# Foundations of Cryptography | NPTEL | Week 4 Assignment Solutions

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### Foundations of Cryptography NPTEL Week 4 Assignment Solutions

Q1. Which of the following is/are false about modes of operation?

a) A sequence of n messages can be encrypted using block cipher by making less than n calls to a secure PRF
b) Cipher-text computation is parallelizable in CTR mode.
c) Plain text of any length can be encrypted in OFB mode
d) Stateful variant of Counter mode is secure where as that of OFB mode is insecure

Q2. Consider the stateless variant of CBC-mode of encryption with a block cipher having a 256-bit key and 128-bit block length to encrypt a 512-bit message. The length of the resulting ciphertext in bits is:

a) 256
b) 128
c) 640
d) None of these

Q3. Which of the following is(are) true about Feistel and SPN networks?

a) SPRP can be constructed using 4-round Feistel network
b) Diffusion is used to produce avalanche effect in an SPN
c) S-boxes are used to produce confusion in an SPN
d) All of these

Q4.

a)is a secure PRF
b)

is a secure PRP
c)is a secure SPRP
d)can be used to instantiate the CTR mode of block cipher

Q5.

Foundations of Cryptography NPTEL Week 4 Assignment Solutions

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### 14 thoughts on “Foundations of Cryptography | NPTEL | Week 4 Assignment Solutions”

1. Please provide all week answers,…if you are not sure still provide, atleast we get little clarity and place to discuss the questions and their subjective answers. Otherwise solving assignments like these, is really a monotonous activity prone to lots of misconceptions…

1. Please also send week-6 answers. Atleast we can verify the concept understanding. If too late then it is difficult to check the concepts the answers.