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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.

1.

DSA protocol is based on(a) Discrete logarithm problem(b) Continuous logarithm problem(c) Discrete & Continuous logarithm problem(d) None of the mentionedI had been asked this question in an internship interview.I want to ask this question from Pretty Good Privacy topic in section Encryption and Decryption of Digital Communications

Answer»

Correct option is (a) Discrete LOGARITHM problem

Explanation: The DSA algorithm uses and is BASED on discrete logarithm problem.
Discussion
2.

The hash function(a) Is collision free(b) Has manageable collision(c) Has high unmanageable level of collision(d) None of the mentionedThis question was addressed to me by my college professor while I was bunking the class.Query is from Pretty Good Privacy topic in section Encryption and Decryption of Digital Communications

Answer» CORRECT answer is (a) Is COLLISION FREE

Explanation: Hash function is collision free and it is UNFEASIBLE that two different messages will create the same hash value.
Discussion
3.

In hash function output length is fixed.(a) True(b) FalseThis question was posed to me in an internship interview.My query is from Pretty Good Privacy topic in section Encryption and Decryption of Digital Communications

Answer»

Correct choice is (a) True

The BEST EXPLANATION: In hash function the OUTPUT length is fixed and it is EASY to COMPUTE.
Discussion
4.

The digital signature provides authentication to the(a) Sender(b) Message(c) Sender & Message(d) None of the mentionedI had been asked this question in homework.I want to ask this question from Pretty Good Privacy topic in chapter Encryption and Decryption of Digital Communications

Answer»

Correct answer is (c) Sender & MESSAGE

The best I can explain: The DIGITAL SIGNATURE PROVIDES authentication to both the sender and the message.
Discussion
5.

Which should be used first to decrypt?(a) Public key(b) Private key(c) Public & Private key(d) None of the mentionedThis question was addressed to me in an interview.This interesting question is from Pretty Good Privacy in portion Encryption and Decryption of Digital Communications

Answer»

Correct OPTION is (b) Private key

For explanation I WOULD say: The RECIPIENT should first decrypt the message using private key and then with the public key.
Discussion
6.

Which algorithm is used for public key encryption?(a) RSA(b) Diffie-Hellman(c) RSA & Diffie-Hellman(d) None of the mentionedThe question was posed to me in semester exam.Question is taken from Pretty Good Privacy in chapter Encryption and Decryption of Digital Communications

Answer»

The CORRECT ANSWER is (C) RSA & Diffie-Hellman

To elaborate: The two algorithms used for PUBLIC key encryption in PGP are RSA and Diffie-Hellman algorithms.
Discussion
7.

What is the key size allowed in PGP?(a) 1024-1056(b) 1024-4056(c) 1024-4096(d) 1024-2048I got this question by my school principal while I was bunking the class.This question is from Pretty Good Privacy in chapter Encryption and Decryption of Digital Communications

Answer»

Correct answer is (C) 1024-4096

The explanation: Pretty good privacy SECURITY system allows 1024 to 4096 BITS of KEY size.
Discussion
8.

Which operation is used in encryption using IDEA?(a) Addition modulo 216(b) Bit wise XOR(c) Addition modulo 216 & Bit wise XOR(d) None of the mentionedThe question was posed to me in an online interview.This intriguing question comes from Pretty Good Privacy in division Encryption and Decryption of Digital Communications

Answer»

The correct choice is (C) Addition modulo 216 & Bit wise XOR

The best explanation: The ARITHMETIC operations used in IDEA are addition modulo 216, MULTIPLICATION modulo 216+1, and bit wise XOR.
Discussion
9.

The key size of DES is(a) 56 bits(b) 64 bits(c) 128 bits(d) 168 bitsI have been asked this question in a national level competition.This key question is from Pretty Good Privacy topic in section Encryption and Decryption of Digital Communications

Answer»

Right answer is (a) 56 bits

The EXPLANATION is: The key SIZE of DES algorithm is 56 bits and with Triple-DES, the message to be encrypted is run on DES algorithm 3 TIMES.
Discussion
10.

