Cryptography Checklist

Initial Assessment:

• Identify the type of cryptography used (symmetric, asymmetric, hashing, etc.).

• Look for any hints that might indicate a specific cipher or algorithm.

Common Ciphers and Encodings:

• Check for basic encoding schemes (Base64, Hex, ASCII, etc.).

• Test for simple ciphers (Caesar, ROT13, Vigenère, etc.).

• Use online tools or scripts to quickly test these possibilities.

Symmetric Key Cryptography:

• If a key is provided or can be guessed, try decrypting with common algorithms (AES, DES, etc.).

• Check for weak keys or implementation flaws.

Asymmetric Key Cryptography:

• Analyze any provided keys or ciphertexts.

• Check for weak keys, small key sizes, or common vulnerabilities like small prime numbers in RSA.

Cryptographic Protocols:

• Understand the cryptographic protocol or scheme being used (if any).

• Look for protocol-specific vulnerabilities or misconfigurations.

Hash Functions:

• Identify the hash function used.

• Attempt to crack hashes using rainbow tables or brute force, if feasible.

• Look for vulnerabilities like hash collisions.

Cryptanalysis Techniques:

• Apply classical cryptanalysis techniques (frequency analysis, known plaintext, etc.).

• Look for patterns or statistical anomalies in ciphertext.

Modern Cryptography Attacks:

• Consider side-channel attacks, padding oracle attacks, etc., if the scenario suggests their applicability.

• Research any recent vulnerabilities in cryptographic algorithms or implementations.

Scripting and Automation:

• Write or use existing scripts to automate decryption or analysis tasks.

• Use tools like Python with libraries (e.g., pycrypto, hashlib) for custom cryptanalysis.

Challenge Context:

• Consider the context of the challenge for any thematic hints or clues.

• Sometimes the key or a hint to the solution is hidden in the challenge description or storyline.

Validation of Findings:

• Test your findings against the challenge.

• It's common in CTFs for the output to be a flag in a specific format (e.g., flag{...}).

Research and Learning:

• If stuck, research cryptographic methods and past CTF write-ups for ideas.

• Cryptography challenges often require learning new concepts and techniques.

Documentation:

• Keep notes on your process and solutions.

• Documenting your approach can be invaluable for learning and for future challenges.