This assignment will assess your proficiency on the impact of using DNS and need for MIME headers.

There are two parts to this assignment. And you are required to attempt both of them.

Part $1$

John and Anthony are two branch managers of a financial organization. John has a message, M$1,$ to be communicated to Anthony. For a secure communication, John wants to send message M$2$ to Anthony $($without revealing M$1$ immediately$)$ that can be used later to verify that John knew M$1$ at the time M$2$ was sent. During this later veri$$cation$,$ John may reveal M$1$ itself.

a$.$ Suppose John simply sends M$2=$ hash$($M$1).$ Explain how Anthony can quickly recover M$1.$

b$.$ There are some possibilities of attacks when John uses a simple hash function. How can John construct M$2$ using a secure$-$hash function, avoiding the problem of those attacks? Hint: as part of the later veri$$cation$,$ John can supply additional information to Anthony.