These three ciphers can operate of ______ of plaintext and cipher text.(a) 128 bit blocks(b) 64 bit blocks(c) 256 bit blocks(d) 156 bit blocksThe question was asked in an interview.I'd like to ask this question from Pretty Good Privacy topic in chapter Encryption and Decryption of Digital Communications

Answer»

Correct CHOICE is (b) 64 bit BLOCKS

The EXPLANATION is: The three ciphers – Triple-DES, IDEA and CAST can operate on 64 bit blocks of plain TEXT and cipher text.
Discussion
11.

Which block cipher has key length of 128 bits?(a) IDEA(b) CAST(c) IDEA & CAST(d) None of the mentionedThe question was asked during an internship interview.My question comes from Pretty Good Privacy in section Encryption and Decryption of Digital Communications

Answer»

Correct choice is (c) IDEA & CAST

For explanation: The BLOCK CIPHERS IDEA and CAST has key length of 128 bits where as Triple-DES has key SIZE of 168 bits.
Discussion
12.

PGP offers _____ block ciphers for message encryption.(a) Triple-DES(b) CAST(c) IDEA(d) All of the mentionedThis question was posed to me in an interview for internship.My question comes from Pretty Good Privacy in division Encryption and Decryption of Digital Communications

Answer»

Correct option is (d) All of the mentioned

To EXPLAIN: Pretty good privacy security SYSTEM OFFERS three block ciphers for message encryption – Triple-DES, IDEA and CAST.
Discussion
13.

For digital signatures private key cryptosystem is used.(a) True(b) FalseI have been asked this question during a job interview.This intriguing question comes from Pretty Good Privacy in chapter Encryption and Decryption of Digital Communications

Answer» CORRECT CHOICE is (b) False

To elaborate: Public key CRYPTOSYSTEM is used for the CREATION of digital SIGNATURES.
Discussion
14.

Data compression includes(a) Removal of redundant character(b) Uniform distribution of characters(c) Removal of redundant character & Uniform distribution of characters(d) None of the mentionedThis question was posed to me during an internship interview.I want to ask this question from Pretty Good Privacy topic in division Encryption and Decryption of Digital Communications

Answer»

Correct choice is (c) Removal of REDUNDANT CHARACTER & Uniform distribution of CHARACTERS

Easiest explanation: Data compression removes redundant character strings in a file and PRODUCES a more uniform distribution of characters.
Discussion
15.

Public key cryptosystem is used for the encryption of(a) Messages(b) Session key(c) Session key & Messages(d) None of the mentionedI had been asked this question during an interview for a job.I would like to ask this question from Pretty Good Privacy in portion Encryption and Decryption of Digital Communications

Answer»

The CORRECT CHOICE is (b) Session key

To explain I would say: PUBLIC key cryptosystem is used for encryption of MESSAGES and private key cryptosystem is used for encryption of messages.
Discussion
16.

Pretty good privacy (PGP) security system uses(a) Public key cryptosystem(b) Private key cryptosystem(c) Public & Private key cryptosystem(d) None of the mentionedThis question was addressed to me during an interview.The above asked question is from Pretty Good Privacy in chapter Encryption and Decryption of Digital Communications

Answer»

The correct choice is (c) PUBLIC & Private key cryptosystem

The explanation: PGP USES many encryption techniques such as private key cryptosystem and ALSO public key cryptosystem.
Discussion
17.

Euler’s totient function is determined by(a) pq(b) (p-1)(q-1)(c) (p+1)(q+1)(d) p/qI had been asked this question in semester exam.This is a very interesting question from Public Key Cryptosystems in section Encryption and Decryption of Digital Communications

Answer» CORRECT choice is (b) (P-1)(Q-1)

Explanation: The Euler’s totient FUNCTION is determined by (p-1)(q-1), where p and q are kept hidden.
Discussion
18.

Which should be kept as a secret in public key cryptosystem?(a) Encryption key(b) Decryption key(c) Encryption & Decryption key(d) None of the mentionedThe question was asked in an internship interview.The doubt is from Public Key Cryptosystems topic in division Encryption and Decryption of Digital Communications

Answer»

Correct choice is (b) DECRYPTION key

The best I can explain: In public key cryptosystem, decryption key NEEDS to be KEPT as a secret.
Discussion
19.

