Ciphers
Cipher challenges are among the most common in CTFs. They involve text encrypted with classical algorithms such as substitution, transposition, and polyalphabetic ciphers, or sometimes modern block‑cipher puzzles.
Your goal is to recognize the cipher type, then decode or break it.
Clues can come from:
- Character distribution (frequency analysis)
- Alphabet size (26, digits only, alphanumeric)
- Repeating patterns or shifts
- Presence of markers like
{,_, or==(Base64)
| Cipher | Type / Family |
|---|---|
| Caesar / ROT13 | Shift (Substitution) |
| Atbash | Substitution |
| Vigenère | Polyalphabetic (Keyword) |
| Affine | Mathematical (Substitution) |
| Substitution / Monoalphabetic | 1‑to‑1 mapping |
| Rail Fence | Transposition |
| Columnar Transpose | Transposition |
| Playfair | Polyalphabetic digraph |
| Hill Cipher | Matrix‑based |
| Baconian | Steganographic cipher |
| Morse Code | Binary encoding |
| Base32/64/58/85 | Encoding, not cipher |
| XOR Cipher (single‑byte) | Modern toy cipher |
| Enigma / Rotor | Mechanical cipher |
- Observe the format
- Length, character set, repeating letters, presence of symbols
- Check for common encodings
- Ends with
==: Base64 - Only hex digits: Hex / Base16
- Ends with
- Apply automatic tools
- Frequency Analysis
- Compare common letters to English distribution (
etaoinshrdlu)
- Compare common letters to English distribution (
- Try simple shifts
- ROT13 / ROT47 / Caesar
- Layered Encodings
- Many CTFs stack multiple layers (e.g., Base64 > Vigenère > ROT13)
- Check for word patterns
_or{may mark flag fragments even in ciphertext.
| Tool | Purpose |
|---|---|
| dCode.fr Cipher Identifier | Detect and solve classical ciphers |
| Boxentriq Cipher Identifier | Online pattern recognizer + auto‑solver |
| quipqiup | Monoalphabetic substitution solver |
| CrypTool Online | Comprehensive crypto suite for education |
| CyberChef | Universal decoder pipeline for layered encodings |