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# Classical Ciphers

Straddle Checkerboard Cipher is a substitution cipher, except that the substitutions are of variable length. It has formed a component of several impotant field ciphers, the most notable being the VIC cipher used by russian spies during the cold war.

#### Running Key Cipher

Running Key Cipher is a type of polyalphabetic substitution cipher in which a text, typically from a book, is used to provide a very long keystream.

#### Simple Substitution Cipher

Simple Substitution Cipher is a cipher that has been in use for many hundreds of years. It basically consists of substituting every plaintext character for a different ciphertext character.

#### ROT13 Cipher

ROT13 Cipher is a simple letter substitution cipher with a specific key where the letters of the alphabet are offset 13 places.

#### Porta Cipher

Porta Cipher is a polyalphabetic substitution cipher invented by Giovanni Battista della Porta. Where the Vigenere cipher is a polyalphabetic cipher with 26 alphabets, the Porta is basically the same except it only uses 13 alphabets. The 13 cipher alphabets it uses are reciprocal, so enciphering is the same as deciphering.

#### Columnar Transposition Cipher

Columnar Transposition Cipher is a fairly simple, easy to implement cipher. It is a transposition cipher that follows a simple rule for mixing up the characters in the plaintext to form the ciphertext.

#### XOR Cipher

XOR Cipher is a type of additive cipher.

#### Vernam Cipher

Vernam Cipher (also known as the one-time pad (OTP)) is an encryption technique that cannot be cracked, but requires the use of a one-time pre-shared key the same size as, or longer than, the message being sent.

#### Four-Square Cipher

Four-Square Cipher encrypts pairs of letters (like playfair), which makes it significantly stronger than substitution ciphers etc. since frequency analysis becomes much more difficult.

#### Bifid Cipher

Bifid Cipher is a cipher which combines the Polybius square with transposition, and uses fractionation to achieve diffusion.