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crypto-analysis

@kiwamizamurai/cctf
1
24

Breaks cryptographic systems and decrypts ciphertext. Use when working with RSA, AES, XOR, classical ciphers, hash functions, or when challenge involves encryption, decryption, keys, or mathematical crypto attacks.

Install Skill

Shared

Installs to .agents/skills, used by Codex, Amp, Warp, Cursor, OpenCode, and more.

CodexAmp
WarpCursorOpenCode
ClineGemini CLI
GitHub Copilot
Personal

Available across projects.

$npx skills-installer add @kiwamizamurai/cctf/crypto-analysis --client shared
Project

Writes to .agents/skills.

$npx skills-installer add @kiwamizamurai/cctf/crypto-analysis -p --client shared
Note: Review the skill instructions before using it.

SKILL.md

name crypto-analysis
description Breaks cryptographic systems and decrypts ciphertext. Use when working with RSA, AES, XOR, classical ciphers, hash functions, or when challenge involves encryption, decryption, keys, or mathematical crypto attacks.
allowed-tools Bash, Read, Write, Grep, Glob

Crypto Analysis Skill

Quick Workflow

Progress:
- [ ] Try Ciphey auto-decrypt first
- [ ] Identify crypto type (RSA/AES/XOR/classical)
- [ ] Check for known weaknesses
- [ ] Implement attack
- [ ] Decrypt flag

Step 1: Auto-Decrypt (Try First!)

ciphey -t "ENCODED_TEXT"    # Auto-detects and decrypts
ciphey -f encrypted.txt     # From file

Step 2: Identify Crypto Type

Pattern Crypto Type Reference
n, e, c variables RSA reference/rsa-attacks.md
16/32 byte key, IV AES reference/aes-attacks.md
XOR operations XOR/Stream reference/classical.md
Polynomial mod Lattice reference/lattice.md

RSA Attack Decision Tree

├── e small (≤5)?     → Direct eth root
├── e very large?     → Wiener's Attack
├── Multiple n,e,c?   → Hastad's Broadcast
├── Same n, diff e?   → Common Modulus
├── GCD(n1,n2) > 1?   → Common Factor
├── p ≈ q?            → Fermat Factorization
├── dp/dq leaked?     → Partial Key Recovery
└── Default           → FactorDB / yafu

Full implementations: reference/rsa-attacks.md

Quick Commands

# Auto-decrypt
ciphey -t "text"

# XOR analysis
xortool encrypted.bin
xortool -c 20 encrypted.bin  # Expect spaces

# Factor large n
yafu "factor(<n>)"

# RSA tool
python3 RsaCtfTool.py -n <n> -e <e> --uncipher <c>

# Lattice (SageMath)
sage solve.sage

Reference Files

  • RSA Attacks: Small e, Wiener, Hastad, Common Modulus, Fermat, FactorDB
  • AES Attacks: ECB detection, CBC flip, Padding Oracle
  • Classical/XOR: Ciphey, xortool, frequency analysis, Vigenère
  • Lattice: Coppersmith, LLL, HNP