Question 50

a) 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).

b) A sequence of packets are transmitted back to back from a source to a destination through a wide area network.

i) Is it possible for these packets to be received at destination in an order that is different form that in which it is transmitted? Explain.

ii) If the sour and destination are in the same local area network, can these packets arrive to the destination out of order?