Assignment No. 02

Semester: Spring 2018
Network Security-CS315


Total Marks: 20


Due Date: 04/06/2018


Please read the following instructions carefully before submitting assignment:

§  You will submit your assignment before or on due date on VU-LMS.

§  Assignment should be completed by your own efforts it should not be copied from internet, handouts or books.

§  You should submit your .doc File via assignment interface at VU-LMS.

§  Assignment sent via Email will not be replied and accepted in any case.

§  If the submitted assignment does not open or file is corrupt, it will not be marked.

§  You will submit solution only in document (.doc or .docx) File.



To build the proper understanding of following topics:

a)    Hash Function

b)    Encryption Algorithm


For any query about the assignment, contact at

Assignment Questions


Question :                                                                                                                                                 Marks 20    


Part a)  10 marks


Suppose a hacker is trying to attack a secure hash function. Calculate the following to know the level of effort required by hacker if the hash code is of length ‘16’:

·         Pre-image resistant

·         Second pre-image resistant          

·         Collision resistant



Part b)  10 marks


Consider a very simple symmetric block encryption algorithm in which 32-bits blocks of plaintext are encrypted using a 64-bit key. Encryption is defined as


C = (P ⊕ K0) + K1


Where C  = ciphertext,


K secret  = key,


K0  = leftmost 64 bits of K,


K1  = rightmost 64 bits of K,


⊕ = bitwise exclusive OR,


+ and is addition mod 264.


i. Show the decryption equation. That is, show the equation for P as a function of C,

K0, and K1.


ii. Suppose and adversary has access to two sets of plaintexts and their corresponding

ciphertexts and wishes to determine K.We have the two equations: C (P K0) K1; C' (P' K0) K1


First, derive an equation in one unknown (e.g., K0). Is it possible to proceed further to solve for K0?






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