Hint to the solution 3. Suppose that two countries A and B want to reach an agre

Question

Hint to the solution

3. Suppose that two countries A and B want to reach an agreement to ban underground nuclear tests. Neither country trusts the other, in both cases for good reason. Nevertheless, they must agree on a system of ver- ification devices to be implanted at various locations on the territory of the two countries. Each verification device consists of a sophisticated seismograph, a small computer for interpreting the seismograph read- ing and generating a message, and a radio transmitter. Explain how public key cryptography can be used to enable all of the following (at first glance seemingly contradictory) conditions to be met: a. Country A insists on knowing the plaintext content of all messages emanating from its territory, in order to be sure that the devices are not used in coordination with espionage activities by Country B b. Country B insists that Country A cannot fabricate a message from the devices which broadcast from its territory (i.e., a message saying that everything's OK, when in fact the seismograph has detected a treaty violation) c. Country A insists that, if Country B falsely claims to have received notification from the device of a treaty violation, then any interested third country will be able to determine that, in fact, no such message was sent.

Explanation / Answer

From the HInt, we can take that the example requires implementation of a scheme similar to a digital signature, where everyone has the key required for decryption, but only the sender has the key that can encrypt.

a.) Country A can decrypt the messages it sends as KD is known to everyone.

b.) Country B should not worry if the hinted public key cryptosystem is agreed upon. Country A do not possess the encyption key of country B. So it will not be able to create a message that can be deciphered by the decryption key of country B.

c.) The use of the random integers ensures that a country can not fabricate messages without the encryption key. The encryption key is known to the device only. This ensures non-repudiation as well as prevents forgery. So a country can not claim to have a messgae recieved when infact no such message was sent by the device.

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.