Public key cryptosystem is also known as(a) One way function(b) Two way function(c) Feedback function(d) None of the mentionedI had been asked this question in examination.My question is based upon Public Key Cryptosystems topic in portion Encryption and Decryption of Digital Communications

Answer» RIGHT choice is (a) ONE way function

For explanation: PUBLIC key cryptosystem is called as a TRAP DOOR one way function.
Discussion
20.

Public key cryptosystem uses same key for both encryption and decryption.(a) True(b) FalseI had been asked this question in an interview for job.Question is taken from Public Key Cryptosystems in division Encryption and Decryption of Digital Communications

Answer»

The correct choice is (b) False

Easiest explanation: Public KEY cryptosystem uses DIFFERENT KEYS for ENCRYPTION and decryption.
Discussion
21.

Synchronous ciphers uses(a) Confusion(b) Diffusion(c) Confusion & Diffusion(d) None of the mentionedThis question was posed to me in an international level competition.I would like to ask this question from Public Key Cryptosystems topic in division Encryption and Decryption of Digital Communications

Answer»
Discussion
22.

In which method, key-stream is generated independently?(a) Synchronous(b) Self synchronous(c) Synchronous & Self synchronous(d) None of the mentionedI got this question during an internship interview.The query is from Public Key Cryptosystems in section Encryption and Decryption of Digital Communications

Answer»

Right ANSWER is (a) SYNCHRONOUS

For EXPLANATION I would say: In synchronous ENCRYPTION system, the key-stream is GENERATED independently of the message.
Discussion
23.

In stream encryption, the key sequence repeats itself.(a) True(b) FalseThe question was asked during an interview.This intriguing question originated from Public Key Cryptosystems in division Encryption and Decryption of Digital Communications

Answer»

Right OPTION is (b) False

The explanation: In stream ENCRYPTION, random key-stream is USED. The key sequence never REPEATS.
Discussion
24.

In cipher feedback method, encryption is done on(a) Single individual bits(b) Characters(c) Single individual bits & Characters(d) None of the mentionedI have been asked this question in homework.This interesting question is from Public Key Cryptosystems in division Encryption and Decryption of Digital Communications

Answer»

The CORRECT answer is (a) SINGLE individual bits

Easiest explanation: In cipher feedback method, single individual bits are ENCRYPTED rather than characters and this leads to stream encryption.
Discussion
25.

The substitution of the letters are done(a) Serially(b) Parallel way(c) Serially & Parallel way(d) None of the mentionedThis question was addressed to me in unit test.I would like to ask this question from Public Key Cryptosystems in portion Encryption and Decryption of Digital Communications

Answer» RIGHT answer is (B) Parallel way

Explanation: The substitution PART of the encryption scheme is performed in parallel on SMALL SEGMENT of the blocks.
Discussion
26.

Cipher system can be solved effectively by statistically using(a) Time of occurrence(b) Frequency of occurrence(c) Length of the message(d) None of the mentionedThis question was addressed to me during an online exam.I want to ask this question from Public Key Cryptosystems topic in chapter Encryption and Decryption of Digital Communications

Answer»

Right answer is (b) Frequency of occurrence

The best explanation: By statistically USING the frequency of occurrence of individual characters and CHARACTER combinations we can solve many CIPHER SYSTEMS.
Discussion
27.

In transposition, the plaintext letters are(a) Substituted(b) Rearranged(c) Removed(d) None of the mentionedThe question was asked in an international level competition.This intriguing question originated from Public Key Cryptosystems in division Encryption and Decryption of Digital Communications

Answer»

Correct choice is (B) Rearranged

To explain: In permutation or transposition, the positions of the PLAINTEXT LETTERS in the message are simply rearranged.
Discussion
28.

For n input bits the number of substitution patterns are(a) 2n(b) (2n)!(c) 1/2n!(d) 2n!I have been asked this question in an interview for internship.Query is from Public Key Cryptosystems topic in chapter Encryption and Decryption of Digital Communications

Answer»
Discussion
29.

