Tool
Caesar Cipher
Shift plaintext letters by a fixed number of positions.
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Classical Ciphers
Explore historic hand ciphers, substitution systems, polyalphabetic methods, and coordinate-based designs with interactive tools and detailed guides.
Tools
Tool
Enigma Machine Simulator
Configure Enigma I, M3, or M4 rotors, ring settings, reflectors, and plugboard wiring with live output and signal tracing.
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One-Time Pad / Vernam Cipher
Encrypt or decrypt letters with an equal-length key, securely generate a random pad in your browser, and inspect every modulo-26 step.
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Vigenère Cipher
Polyalphabetic substitution cipher using a repeating key.
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Beaufort Cipher
Use a repeating keyword with the reciprocal Beaufort rule C = K - P mod 26.
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Autokey Cipher
Extend a keyword with plaintext letters for a stronger polyalphabetic stream.
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Polybius Square Cipher
Encode letters as row-and-column coordinates using the classic 5x5 Polybius square.
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Affine Cipher
Encrypt text with E(x) = (ax + b) mod 26 using configurable keys and formatting options.
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Hill Cipher
Encrypt letter blocks with square key matrices and modular arithmetic.
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Playfair Cipher
Encrypt letter pairs with a 5×5 keyword square and digraph rules.
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Keyword Cipher
Build a keyed substitution alphabet from a cleaned keyword.
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Pigpen Cipher
Turn letters into the geometric grid-and-X symbols of the Pigpen cipher, or decode a message with the clickable visual alphabet.
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Substitution Cipher
Encrypt or decrypt text with a fully custom monoalphabetic substitution alphabet.
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Bifid Cipher
Mix Polybius square coordinates in fixed-size blocks to create a fractionating classical cipher.
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Nihilist Cipher
Encrypt or decrypt numeric Nihilist ciphertext with a keyed Polybius square and repeated additive key.
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ADFGX Cipher
Use a keyed ADFGX square followed by keyed columnar transposition.
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ADFGVX Cipher
Use a keyed ADFGVX square with letters and digits, then apply keyed columnar transposition.
Open toolArticles
Caesar Cipher: A Secret in Plain Sight
Why the world's easiest cipher to break is still the perfect place to start learning.
Atbash Cipher: The Alphabet in a Mirror
How one of the oldest substitution ciphers turns A into Z, B into Y, and the alphabet into its own reflection.
Affine Cipher: Where Substitution Becomes Algebra
How multiplication, modular arithmetic, and a two-number key turned simple alphabet substitution into one of classical cryptography's cleanest mathematical teaching tools.
Keyword Cipher: When a Word Becomes a Secret Alphabet
How a memorable keyword builds a keyed substitution alphabet, and why the pattern still gives the game away.
Simple Substitution Cipher: Every Letter Wears a Mask
How a scrambled alphabet became the simplest general form of classical substitution, and why the patterns of language still give it away.
Pigpen Cipher: The Alphabet Hidden Inside a Grid
How corners, wedges, and dots turned ordinary letters into one of history’s most recognisable secret alphabets.
One-Time Pad: The Cipher That Cannot Be Broken
How a random key as long as the message turned simple addition into cryptography’s rarest promise—perfect secrecy—and why one reused page can bring the whole system crashing down.
Hill Cipher: The Day Classical Cryptography Became Mathematical
How Lester S. Hill's 1929 matrix cipher moved secret writing beyond alphabet tricks and toward the logic of modern cryptography.
Playfair Cipher: When Letters Started Moving in Pairs
How a 5×5 keyword square turned simple substitution into one of classical cryptography's most elegant hand ciphers.
Polybius Square Cipher: Turning Letters into Coordinates
How a 5×5 grid turned the alphabet into numbers, signals, and one of classical cryptography's most useful building blocks.
Tap Code Cipher: When Letters Became Knocks
How a 5×5 square turned the alphabet into row-and-column tap groups, and made communication possible through walls, pipes, floors, and silence.
Bifid Cipher: When Coordinates Get Split Apart
How the Polybius square became a fractionating cipher that mixed letters before turning them back into text.
Nihilist Cipher: Polybius Squares, Repeated Keys, and Number Codes
How a simple 5×5 letter square became a numerical cipher with two keys, repeated addition, and a revolutionary history.
Vigenère Cipher: When Classical Cryptography Learned to Change Alphabets
How a repeating keyword lets classical cryptography rotate among several alphabets instead of relying on one fixed substitution.
Beaufort Cipher: Vigenère in the Mirror
How a reversed keyword rule made one of classical cryptography's neatest self-undoing ciphers.
Autokey Cipher: When the Message Becomes the Key
How a Vigenère-style cipher tried to escape repetition by feeding the plaintext back into the keystream.
Enigma Machine: The Cipher That Changed with Every Keypress
How rotating wired wheels, a reflector, and a plugboard created one of history’s most formidable cipher machines—and how mathematics, engineering, captured documents, and human mistakes brought it down.
How to Use the Enigma Machine Simulator: Complete Guide
A complete practical walkthrough of the CipherRegister Enigma simulator, from the first test vector to M4 keys, signal tracing, custom rotors, troubleshooting, and deciphering.
ADFGX and ADFGVX: Fracturing Letters for Wartime Radio
The World War I field ciphers that split characters into coordinates, scattered those coordinates across the page, and made intercepted radio traffic far harder to analyse at speed.