1: Bob believes that he has come up with a nifty hash function. He assigns a numeric value VChar to each letter in the alphabet equal to the letter's position in the alphabet, i.e., VA = 1, VB = 2, ..., VZ = 26. For a message, he calculates the hash value H = (VChar 1 x VChar 2 x VChar 3 ...x VChar N) mod(26).
Bob uses this function to send a one-word message, GLARE, to his banker Bill, along with his calculated hash value for the message. Alice is able to intercept the message, and generates an alternative message that has a hash value that collides with Bob's original hash value.
Give definition and properties of the hash function.
Show a message that Alice may have used to spoof Bob's message, and demonstrate that its hash value collides with Bob's original hash.
Q2: Consider the following plaintext message: THE SIXTEENTH PRESIDENT WAS ABRAHAM LINCOLN.
- If this message is sent unencrypted and successfully received, what is its entropy? And why?
- If this message is encrypted with DES using a random 56-bit key, what is the encrypted message's entropy? And why