.

**Note:** Take your time and provide well-articulated answers. Detailed explanation and full solutions are required to obtain a passing grade.

**A.** To confirm accuracy – to a certain extent – a binary message of 256 bits in length will be accompanied by a 16-bit hash code. How many such messages would be sharing the same hashcode value?

**B.** What is the purpose of the Diffie-Hellman algorithm? What are its major strength(s) and weakness(es)?

**C**. Define the encryption concept steganography, and describe the principle on which it is based on.

**D **. Data vs. Information. Provide examples where they are the same and where they are different.

**E** . Compare and contrast symmetric and asymmetric encryption algorithms. Present a brief overview of the cryptographic basis for each type of algorithm, and a comparison of their relative strengths and vulnerabilities. Describe how a hacker might go about cracking a message encrypted with each type of algorithm. Suggest a specific application for each type of algorithm where the advantages clearly outweigh the disadvantages.

**F.** An Enigma ** **http://enigmaco.de/enigma/enigma.html** **encrypted message was intercepted and reads as follows:

**OTIBDHEMUOFGMFMHGKMGNDOEGIBBKXZEJWR **

A *sleeper* of ours behind enemy lines sent a message that the enemy’s encryption used Rotor1: **Z** and Rotor3: **E** . Decrypt the message.

**G.** An encryption algorithm turned **GOOD MORNING AMERICA** into **FNNC LNQMHMF ZLDQHJZ **Identify the encryption algorithm and express it in a mathematical form.

**H** . What is the meaning of electronic *signing* a document? What does the “the signature” look like? Provide an explanation.

**I** . A certain cryptography vendor was providing an encryption technology that was breakable within one hour**. **Considering the continuous increase in computer speed, the company decided to increase the size of the encryption key so that the time to break the encryption become more than 250 hours. What should be the minimum key size increase to meet this objective, considering that in this encryption technology, the increase of a single bit in the size of the encryption key doubles the amount of needed computations.

**J **. The following enemy encrypted message has been intercepted:

**YJRNP<NSTTF<RMYEO::DYSTYYP<PTTPE **A *sleeper* of ours behind enemy lines sent a message that the enemy’s encryption had to do with the QWERTY keyboard layout. Decrypt the message and save lives.