Question

Bob is stationed as a spy in Cyberia for a week and wants to prove that he is alive every day of this week and has not been captured. He has chosen a secret random number, x, which he memorized and told to no one. But he did tell his boss the value y = H(H(H(H(H(H(H(x))))))), where H is a one-way cryptographic hash function. Unfortunately, he knows that the Cyberian Intelligence Agency (CIA) was able to listen in on that message; hence, they also know the value of y. Explain how he can send a single message every day that proves he is still alive and has not been captured. Your solution should not allow anyone to replay any previous message from Bob as a (false) proof he is still alive.

Answer 1

Answer:

See explaination

Explanation:

The foremost thing to do is to produce a public key and a private key pair H+ and H-and encrypts H+ along with hash of the password ( paswrd) such as H(paswrd)(H+)

When the boss maks use the password hash to gain H+, this will produce a symmetric key P and encrypts it with H+ in the public key cryptosystem and result could be further encrypted with password hash.

If Bob employs the password hash and H- to obtain H from H(paswrd)(AEK+(H)); then he can employ H to send messages to Boss. Furthermore a signature algorithm can be employed to encrypt for signing messages.