WEEK

BIC3313 Internet Payment Systems

Department : Faculty of Information & Communication TechnologyCourse Name : Associate Degree in Business Information TechnologySemester : 5Commence Date: 29th, September 2014 Individual Assignment 1(20%)

Deadline Date: 6th, October 2014

1. In one of his cases, Sherlock Holmes was confronted with the following message.534 C2 13 127 36 31 4 17 21 41DOUGLAS 109 293 5 37 BIRLSTONE26 BIRLSTONE 9 127 171

Although Watson was puzzled, Holmes was able immediately to deduce the type of cipher. Can you? There will be no points for the problem if you do not show the steps.

2. Given an RSA signature scheme with the public key (n = 9797, e = 131). Is this signature valid? x = 4333, sig(x) = 1424. Show all intermediate steps of the algorithm you are using. There will be no points for the problem if you do not show the steps. 3. Compute the private key for the RSA scheme with the following parameters: p =33, q = 11, e = 17. Show all intermediate steps of the algorithm you are using. There will be no points for the problem if you do not show the steps.

4. One important aspect of digital signatures is the computational effort required to (i) sign a message, and (ii) to verify a signature. We will study the computational complexity of the Elliptic Curve algorithm with the public key (p,a,b,q,A,B) used as a digital signature in this problem.(a) How many point additions and doublings do we need on average to perform (i) signing of a message and (ii) verification of a signature? Assume that q has l = log2 q bits. (b) What takes longer, signing or verification?

5.Using the online AES encryption/decryption tool at http://cryptojs.altervista.org/secretkey/aes_cryptojs.html , answer the following questions:Encrypt your name and your home address using all the five modes ECB, CBC, OFB, CFB and CTR, and the padding options NoPadding, ZeroPadding and PKCS7.

Indicate the differences between the resulting ciphertexts and explain the differences between the padding schemes. Notice that you can set the IV and Salt to any value including 0.

Explain the purpose of the Salt. What is the difference between the Salt and the Padding?

5. Online encryption/decryption tools http://cryptojs.altervista.org/E. Styer's encryption/decryption tools http://people.eku.edu/styere/

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