As hacker, on a mission deep inside an enemy installation, you have gained brief temporary access to a secret chip, which contains a hardware implementation of the DES encryption algorithm, along with...

As hacker, on a mission deep inside an enemy installation, you have gained brief temporary access to a secret chip, which contains a hardware implementation of the DES encryption algorithm, along with a single secret key. You connect the chip to your bullet-proof laptop and quickly manage to encrypt a few thousand 64-bit plaintext blocks of your choice, and record the resulting 64-bit ciphertext blocks. You are unable to directly read out the DES key K used in the chip to perform these encryptions and you will not be able to leave the site without knowing K. But you know that all S-boxes in the last DES round are supplied in this chip via a separate powersupply pin. When you create a short-circuit on that pin, the encryption progresses as normal, except that the output of all S-boxes in the last round changes to zero. a) Explain briefly the role of an S-box and the structure of a single round in DES. b) How can you find K, considering that your available time and computing power will not permit you to search through more than 109possible keys?