Explain why in the Counter (CTR) mode the encryption of different blocks  can be done in parallel. For each of problems 2 - 4 your explanations  an include a drawing of the encryption and decryption procedure.

Explain the difference between a secure cipher, a CPA-secure cipher, and a CCA-secure cipher. Under what conditions do we need i) CPA security? ii) CCA security?

Encrypting with TDEA and a single key is pointless, because it is equivalent to encrypting with the original "single" DES, which is no longer considered strong enough to resist feasible attacks. In your own words (do not quote in any way from any source), briefly explain why decrypting with TDEA and a single key was a useful operation when TDEA was developed.