup
  • Time-Memory Tradeoff (TMTO) / Meet-in-the-middle

2. Implementation Attacks:

• Side-Channel Attacks (power analysis, timing, EM emissions)
• Fault injection (deliberately causing errors to leak information)
• These exploit how the algorithm is implemented, not the algorithm itself

3. Social Engineering:

• Bribery, blackmail, coercion
• Phishing, pretexting
• Exploits the human, not the cryptosystem

Key insight: A cryptosystem is only as strong as its weakest component. Even with a perfect algorithm and flawless implementation, social engineering can compromise the key holder directly.

Go deeper:

• Cryptanalysis (Wikipedia) — the overview of all attack families.
• Differential cryptanalysis (Wikipedia) — a flagship mathematical attack on block ciphers.
• Social engineering (Wikipedia) — attacking the human, not the cipher.