Suppose that Bob receives Alice’s digital certificate from someone claiming to be Alice.
a. Before Bob verifies the signature on the certificate, what does he know about the identity of the sender of the certificate?
b. How does Bob verify the signature on the certificate and what useful information does Bob gain by verifying the signature?
c. After Bob verifies the signature on the certificate, what does he know about the identity of the sender of the certificate?
When encrypting, public key systems operate in a manner analogous to a block cipher in ECB mode. That is, the plaintext is chopped into blocks and each block is encrypted independently.
a. Why is ECB mode a bad idea when encrypting with a block cipher? Why is a chaining mode, such as CBC, a much better way to use a block cipher?
b. Why is it not necessary to perform any sort of chaining mode when using public key encryption?
c. Could your reasoning in part b be applied to block ciphers? Why or why not?
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