SECURING FIBRE CHANNEL FABRICS - Brocade

Chapter 5: Elementary CryptographyFor example, if the Latin/Roman alphabet is shifted by five letters, thefollowing cipher results.Original alphabet: A B C D E F G H I J K L M N O P Q R S T U V W X Y ZCipher code: F G H I J K L M N O P Q R S T U V W X Y Z A B C D EUsing this cipher, the word “RETREAT” would be encoded as “WJY-WJFY.” This type of cipher is also known as a transposition cipher. Asubstitution cipher is another type of cipher, which mixes up the lettersin no particular order.For example, if the order of the Latin/Roman alphabet is randomized,the following cipher results.Original alphabet: A B C D E F G H I J K L M N O P Q R S T U V W X Y ZCipher code: Q F B O R X K U G W I P A N S Z H T D J C Y M E L VUsing this cipher, the word “RETREAT” would be encoded as“TRJTRQJ.” Although these basic ciphers can probably be decodedeasily by most weekend puzzle enthusiasts, they were neverthelessuseful in their time.Mechanical devices have been developed to refine the encoding anddecoding of messages. One of the best known encoding devices is theGerman Enigma Machine used in World War II, which used multiplepasses of a simple alphabet substitution cipher. The electronic ageintroduced computers and electronic devices, which further increasethe complexity and speed of the encoding process and subsequentlythe difficulty of decoding messages without the key.For as long as cryptography has been around, there has also been anequivalent aspiration to decode messages. The process of decipheringmessages without access to the key is called cryptanalysis.74 Securing Fibre Channel Fabrics