Question

What is the correct 2-bit word sent by Alice to Bob for message authentication, given the available keys?

Key 1: 00
Key 2: 01
Key 3: 10
Key 4: 11
a) If Alice wants to convey "Yes"
b) If Alice wants to convey "No"

Choose the correct answer.

Answer 1

Without additional context to link the keys to their respective meanings, it is impossible to determine which 2-bit code Alice would send to convey 'Yes' or 'No' for message authentication. The keys represent an agreed-upon code between Alice and Bob to ensure secure communication.

Step-by-step explanation:

The information provided in the question appears to be part of a communication protocol using symmetric key cryptography, where 2-bit codes are used to represent specific messages. If Alice wants to send a confirmation message to Bob, she would use a predefined key that Bob is able to recognize as 'Yes'. Conversely, to send a negative response, she would use a different predefined key that Bob recognizes as 'No'. However, the question does not specify which keys are associated with 'Yes' or 'No'. In practice, these keys would be agreed upon in advance and kept secret between Alice and Bob to ensure message authentication.

Example:

If Key 1 corresponds to 'Yes', then Alice would send '00'.
If Key 3 corresponds to 'No', then Alice would send '10' to convey the message 'No' to Bob. These are just examples, as the real keys used would depend on their pre-arranged agreement.