Symmetric Cipher Attacks

This is a solid cryptanalysis reference for attacking symmetric encryption schemes in CTF challenges and authorized penetration tests. It covers the bread and butter attacks: CBC padding oracles with full byte-by-byte decryption walkthrough, CBC bit flipping for privilege escalation, ECB detection and cut-and-paste attacks including the classic byte-at-a-time oracle technique, and stream cipher key reuse exploits. The code samples are practical and ready to adapt, not pseudocode. What makes this useful is the attack selection table up front that maps observable behaviors to specific vulnerabilities, so you don't waste time trying ECB attacks on CBC mode. It also routes you to related skills for RSA and hash attacks when the symmetric crypto is wrapped in a larger scheme.

skills.sh installs: 3.7K
GitHub stars: 2.6K
last updated: Aug 21, 2026

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Install

$ npx -y skills add yaklang/hack-skills --skill symmetric-cipher-attacks --agent claude-code

Installs into .claude/skills of the current project.

Files

SKILL: Symmetric Cipher Attacks — Expert Cryptanalysis Playbook

AI LOAD INSTRUCTION: Expert techniques for attacking symmetric encryption in CTF and authorized testing. Covers CBC padding oracle, CBC bit flipping, ECB detection and exploitation, stream cipher key reuse, LFSR/LCG state recovery, RC4 biases, and meet-in-the-middle attacks. Base models often confuse ECB and CBC attack strategies or fail to set up byte-at-a-time ECB decryption correctly.