1. Decryption Speed

A certain cryptography vendor was providing an encryption technology that was breakable within 10 hours. 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?

Hint: Normally, the increase of a single bit in the size of the encryption key doubles the amount of needed computations.

2. Diffie-Hellman

You have agreed with your friend X that you will use the Diffie-Hellman public-key algorithm to exchange secret keys. You and X have agreed to use the public base g = 19 and public modulus p = 739. You have secretly picked the value SA = 5. You begin the session by sending X your calculated value of TA. X responds by sending you the value TB = 167. What is the value of your shared secret key? Show all your work.

3. Encryption

In a given encryption system where the messages are expressed only as numbers and "e" is an integer.

cyphertext = Part One: {int[(plaintext)^(1/e)]} Part Two: {plaintext -
{int [(plaintext)^(1/e)]}^e}

Show how the recipient of the message, who knows "e", produces the plaintext.