Information Security
For this week's discussion, consider the following prompts:
A cipher can be created by using a keyword. For example, if we choose "statistic" as our keyword, our cipher would be determined as follows:
Method I. Write the word "statistic" without the repeated letters. Then complete the cipher with the unused alphabet characters.
Standard sequence: 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 Z
Cipher sequence: S T A I C B D E F G H J K L M N O P Q R U V W X Y Z
In this case, the message HELLO becomes ECJJM. Comparing the standard sequence to the cipher sequence, you find that the letters U through Z are the same in both sequences. The number of letters that remain the same will depend upon the choice of the keyword. This can be avoided by using Method II.
Method II. Using the same keyword "statistic," another cipher can be created by writing it without its repeated letters and then writing the remaining alphabetical characters beneath the letters: S T A I C B D E F G H J K L M N O P Q R U V W X Y Z.
The cipher will be created by reading the table vertically and matching the letters to the standard sequence.
Standard sequence: 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 Z
Cipher sequence: S B H N U Z T D J O V A E K P W I F L Q X C G M R Y
Our message HELLO becomes DUAAP. A comparison of the standard sequence with the cipher sequence reveals that none of the characters are the same. Using Method II does not guarantee that there will be no matches; however, it does provide a better scrambled cipher than Method I.
Method III. The use of the first two methods results in one cipher for each keyword that is chosen. This type of code becomes relatively easy to break once the keyword is discovered. The use of a keyword and a setting word will generate multiple ciphers depending upon the number of characters in the setting word. For example, keeping our keyword as "statistic" and using "mode" as our setting word, the ciphers can be created as follows:
Using Method I, create the cipher:
Standard sequence: 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 Z
Cipher sequence: S T A I C B D E F G H J K L M N O P Q R U V W X Y Z
Using the letters of the setting word as the first character of the ciphers, four additional ciphers can be created.
Cipher 1: M N O P Q R U V W X Y Z S T A I C B D E F G H J K L
Cipher 2: O P Q R U V W X Y Z S T A I C B D E F G H J K L M N
Cipher 3: D E F G H J K L M N O P Q R U V W X Y Z S T A I C B
Cipher 4: E F G H J K L M N O P Q R U V W X Y Z S T A I C B D
Message: HELLO
Cipher 1: VQZZA
Cipher 2: XUTTC
Cipher 3: LHPPU
Cipher 4: MJQQV
Therefore, a message could be encoded using any one of the ciphers or a combination of the ciphers to make decoding by anyone but the intended receiver more difficult.
Based on working through each of these methods, discuss why the need for communication security protocols is significant. First, decode each of the ciphers. Second, discuss how communication security measures are built upon these principles. Third, discuss which existing communication security protocol you believe bears the greatest significance with regard to the level of protection that is offered. Finally, in responding to your peers' posts, discuss whether or not you believe there are any communication security protocols that were not mentioned but are of a greater significance.