Answer Happy

Problem 6: Consider the following authentication protocol using a keyed hash function: m||ht(m) Aliece Bob, where m is the message from Alice to Bob and k is the secret key shared by Alice and Bob. We assume that the message is transmitted via a public communication channel, and that an enemy can modify transmitted messages and insert his own messages into the communication channel. 2 Let Dk be the decryption transformation of a one-key cipher and h be a hash function. Assume that the one-key cipher is secure and the hash function h is well designed in the sense that it has the weak collision resistance property and is one-way. We construct two keyed hash functions. The first one is hi!) := ho Dzo Dk; and the second one is h.2) : := Dk Doh, where o denotes the function composition. Consider the following two statements: (1) This authentication scheme with his less secure than the authentication scheme with ha (2) This authentication scheme with his less efficient than the authentication scheme with 10 marks Which of the following statements is true? (A) Statement (1) is true, but Statement (2) is false. (B) Statement (2) is true, but Statement (1) is false. (C) Both Statements (1) and (2) are true. (D) Both Statements (1) and (2) are false.