Question # 5.

a. Pretty Good Privacy (PGP) is broadly used to secure email communication. Explain the steps needed prior to exchanging email messages with privacy and authenticity guarantees for a pair of users using PGP.

b. Estimate the time required to crack a 56-bit DES key by a brute-force attack using a 3000 MIPS (million instructions per second) computer, assuming that the inner loop for a brute-force attack program involves around 15 instructions per key value, plus the time to encrypt an 8-byte plaintext. Perform the same calculation fora 128-bit IDEA key.

Extrapolate your calculations to obtain the cracking time fora 300,000 MIPS parallel processor (or an Internet consortium with similar processing power).