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

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

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

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

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

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'.

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

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 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.

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

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

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.

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

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

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

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.