Symmetric

The Polyalphabetic cipher is a classical encryption method that uses multiple substitution alphabets to encode plaintext, significantly increasing security compared to monoalphabetic ciphers. It was first formalized by the Italian cryptographer Giovan Battista Bellaso in 1553 and later popularized by Vigenère in 1586 through what is now called the Vigenère cipher. In a polyalphabetic system, a keyword determines which substitution alphabet is applied to each plaintext letter.

The Pinprick Cipher is a basic and straightforward form of secret writing, often used for encoding messages in a discreet manner. It involves using a pin or a sharp tool to create small holes or dots on a piece of paper in a specific pattern to represent letters, numbers, or symbols.

To use the Pinprick Cipher, each letter, digit, or symbol in the plaintext is assigned a unique pattern of holes or dots. The pattern could be based on a predefined code, a secret key, or any agreed-upon method between the sender and recipient.

The Pigpen Cipher, also known as the Masonic Cipher or Freemason's Cipher, is a simple substitution cipher used for encoding secret messages. It has its roots in the ancient practice of symbolic writing and is often associated with Freemasonry, a fraternal organization known for its use of secret symbols and rituals.

Ottendorf Cipher is a classical book cipher technique that encodes a secret message by referencing the positions of words or letters within a pre-agreed text, typically a book, newspaper, or any shared document. Each element of the ciphertext specifies a page, line, and word (or sometimes letter), allowing the recipient to reconstruct the message by locating the indicated elements. The strength of the Ottendorf Cipher relies entirely on the secrecy of the chosen text and the agreed-upon indexing scheme.

Keyboard Code, also known as Keyboard Cipher or Keyboard Encryption, is a simple and straightforward method of encrypting and decrypting messages using a keyboard layout as a reference. It is a type of substitution cipher, where each letter of the plaintext is replaced with a corresponding letter from the keyboard layout.

The Homophonic Substitution cipher is a classical substitution cipher designed to replace each plaintext character with one of several possible ciphertext symbols, reducing the effectiveness of frequency analysis. While its exact origins are unclear, it became widely studied in the 16th and 17th centuries and was employed in diplomatic and military communications to obscure letter frequencies. In this cipher, high-frequency letters like E or T are assigned multiple ciphertext equivalents, while less frequent letters may have only one.

The Hill cipher is a polygraphic substitution cipher invented by the American mathematician Lester S. Hill in 1929. Unlike simple substitution ciphers, the Hill cipher encrypts blocks of letters using linear algebra, making it one of the first ciphers to apply matrix operations to cryptography. Each block of plaintext letters is represented as a vector of numbers (with A=0, B=1, …, Z=25) and multiplied by an invertible key matrix modulo 26.

The Gronsfeld Cipher is a variation of the Vigenère cipher, attributed to the German mathematician Johann Gronsfeld, who introduced it in 1863. It was primarily developed as a method for encrypting messages using a numeric key, making it a simpler form of the more complex Vigenère cipher.