Alice want to send a single bit of information (a yes or a no) to Bob by means of a word of length 2. Alice and Bob have four possible keys avialable to perform message authentication. The following matrix shows the 2-bit word sent for each message under each key:

a. The preceding matrix is in a useful form for Alice. Construct a matrix with the same information that would be more useful for Bob.

b. What is the probability that someone else can successfully impersonate Alice?

c. What is the probability that someone can replace an intercepted message with another message successfully?

Transcribed Image Text:

Key 1 2 3 4 0 00 10 01 11 Message 1 01 00 11 10