Midterm Exam Solutions

Midterm Exam SolutionsCS161 Computer Security, Spring encrypt a series of plaintext blocksp1,p2,..pnusing a block cipherE operating in electronic code book (ECB) mode, each ciphertext blockc1,c2,..cnis computed asci= Ek(pi).Which of the followingis nota property of this block cipher mode?(a) Any repeated plaintext blocks will result in identical correspondingciphertext blocks.(b) Decryption can be fully parallelized.(c) If a ciphertext block is modified or corrupted, then after decryption thecorresponding plaintext block and all the following plaintext blocks willbe affected.(d) None of the above; that is, (a), (b), and (c) are all properties of theECB block cipher :The correct answer is (c). In ECB, altering a ciphertext blockonly affects a single plaintext encrypt a series of plaintext blocksp1,p2,..pnusing a block cipherE operating in cipher block chaining (CBC) mode, each ciphertext blockc1,c2,..cnis computed asci= Ek(pi ci 1), wherec0is a public initializa-tion vector (IV) which should be different for each encryption of the followingisa property of this block cipher mode?

Midterm Exam Solutions CS161 Computer Security, Spring 2008 1. To encrypt a series of plaintext blocks p 1;p 2;:::p n using a block cipher E operating in electronic code book (ECB) mode, each ciphertext block

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