a) Suppose your professor wanted to distribute some code to all members of your
ID: 3743936 • Letter: A
Question
a) Suppose your professor wanted to distribute some code to all members of your class. Assume your professor is unquestionably trustworthy. Your professor invents a scheme by which she will denote that her code is safe to use. Before distributing the code, she will send a not to everyone saying she is about to post program P1, so when you find P1 on your class's server you can trust it. How could Mel, a malicious student, sneak in his own malicious code under that model?
b) Continuing the previous question, suppose your professor added that the first 4 bytes of P were abcd. How could Mel sneak in his code under that model?
Explanation / Answer
Answer)
a)
The professor wanted to distribute some code to all members of your class and the professor is unquestionably trustworthy. To make sure that the code she sends is safe to use, Before distributing the code, professor will send a not message to everyone saying she is about to post program P1, so that P1 program when received by everybody is trustworthy. Mel is a malicious student whose intention will be to sneak in the malicious code instead of the program P1.
What Mel can do is:
Mel can send the 'not' message to everyone in the class, pretending to be the processor, when the professor is trying to send the message to the class, and thus Mel's malicious program will be distributed to all in the class. This is a way in which Mel, a malicious student, can sneak in his own malicious code under that model.
b)
Let P is the program which the professor is wanting to distribute. The first four bytes of P is abcd, as the professor says, so it's a check when the first four bytes of P is abcd, it means that the program has come from genuine sources and can be trusted.
What Mel can do in the regard also is:
Mel can modify his malicious program so that, the first 4 bytes of the malicious program also is abcd, in that case, the students will expect that the malicious program is the genuine program and trust it, as the first 4 bytes of P were abcd. This way also Mel can sneak in his code under this model.
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