Classical Ciphers Tools

Free classical cipher encoders and decoders that run entirely in your browser — Caesar, Atbash, affine, rail-fence, columnar transposition, Bacon, Polybius, Playfair, A1Z26, keyword, Bifid and Beaufort, plus an automatic cipher identifier. Great for puzzles, CTFs and escape rooms. Nothing is uploaded.

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Caesar Cipher Encoder / Decoder

Encode or decode text with a variable-shift Caesar cipher, and brute-force all 26 shifts at once with an automatic best-guess to crack unknown keys.

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Atbash Cipher Encoder / Decoder

Substitute each letter with its mirror in the alphabet (A↔Z, B↔Y, …). This classic cipher is self-inverse, so one operation both encodes and decodes.

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Affine Cipher Encoder / Decoder

Monoalphabetic cipher using E(x)=(a·x+b) mod 26, with key validation (gcd(a,26)=1) and modular-inverse decoding. Encode or decode letters instantly.

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Rail Fence Cipher Encoder / Decoder

Zig-zag transposition cipher: write text diagonally across N rails then read it off row by row. Encode or decode with adjustable rails and starting offset.

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Columnar Transposition Cipher

Keyword-driven columnar transposition: fill a grid row-wise, then read columns in the alphabetical order of the keyword letters. Complete or incomplete variant.

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Baconian (Bacon) Cipher Encoder / Decoder

Encode each letter as a 5-symbol group of A's and B's (or 0/1) — the biliteral Bacon cipher. Supports the 24-letter classic and 26-letter distinct tables.

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Polybius Square Cipher Encoder / Decoder

Convert letters to two-digit row/column coordinates on a 5×5 Polybius square (basis of the tap code). Keyword-seeded squares and I/J or C/K merge supported.

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Playfair Cipher Encoder / Decoder

Encode or decode text with the classic Playfair digraph cipher using a 5x5 keyword square, with automatic X-padding and the key square shown.

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A1Z26 Letter-Number Cipher (Encoder / Decoder)

Convert letters to their alphabet positions (A=1 … Z=26) and back, with a choice of separators and optional 0-based indexing — the Gravity Falls cipher.

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Keyword (Monoalphabetic Substitution) Cipher

Build a substitution alphabet from a keyword and encode or decode text through it, with the full plain-to-cipher mapping table displayed.

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Bifid Cipher Encoder / Decoder

Encrypt or decrypt text with Delastelle's Bifid cipher, a fractionating Polybius-square cipher with a configurable keyword and period; key square shown.

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Beaufort Cipher Encoder / Decoder

Encrypt or decrypt with the reciprocal Beaufort cipher C = (K − P) mod 26, a self-inverse polyalphabetic cipher, with an optional German-variant mode.

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Cipher Identifier / Analyzer

Analyze unknown ciphertext by its statistical fingerprint — index of coincidence, chi-square, character set — and rank the most likely classical ciphers.

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