Cryptography

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Cryptography is the science of using codes and ciphers to conceal information. Cryptology is the study of cryptography. Codes and ciphers are terms that are often used interchangeably, but they are distinctly different. A code replaces one piece of information for another entirely different piece of information where the meaning of both is known to both the sender and recipient. A common example of this may be using a phrase such as We have contact to mean We have found the thing we're looking for. A cipher, on the other hand, modified the information itself to obscure its meaning. A cipher also conceals information but does so by changing the original information (plain text) to cipher text (sometimes referred to as 'black text'). The Polybius Cipher, described below, is an early example of a substitution cipher.

A timeline of cryptography through the middle ages may be found on the House Blue Heron Cryptography website [1].

Porta's (photograph by Kevin Baun, sca Melchior zum grauen Wolf)

Transposition Ciphers

A transposition cipher moves elements of the plain text and reorders the message so that it is unreadable without knowing the pattern[2].

   This is a rail fence cipher
   T   I   A   E   C   E
    H S S R I F N E I H R
     I   A   L   C   P
   TIAECE HSSRIFNEIHR IALCP

Substitution Ciphers

Polybius Cipher

This grid cipher substitution cipher is attributed to the Cleoxenus and Democleitus but was improved by and so attributed to Polybius in The Histories [3]. The basic operation of the 5x5 grid is to find the row and collum of each letter to produce an index value. Each index will have exactly two numbers for its index so spacing is not relevant to the code itself.

   A  T  L  A  N  T  I  A 
   11 44 31 11 33 44 24 11
1 2 3 4 5
1 A B C D E
2 F G H I/J K
3 L M N O P
4 Q R S T U
5 V W X Y Z

References

  1. Baun, Kevin W. “Cryptography Timeline.” History of Cryptography, February 17, 2020. http://crypto.houseblueheron.com/timeline.php.
  2. Baun, Kevin W. “Transposition Ciphers.” History of Crypto. Accessed February 17, 2020. http://crypto.houseblueheron.com/transposition.php.
  3. Citation needed