Symmetric

The Polyalphabetic Cipher is a class of substitution ciphers that uses multiple cipher alphabets instead of a single one. Unlike a simple substitution cipher where each plaintext letter always maps to the same ciphertext letter, a polyalphabetic system changes the substitution depending on position in the message. This shifting pattern helps obscure letter frequencies, making the cipher far more resistant to classical frequency analysis.

The Pinprick Cipher is a simple symbolic substitution cipher in which letters are represented by patterns of dots (·) and circles (o). It works by assigning a unique sequence of these symbols to each letter, making it easy to encode short messages while hiding them in plain sight. Its origin is somewhat obscure, but it was historically used for secretive or playful communications, often in correspondence or small notes.

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.

The Ottendorf Cipher is a historical book-based substitution cipher where each character of the plaintext is represented by a triplet indicating the page, line, and word in a pre-agreed source text. The sender and recipient must share the same book (or document) and numbering method. This method hides the message in plain sight by encoding it as seemingly mundane numbers, making it ideal for espionage and covert communication.

The Null Cipher is a steganographic technique that hides a secret message within an ordinary-looking text. Most letters in the text are "nulls" and do not convey information, while only certain letters—determined by a prearranged rule—carry the hidden message. Its security relies on subtlety: without knowledge of the extraction rule, the cover text appears completely normal.

The Map Cipher is a simple substitution cipher that encodes messages using a geographic or visual reference, often overlaying a plaintext message onto a map and extracting letters based on pre-defined coordinates or zones. Each plaintext letter is mapped to a position on the map, and the corresponding symbol, letter, or code from that location becomes the ciphertext. This type of cipher combines geographic knowledge with substitution to obscure the message.

The Keyboard Code is a playful substitution cipher that maps letters to other keys based on their positions on a standard QWERTY keyboard. Instead of using numerical shifts like the Caesar Cipher or keyword sequences like the Kangaroo Cipher, this cipher substitutes each letter according to a physical adjacency or pattern on the keyboard layout.

The Homophonic Substitution Cipher is a sophisticated variant of substitution ciphers in which a single plaintext letter can map to multiple possible ciphertext symbols. This reduces the risk of frequency analysis since high-frequency letters do not always produce the same ciphertext character. Unlike simple systems such as the Simple Substitution Cipher, the homophonic approach creates a more uniform statistical distribution of symbols in the ciphertext.

The Hill Cipher is a classical polygraphic substitution cipher invented by Harold Hill in 1929. Unlike simple substitution ciphers, which encode one letter at a time, the Hill Cipher operates on blocks of letters, using linear algebra and matrix multiplication over modular arithmetic. This allows it to encode multiple letters simultaneously, providing greater resistance to frequency analysis.

The Gronsfeld Cipher is a variant of the Caesar Cipher that uses a numeric key to perform multiple shifts on the plaintext. Named after the German banker Baron Gronsfeld in the 19th century, it operates like a Caesar shift but allows each letter to be shifted by a different amount based on the corresponding digit of the key.