The Gateway to Computer Science Excellence
First time here? Checkout the FAQ!
+15 votes

Consider the following two statements:

  1. A hash function (these are often used for computing digital signatures) is an injective function.
  2. A. encryption technique such as DES performs a permutation on the elements of its input alphabet.

Which one of the following options is valid for the above two statements?

  1. Both are false
  2. Statement (i) is true and the other is false
  3. Statement (ii) is true and the other is false
  4. Both are true
asked in Computer Networks by Boss (19.1k points) | 1.4k views

3 Answers

+19 votes
Best answer

Answer is C.

i. Hash function is not one one or injective. It is many to one.

ii. True. Uses P-Box permutation.

answered by Boss (34.1k points)
edited by
0 votes

Option (i) Here some asymmetrical algorithms where we apply Hashing (Hashing is a method used to verify data integrity).

1. RSA - named after Rivest, Shamir, and Adleman (investor)

2. Diffie-Hellman (DH)

3. ElGamal - based on the DH echange 

4.Digital Signature Algorithm (DSA)- created by NSA 

5. Eliptic Curve Cryptography (ECC)

Here some most popular Hashing types

1. MD5 (Message Digiest 5)

2. SHA 1

3. SHA 2

4. SHA 3

So we can correctly say it is not injective (one to one).

Option (ii) DES (Digital Encryption Standard) is part of symmetric key algorithm where we use same key to encrypt the data and decrypt the data. so calculating we perform permutation.

Statement (ii) is true and the other is false


answered by (299 points)
edited by
–5 votes
ans d)
answered by Active (5.2k points)

The hash function (these are often used for computing digital signatures) such as MD5 and SHA are not injective, a perfect hash function will be injective so i wonder what the answer should be.


Answer is (C)

During hash generation more than one message may generate the same HASH value( why should we talk about only about perfect hashing ;That is more than some specific thing !!).So hash function is Many-to-One

makes sense.

Related questions

Quick search syntax
tags tag:apple
author user:martin
title title:apple
content content:apple
exclude -tag:apple
force match +apple
views views:100
score score:10
answers answers:2
is accepted isaccepted:true
is closed isclosed:true

36,995 questions
44,571 answers
43,637 users