Explain why CBC mode encryption cannot be parallelised, but decryption can be parallelised.

Write down decryption in CBC mode, and give a detailed explanation why it works

Which one of the following is not a mode of operation for the Data Encryption Standard?Question 3Answera.AESb.OFBc.CBCd.CFB

Let IV, c1, c2, c3, . . . be a CBC-mode encryption of message m1, m2, m3, . . . , where each message block mi is n-bits long. Suppose an attacker (who does not know the key) knows the first block m1 (e.g., it is predictable header information). Suppose m01 is a different n-bit string. Show how the attacker can make a new ciphertext IV 0 , c01 , c02 , c03 , . . . which decrypts to m01 , m2, m3, . . . , even though they do not know the key that was used for the encryption.

To encrypt a series of plaintext blocks p1, p2, . . . pn using a block cipherE operating in electronic code book (ECB) mode, each ciphertext blockc1, c2, . . . cn is computed as ci = Ek(pi).Which of the following is not a property of this block cipher mode?a.Noneb.Any repeated plaintext blocks will result in identical corresponding blocksciphertext blocks.c.Decryption can be fully parallelizedd.If a ciphertext block is modified or corrupted, then after decryption thecorresponding plaintext block and all the following plaintext blocks willbe affected.

The purpose of parallel processing is to speed up the computer processing capability and increase its -------------. [ LO32 ] [ L1 ] [KL]*ComplexityThroughputNoneCost