Classical cryptoRuns locallyNo account
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}