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A transposition cipher that writes the message on alternate lines across the page, and then reads off each line in turn.

An early form of a cipher system using a set of cipher disks, each with the 26 letters of the alphabet arranged randomly around them, which can be rotated and aligned to create different substitution ciphers.

A polyalphabetic cipher invented by Leon Battista Alberti in which the cipher text alphabet rotates during encryption.

An asymmetric cipher developed in 1977 by Ron Rivest, Adi Shamir, and Leonard Adleman, where encryption and decryption use different keys.

A cipher that incorporates the message (the plaintext) into the key, making it more resistant to frequency analysis than the Vigenère cipher.

A transposition cipher where a sheet of paper with holes is placed over a plaintext message, allowing selective encoding of the text.

A geometric simple substitution cipher, which uses a series of symbols to replace the letters. It was used by the Freemasons to keep their records private.

A polyalphabetic substitution cipher invented by Giovanni Battista della Porta, where instead of using a keyword, two halves of the alphabet are used as the table to encipher the text.

A fractionating transposition cipher used by the German Army during World War I which combined a modified Polybius square with a single columnar transposition.

A polygraphic substitution cipher based on linear algebra, invented by Lester S. Hill in 1929. It uses matrix multiplication to mix up the plaintext.

A set of three cipher texts that supposedly pinpoint the location of buried treasure in gold, silver, and jewels estimated to be worth over USD 60 million.

A cipher that uses a book or other document as the key, where the words or letters in the book correspond to a coded message.

A method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword.

A digraph substitution cipher that encrypts pairs of letters (digraphs), making it harder to break than traditional single-letter substitution ciphers.

A mechanical wheel cipher device consisting of 25 aluminum disks containing letters A through Z used by the United States Army.

A type of monoalphabetic substitution cipher where each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter.

A cipher that uses four 5x5 squares to translate each letter pair of the plaintext into different letter pairs, or ciphertext, using a double substitution mechanism.

A mysterious cipher authored by the composer Edward Elgar in 1897, consisting of 87 characters, each made from a set of semi-circles oriented in one of eight possible directions.

A cipher machine used by the Japanese Foreign Office to encode diplomatic messages during World War II. It was solved by the American cryptographer William F. Friedman.

A substitution cipher originally used to encrypt the Hebrew alphabet where the first letter is replaced by the last letter, the second by the second-last, and so on.

A cipher that uses the characters of the Cherokee syllabary to encode messages, known for being used by the members of the Cherokee nation.

A German cipher machine used during World War II, which featured a set of wheels (rotors) to provide a polyalphabetic substitution cipher.

A substitution cipher where each letter in the plaintext is shifted a certain number of places down the alphabet.

A simple Caesar cipher with a shift of 13 places, used on the internet as a means of obscuring text (e.g., spoilers, puzzle solutions).

A secret communication issued from the German Foreign Office in January 1917 that proposed a military alliance between Germany and Mexico, if the United States entered World War I against Germany.

A steganographic method devised by Francis Bacon in which each letter of the plaintext is replaced by a group of five characters consisting of 'A' or 'B'.

An ancient transposition cipher used by the Spartans where a strip of parchment was wound around a rod of a certain diameter; the message was written across the rod and then unwound.

A British nickname for the Lorenz SZ cipher machine used by the Germans during World War II and eventually decrypted by Colossus, an early electronic computer.

A series of electro-mechanical rotor cipher machines used by the Germans during World War II.