Question

Try to make it as simple as you can and explain as much as it needed.

1. Define Integrity and Nonrepudiation? (2 points)

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2. What are the differences between Stream Cipher and Block Cipher? (2 points)

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3. What is Access Control and why is it important? (2 points)

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4. Message Authentication Code ensures authentication or integrity or both? Justify and explain your answer. (3 points)

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5. What are the weaknesses of DES? Why triple DES is better than Double DES? (3 points)

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Answer 1

1)Integrity is that the data gets protected from an unauthorised changes and to ensure that is is reliable and also its correct.

The file is protected so that no one else could use it as its very important.

Non repudiation is the assurance in which that someone cannot deny the validity of something.

Suppose A sends a file to B then A cannot deny that he have not sent the file and also B cannot deny that it have not recieved the file.

2)difference between block cipher and stream cipher

Block cipher will be converting the plain text into cipher text by taking the plain texts block at a time	stream cipher will convert the plain text into cipher text by taking 1 byte of plain text at a time.
Block cipher will use either 64 bits or more than 64 bits	while the stream cipher uses 8 bits
The complexity of block cipher is simple	while the complexity of stream cipher is more complex.

3) Access control is the approach to the computer security like antivirus, and host intrusion and prevention or the user or the system authentication and the network security system is

It is important so that the system gets protected from unwanted virus and hackers. The This keeps the insecure devices from accessing and also affecting the network. It allows only the users who have authority to use the system.

4) message authentication code ensures the integrity and also the authentication both. It allows the the verifiers to be who possess the secret key to detect any changes to the message content. It confirms that the message is come from the sender ie., and the authentication and has not been changed.

5) weakness of DES- there are few weakness in the in DES when the key selected are weak keys. These keys might be avoided. The DES have proved to be very well designed block cipher. There have been no significant crltanalytic attacks on the DES and than the exhaustive key search.

Triple DES is better than double DES because the triple DES uses the three instance of DES on the same plain text. It uses 3 different types of key choosing techniques in first l the keys are different and in second two keys are same and one is different and in third all keys are same. Triple DES is also vulnerable to meet in the middle attack.