picoCTF Solutions

Tools / Cipher Identifier

Cipher Identifier & Auto-Decoder

Paste a string and this tool tries every common decoder (base64, hex, Morse, ROT/Caesar, Atbash, Bacon, binary, decimal codepoints, URL-encoded), scores each result by how English it looks, and shows the top hits. Inspired by CyberChef’s Magic recipe but focused on the encodings that show up in CTF challenges.

Decoder candidates (sorted by English-likeness)

Paste ciphertext above. The tool tries every common decoder and ranks the results.

How the ranking works

Each candidate is scored on (1) how closely its letter frequency matches English (chi-square fit), (2) how many common English words appear, and (3) whether it contains a flag-shaped string like picoCTF{...}. High-confidence hits glow green; weaker guesses are shown for completeness so you can spot patterns the scorer missed (numeric flags, leetspeak, language other than English).

For chained encodings (base64 wrapping hex wrapping ROT13, etc.) the tool tries up to two passes automatically. If nothing scores above the threshold, the input is likely keyed (Vigenere, RSA, AES) - open the Vigenere, RSA Calculator, or AES Decryptor and supply the key. Substitution ciphers are best attacked with the Frequency Analysis tool.

Challenges that use this tool