Question

(a) Let E be an encryption function and A a function that can be used to...

(a) Let E be an encryption function and A a function that can be used to compute a
message authentication code. Let x be a message. Alice computes E(A(x)jx) and
sends it to Bob. Is this an example of encrypt-and-MAC, encrypt-then-MAC or
MAC-then-encrypt?
(b) Let E be an encryption function and A a function that can be used to compute a
message authentication code. Let x be a message. Alice computes E(x)jA(x) and
sends it to Bob. Is this an example of encrypt-and-MAC, encrypt-then-MAC or
MAC-then-encrypt?
(c) Which of the following functions is negligible:
1/ 2n;1/2log n ;1/nlog n :
(d) Which of the following functions is not negligible:
1/2n ;1/ n-1/2n ; n/n2

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Answer #1

(c) can be solved by comparing one function with others

(d) can be solved by comparing one function with others

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