QUESTION
Alice wants to send a single bit of information (a yes or no) to Bob by means of a word of length 2. Alice and Bob have 4 possible keys available to perform message authentication. The following matrix shows the 2-bit word sent for each message under each key: \begin{tabular}{|r|c|c|} \hline & Message & \\ \hline Key & 0 & 1 \\ \hline 1 & 00 & 01 \\ \hline 2 & 10 & 00 \\ \hline 3 & 01 & 11 \\ \hline 4 & 11 & 10 \\ \hline \end{tabular} A. What is the probability that someone else can successfully impersonate Alice? B. What is the probability that someone can replace an intercepted message with another message successfully?
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