Tuesday, December 2, 2008

Codes, Ciphers, Encryption and Cryptography

Cryptography is the discipline of using codes and ciphers to encrypt a message and make it unreadable unless the recipient knows the secret to decrypt it. Encryption has been used for many thousands of years. The following codes and ciphers can be learned and used to encrypt and decrypt messages by hand. Monoalphabetic Ciphers

A monoalphabetic cipher uses the same substitution across the entire message. For example, if you know that the letter A is enciphered as the letter K, this will hold true for the entire message. These types of messages can be cracked by using frequency analysis, educated guesses or trial and error.

* Caesar Cipher
* Atbash Cipher
* Keyword Cipher
* Pigpen / Masonic Cipher
* Polybius Square

Polyalphabetic Ciphers

In a polyalphabetic cipher, the substitution may change throughout the message. In other words, the letter A may be encoded as the letter K for part of the message, but later on it might be encoded as the letter W.

* Vigenère Cipher
* Beaufort Cipher
* Autokey Cipher
* Running Key Cipher

Polygraphic Ciphers

Instead of substituting one letter for another letter, a polygraphic cipher performs substitutions with two or more groups of letters. This has the advantage of masking the frequency distribution of letters, which makes frequency analysis attackes much more difficult.

* Playfair Cipher
* Bifid Cipher
* Trifid Cipher
* Four-square cipher

Transposition Ciphers

Unlike substitution ciphers that replace letters with other letters, a transposition cipher keeps the letters the same, but rearranges their order according to a specific algorithm.

* Rail Fence
* Route Cipher
* Columnar Transposition

Other Ciphers and Codes

* Book Cipher
* Beale Cipher
* Morse Code
* Tap Code
* One-time Pad
* Scytale
* Semaphore
* Steganography

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