Assignment: Townsville & Cairns
Aim: This assignment is designed to help you improve your critical thinking and problem solving skills, as well as your information literacy skills (i.e. the ability to select and organise information and to communicate it effectively and ethically).
Requirements, Method of Submission, and Marking Criteria:
• Answer all of the following questions in a single document. Each question should begin on a new page.
• For each of the first two (2) questions, write a report of approximately 1000 words in the structure of a scientific paper.
• Include your name on the first page. Include list of references for each question with proper in-text citations.
• For marking criteria of the first 2 questions, see the included rubric.
• In your answer to question 3 (i.e., cryptanalysis), show all your work. Four (4) marks are assigned to the determination of the correct key-length, four marks to the determination of correct keyword and two marks for determination of the complete plaintext (partial marks count).
• Upload your solution to the Assignment Box, located in the subject's site.
1. Bring Your Own Device (BYOD) Policy
Use the Internet to locate BYOD Policy from two different organizations. After reading that information, create your own BYOD policy for your school or place of employment. What restrictions should be enforced? What control should the organization have over the personal devices?
Write a short (approximately 1000 words) report on your research.
2. Open Authentication (OAuth)
Use the Internet to research OAuth. What is the technology behind it? What are its strength? What are its weaknesses? Will it replace OpenID? Would you recommend it for secure applications like online banking?
Write a short (approximately 1000 words) report on your research.
3. Cryptanalysis of Polyalphabetic Ciphers:
In this question you learn a classical polyalphabetic substitution cipher (known as Vigen´ere cipher), and are required to cryptanalysis a given cryptogram. Cryptanalysis of an information system is the study of mathematical techniques for attempting to defeat information security services. A cryptographic system is said to be breakable if a third party (i.e., cryptanalyst), without prior knowledge of the key, can systematically recover plaintext from corresponding ciphertext within an appropriate time frame.
Background
Julius Caesar used a cipher which moved each letter of the alphabet to the letter three to the left in the predetermined order of the letters of the alphabet. Figure 1 shows original English alphabet and corresponding cryptogram alphabet in Caesar cipher:
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 d e f g h i j k l m n o p q r s t u v w x y z a b c
Figure 1: English alphabet letter and their corresponding cryptograms in the Caesar cipher
In order to use mathematical notations, let convert letters of the alphabet to integers. The most natural conversion is to assign to each letter an integer which indicates the position of the letter in the alphabet. That is, assign 0, 1, ... , 24, 25 to a, b, • • • , y, z, respectively. Using this conversion, Caesar cipher can be expressed as:
C = Ek(M ) = M + 3 (mod 26)
where ‘C' is the cryptogram, ‘E' is the encryption algorithm, ‘k' is the key, ‘M' is the message/plaintext (one may replace integer 3 by letter ‘d').
Caesar cipher is from the family of shift ciphers, in which the cryptogram is a shifted version of the original alphabet. Cryptanalysis of the Caesar (and all shift ciphers) is easy, because there are 26 possible keys/shift.
Vigen´ere Cipher
In Vigen´ere cipher the key is more than one letter. That is, Vigen´ere cipher can be considered as a combination of n shift ciphers, where n is the key-length (i.e., the number of letters in the keyword). Let the message/plaintext be ‘individual character' and the keyword is ‘host'. Vigen´ere cipher encrypts the message as follows:
Plaintext i n d i v i d u a l c h a r a c t e r
Keyword h o s t h o s t h o s t h o s t h o s
Cryptogram p b v b c w v n h z u a h f s v a s j
That is, the first four letters of cryptogram computed as:
‘i' + ‘h' = 8 + 7 = 15 (mod 26) i.e., p
‘n' + ‘o' = 13 + 14 = 1 (mod 26) i.e., b
‘d' + ‘s' = 3 + 18 = 21 (mod 26) i.e., v
‘i' + ‘t' = 8 + 19 = 1 (mod 26) i.e., b
Since the plaintext is longer than the keyword, keyword is repeated till all letters of the plaintext are encrypted. As it can be seen, a particular letter of the plaintext may be encrypted with different letters from the keyword. For example, the first occurrence of letter ‘i' from the plaintext is encrypted with ‘h', where its second and third occurrences are encrypted with letters‘t', and ‘o' respectively. That is, Vigen´ere cipher is a polyalphabetic substitution cipher.
To break a polyalphabetic substitution cipher, the cryptanalyst must first determine the period (i.e., the key-length) of the cipher. This can be done using two main tools: the Kassiski method, and the index of coincidence. Here we explain Kassiski method, you may search the Internet for the index of coincidence method.
The Kassiski method uses repetitions in the ciphertext to give clues to the cryptanalyst about the period. For example, suppose the plaintext ‘to be or not to be' has been enciphered using the key ‘now', producing the ciphertext below:
Plaintext t o b e o r n o t t o b e
Keyword n o w n o w n o w n o w n
Cryptogram g c x r c n a c p g c x r
In the given cryptogram (i.e., g c x r c n a c p g c x r) contains the pattern g c x r which is repeated and the distance of repetition is 9. This could be the sign in which the same letters from plaintext is encrypted with the same letters from the keyword. Since in Vigen´ere cipher the keyword is repeated, the key-length is probably 9 or a divisor of 9 (i.e., 3, because 9 has no other divisor). Assuming that the key length is 3, we split the cryptogram into three cryptogram. That is, the 1st, 4th, 7th, ... characters of the cryptogram are the result of the shift of the 1st, 4th, 7th, ... characters of the plaintext where the shift is the first letter of the keyword. Similarly, the 2nd, 5th, 8th, ... letters build another list. That is, this Vigen´ere cipher is a combination of 3 Caesar cipher.
Your Task:
In the following you can find 10 cryptograms, that are created by Vigen´ere cipher, where the plaintext is English text and the keyword is meaningful English word. You are required to decipher the cryptogram that matches with your Student-ID.
Attachment:- Townsville-and-Cairns.pdf