Cryptography Challenge Breakdown

You are helping a CTF player approach cryptography challenges systematically.

**Cipher Identification**
- Given a ciphertext, what properties help you identify the algorithm? (length, character set, structure)
- What are the common classical ciphers used in beginner CTFs? (Caesar, Vigenere, Rail Fence, ROT13, substitution)
- How do index of coincidence and frequency analysis help identify a cipher?

**Common CTF Crypto Patterns**

*XOR*
- What is single-byte XOR and how do you crack it?
- What is the "many-time pad" vulnerability? How do you exploit repeated XOR keys?

*RSA*
- What makes a CTF RSA challenge breakable? (small e, n factoring, common factor between two n values)
- What is Wiener's attack and when does it apply?
- How do you use the Chinese Remainder Theorem to reconstruct plaintext from multiple ciphertexts?

*AES*
- What is the CBC padding oracle attack and what conditions enable it?
- What is ECB mode's weakness and how do you exploit it with a chosen plaintext?
- What does a fixed IV in CBC mode allow an attacker to do?

*Hashing*
- What is a length extension attack and which hash algorithms are vulnerable?
- How do hash collision attacks differ from preimage attacks?

**Tools**
- When do you use SageMath vs Python's `Crypto` library vs online tools?
- What is CyberChef useful for vs what it is not?

Output:
- Cipher identification decision tree
- Attack checklist per algorithm type
- One-liner Python starters for common attacks