Question

Alice wants to send a single bit of information (a yes or no) to Bob using a 2-bit word for each message. There are four possible keys available for message authentication. If the matrix shows the 2-bit word sent for each message under each key, what is the most critical factor in ensuring secure communication between Alice and Bob?

a) The length of the 2-bit word
b) The number of possible keys
c) The type of information (yes or no)
d) The authentication matrix used
(Note: The correct answer represents the most critical factor for ensuring secure communication in the context provided.)

Answer 1

The most critical factor in ensuring secure communication between Alice and Bob using a 2-bit word and four possible keys for authentication is the authentication matrix used.

Step-by-step explanation:

When considering how Alice can securely communicate a single bit of information to Bob using a 2-bit word with four possible keys for message authentication, the most critical factor is d) The authentication matrix used. The length of the 2-bit word (a) is not sufficient for strong security. The type of information, being a simple yes or no (c), does not contribute to the security aspect. While having multiple keys (b) is important, the way those keys are used within the authentication matrix—dictating how messages are encoded under different keys—is the crucial element for security as it defines the actual process that ensures only someone with the correct key can authenticate the message accurately.

Answer 2

The most critical factor in ensuring secure communication between Alice and Bob is the authentication matrix used, as it dictates the secure encoding and decoding of messages.

Step-by-step explanation:

The question asks what is the most critical factor in ensuring secure communication between Alice and Bob when Alice wants to send a message using a 2-bit word with four possible keys for message authentication. Considering the options provided, the length of the 2-bit word (a) is less significant because longer words alone do not necessarily enhance security. The type of information (c) is also not critical to security as it doesn't affect the encryption or authentication mechanisms. The most critical factor in ensuring secure communication in this context is (d) The authentication matrix used. The authentication matrix defines how messages are encoded and decoded under each key, and having a secure, unpredictable encoding under each key is vital for preventing unauthorized interception or forgery of the messages.