Nihilist Cipher
37 106 62 36 67 47 86 26 104 53 62 77 27 55 57 66 55 36 54 27
Encode text into additive number groups
The Nihilist cipher maps every letter to its Polybius coordinate, then adds the additive keyword's coordinates on top — the key repeats across the message, aligned letter by letter. With keyword “ZEBRAS” and additive “RUSSIAN”, “Dynamite Winter Palace” becomes “37 106 62 36 …”. The sums can exceed 99, which is why groups are spaced rather than run together.
When to use this tool
Reach for the Nihilist cipher when a puzzle, CTF challenge, or history-of-cryptography lesson hides a message as space-separated numbers like “37 106 62 36 …” instead of letters or coordinate pairs. Used by 19th-century Russian revolutionaries, it layers a running additive key on top of a Polybius square, so it bridges the substitution ciphers here (Caesar, Vigenère, Polybius Square) and the keyed-square family (Playfair, Bifid, ADFGVX) with a number-addition twist no other tool here produces.
Privacy and limitations
Everything runs locally in your browser; nothing is sent anywhere. This is a classical cipher, not real encryption — given enough ciphertext the additive key is recoverable. The 5×5 square merges I and J into one cell, so both encode the same way and always decode back to I. Encoding is case-insensitive and drops spaces, digits, and punctuation, so decoding returns letters only and the original spacing, casing, and J/I distinction are not recovered. You need the exact square keyword and additive keyword that encoded the message; this tool does not guess or auto-solve them. Use the encode/decode toggle to switch directions, since the transform is not self-inverse.