Atbash cipher decoder
Decode Atbash, the keyless substitution that maps A to Z, B to Y, and so on. Its own inverse.
Open in ctfpalAtbash mirrors the alphabet: A becomes Z, B becomes Y, M becomes N. There is no key, so there is nothing to break - only to recognise. Applying it twice returns the original.
Recognising it
Atbash preserves letter frequencies in mirrored form, which produces a distinctive signature: the ciphertext is unusually rich in Z, V, and S (the images of A, E, and H) and unusually poor in E. A frequency chart with a tall bar at the far right end rather than the middle is the visual tell.
Formally, Atbash is the affine cipher with a = 25 and b = 25, so an affine brute force finds it too - but as a named single click it costs nothing to rule out early.
Worked example
Atbash
Input
krxlXGU{zgyzhs_rh_prmw_lu_zuurmv}Result
picoCTF{atbash_is_kind_of_affine}Go deeper
- Chi-squared, index of coincidence, and why classical ciphers fallCaesar, Vigenere, and substitution ciphers do not need guesswork - they need two statistics. How chi-squared scores a candidate plaintext, how the index of coincidence recovers a key length, and how to combine them into an attack that runs in milliseconds.
Related tools
Caesar cipher decoder with automatic shift detection
Break a Caesar shift without guessing. ctfpal scores all 26 rotations by chi-squared letter frequency and puts the English one first.
Affine cipher solver
Brute-force every valid affine key pair and rank the 312 candidate decryptions by English-likeness.
Cipher identifier and automatic decoder
Paste anything and find out what it is. ctfpal runs every decoder and rotation, including multi-pass cascades, and ranks results by English-likeness and flag patterns.
ROT13 decoder
Apply ROT13 (and ROT47) instantly. ROT13 is its own inverse, so the same operation encodes and decodes.