NSA Codebreaker 2025 - Task 5: Putting It All Together

Sat, 03 Oct 2026 00:05:00 +0100

Task 5 - Putting It All Together - (Cryptanalysis)

NSA analysts confirm that there is solid evidence that this binary was at least part of what had been installed on the military development network. Unfortunately, we do not yet have enough information to update NSA senior leadership on this threat. We need to move forward with this investigation!

The team is stumped - they need to identify something about who was controlling this malware. They look to you. “Do you have any ideas?”

Crypto Cheatsheet for CTFs

Wed, 27 Aug 2025 00:00:00 +0000

Cryptography challenges are one of the most common categories in Capture the Flag (CTF) competitions. This guide provides a focused overview of essential algorithms, how to recognize them, common weaknesses exploited in CTFs, and practical resources for practice.

Common CTF Crypto Patterns

Flags often follow formats like CTF{...}, which can help in known-plaintext scenarios.
Key reuse across ciphertexts can allow XOR analysis.
Small RSA exponents (e = 3) can lead to direct root extraction if the plaintext is small.
Small primes allow for easy factorization of RSA moduli.
Padding issues in AES frequently lead to oracle-style attacks.
Images encrypted with ECB will show visible repeated patterns.

Tools

CyberChef - versatile tool for conversions, encodings, and ciphers.
CacheSleuth MultiDecoder - automated format and cipher detection. Easily my favorite tool.
dCode - classical cipher solvers and crypto utilities.
RsaCtfTool - specialized RSA attack tool.

Core Algorithms

RSA

RSA is an asymmetric encryption algorithm based on modular arithmetic with large primes.