Numeric

The Nomenclator Cipher is a classical encryption system that combines a substitution cipher with a codebook. Unlike standard substitution ciphers that operate purely on individual letters, the Nomenclator Cipher allows entire words, names, or phrases to be replaced with predefined numeric or symbolic codes. This hybrid approach significantly enhances security by masking both letter frequencies and common word patterns.

The Nihilist Substitution Cipher is a classical encryption method that combines a Polybius square with a numeric additive key to produce a numeric ciphertext. It was historically used for its simplicity in encoding messages into numbers while maintaining a level of secrecy. Each letter of the plaintext is converted into a two-digit number via a Polybius square and then offset by a numeric key to generate the final ciphertext.

The Checkerboard Cipher, also known as the Polybius Checkerboard Cipher, is a classical substitution cipher that converts letters into numeric pairs or digits using a keyword-based grid. Each letter is assigned a coordinate in a 5x5 or 6x5 checkerboard matrix, with the keyword determining the arrangement of letters. This approach allows letters to be represented as one or two digits, providing a compact numeric encoding while introducing a keyed substitution system.

The Cadenus Cipher is a polyalphabetic substitution cipher that uses a repeating keyword to alter the shift of each plaintext character. Named in reference to classical ciphering techniques, it is similar in principle to the Vigenère Cipher, but often employs a direct letter-to-letter mapping that adapts dynamically according to the keyword.

The VIC Cipher is a complex hand cipher developed during the Cold War and used by Soviet intelligence operatives. Unlike simpler substitution or transposition ciphers, the VIC Cipher combines multiple cryptographic techniques into a layered system, including a Polybius-style checkerboard, modular arithmetic, and columnar transposition. This hybrid approach produces numeric ciphertext that is highly resistant to classical cryptanalysis when executed correctly.

The Nihilist Cipher is a polygraphic substitution cipher that combines the principles of the Polybius Square with a numeric key to produce a series of ciphertext numbers. It was developed in the 19th century by Russian nihilists to securely transmit messages, hence its name. Each letter is first converted into a pair of digits using a Polybius grid, then combined with corresponding digits from a numeric key by addition, resulting in ciphertext that appears as a sequence of numbers.

The Knapsack Cipher is a public-key cryptosystem based on the mathematical problem of the subset sum, also known as the "knapsack problem." It was one of the first attempts at a public-key encryption scheme, proposed by Ralph Merkle and Martin Hellman in 1978. The cipher transforms a plaintext message into a binary representation and encodes it as a sum of elements from a specially chosen sequence, making decryption without the private key computationally difficult.

The Route Cipher is a columnar transposition cipher that rearranges letters of a plaintext into a grid defined by a keyword. Letters are then read off column by column in alphabetical order of the keyword letters. Spaces are removed during encoding, and if the last row is incomplete, it may be padded to fill the grid. The recipient decodes by reconstructing the grid and reading row by row.

Its security relies entirely on the secrecy of the keyword. It does not substitute letters but only rearranges them.

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 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.