Explain how an integrity check value used

Assignment Help Computer Networking

Reference no: EM131307621

1. (a) Briefly explain how an integrity check value (ICV) may be used in network communication to detect errors.

(b) When using an ICV, explain why

(i) a message might be transmitted correctly but the receiver believes the message contains an error (a false negative).

(ii) a message might be transmitted incorrectly but the receiver believes the message is correct (a false positive).

2. Consider the following two algorithms A and B for computing an ICV: Step A1) Split the data into 7-bit chunks
Step A2) For each chunk add an 8th bit, choosing the value of the bit to be the same as the 1st bit

Using algorithm A, the 21-bit message 0001110 1010011 1110110, for example, would be transmitted as: 00011100 10100111 11101101

Step B1) Split the data into 7-bit chunks

Step B2) For each chunk add an 8th bit, choosing the value of the bit so that each 8-bit chunk contains an even number of bits with the value 1 (and hence an even number of bits with the value 0)

Using algorithm B, the 21-bit message 0001110 1010011 1110110 would be transmitted as 00011101 10100110 11101101.
For each algorithm A and B explain:

(a) How the receiver checks whether the message has been transmitted without error.

(b) Under what circumstances a false negative occurs.

(d) Carefully explain which algorithm you think is better for computing ICVs.
[Bonus question: Identify a simple mechanism for reducing the number of false positives produced by algorithm B.]

3. Consider the following protocols, Probe and Copy: Probe 1. Send "Hello" message

Probe 2. Recipient returns a string of 512 random bits to the sender

Copy 1. Send message

Copy 2. Recipient returns a copy of the message to the sender

Assuming machines A and B are each running implementations of the Probe and Copy pro- tocols, explain:

(a) How an attacker M can use Probe to cause A to send a message to B.

(b) How M can establish an endless loop of messages between A and B.

Reference no: EM131307621

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