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CS572AH2 Computer Security Homework-3 Assignment SP 2021 _____________________________________________________________________________________________

	CS572AH2 Homework-3 Assignment
	Send your HW3 Report electronically

Student’s Name: ___________________

Show all your work in detail for the highest grade. Good luck!

1. (15 pts.) Consider the mod 10 multiplication table (see the table on the right, below):

a. Which rows contain a value of 1? {in increasing numerical order} ____, ____, ____, ____.

b. These rows and no others contain a value of 1 because they are the only ones that are ________ to 10.

c. These numbers are significant for mod-10 arithmetic because only these numbers have ______, mod 10.

2. (10 pts.) [Fill out your answers {a function name and a number} directly in the text]: In the Number Theory, two integers, n and m, are said to be relatively prime (or co-primes) when their ____(n, m) {a function} = _____{a number}.

3. (10 pts.) [Message Authentication Codes] Bob sends a message to Alice. He sends the message in plaintext, but first he uses a Message Authentication Code (MAC), with a secret key he shares with Alice, to create a cryptographic checksum for the message. He sends the cryptographic checksum along with the message. Upon receipt of the message, Alice uses the same MAC algorithm and key to generate a cryptographic checksum. She compares the two checksums and finds them to be identical. As a result, what two things is Alice assured of about the message? _______________ What is she not assured of? ______________________

4. (15 pts.) What is the essential difference between a worm and a virus? Your Answer: _________________

5. (15 pts.) [Fill out your answers directly in the text]: Sometimes, web pages contain tiny images, too small to be visible to the user. Such an image is called a ___________, and its purpose is to convey information to a web server operated by a company that ___________ your navigation through the web.

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