Encryption transformations are known as(a) Diffusion(b) Confusion(c) Diffusion & Confusion(d) None of the mentionedThis question was posed to me by my school teacher while I was bunking the class.This intriguing question comes from Public Key Cryptosystems in portion Encryption and Decryption of Digital Communications

Answer»

The correct ANSWER is (c) DIFFUSION & Confusion

For EXPLANATION: The encryption transformations were termed confusion and diffusion by SHANNON.
Discussion
30.

In this Merkle Hellman method same key is used for encryption and decryption.(a) True(b) FalseThis question was addressed to me during an online interview.Enquiry is from Public Key Cryptosystems in portion Encryption and Decryption of Digital Communications

Answer»

Right answer is (b) False

The EXPLANATION is: In Merkle hellman CRYPTOSYSTEM METHOD, two separate private and PUBLIC KEYS are used for encryption and decryption.
Discussion
31.

Knapsack problem can be solved by(a) Public key cryptosystem(b) Private key cryptosystem(c) Public & Private key cryptosystem(d) None of the mentionedThe question was posed to me in my homework.My question is from Public Key Cryptosystems topic in section Encryption and Decryption of Digital Communications

Answer»

The CORRECT answer is (a) Public key cryptosystem

Explanation: The KNAPSACK problem can be solved by public key cryptosystem system USING knapsack vector and data vector.
Discussion
32.

Merkle hellman is a symmetric cryptosystem.(a) True(b) FalseThe question was posed to me in examination.The origin of the question is Public Key Cryptosystems topic in division Encryption and Decryption of Digital Communications

Answer»

Right answer is (B) False

To explain: Merkell hellman CRYPTOSYSTEM is a PUBLIC key ASYMMETRIC cryptosystem method.
Discussion
33.

A set of numbers is called as super increasing if(a) Each element is greater than previous element(b) Each element greater than sum of all the previous elements(c) Each element greater than the average of all elements(d) Each element lesser than the sum of all the elementsI had been asked this question in exam.My question is taken from Public Key Cryptosystems topic in chapter Encryption and Decryption of Digital Communications

Answer»

The CORRECT option is (b) Each ELEMENT greater than SUM of all the previous elements

Explanation: A set of numbers is CALLED as super increasing if each element is greater than the sum of all the numbers lesser than it.
Discussion
34.

A cryptographic hash function has variable output length.(a) True(b) FalseThe question was asked at a job interview.This interesting question is from Public Key Cryptosystems in portion Encryption and Decryption of Digital Communications

Answer»

Right choice is (b) False

The BEST I can EXPLAIN: A cryptographic hash function has fixed OUTPUT length.
Discussion
35.

Examples of hash functions are(a) MD5(b) SHA-1(c) MD5 & SHA-1(d) None of the mentionedThe question was posed to me in an international level competition.This interesting question is from Public Key Cryptosystems topic in chapter Encryption and Decryption of Digital Communications

Answer» RIGHT option is (C) MD5 & SHA-1

For explanation: Some EXAMPLES of hash functions are MD5 and SHA-1.
Discussion
36.

Which has a key length of 128 bits?(a) IDEA(b) Triple-DES(c) IDEA & Triple-DES(d) None of the mentionedI have been asked this question in examination.Asked question is from Public Key Cryptosystems topic in division Encryption and Decryption of Digital Communications

Answer»

The correct ANSWER is (a) IDEA

For explanation I would SAY: Triple-DES uses 168 bit key size and IDEA and CAST uses 128 bits key LENGTH.
Discussion
37.

Which algorithm can be used to sign a message?(a) Public key algorithm(b) Private key algorithm(c) Public & Private key algorithm(d) None of the mentionedThis question was addressed to me in an internship interview.I'd like to ask this question from Public Key Cryptosystems in chapter Encryption and Decryption of Digital Communications

Answer»

The CORRECT choice is (a) Public key algorithm

The EXPLANATION is: Public key algorithms are used to sign a message and private key algorithms are used to encrypt the MESSAGES.
Discussion
38.

Private key algorithm is used for _____ encryption and public key algorithm is used for _____ encryption.(a) Messages, session key(b) Session key, messages(c) Can be used for both(d) None of the mentionedThis question was addressed to me in my homework.Asked question is from Public Key Cryptosystems in division Encryption and Decryption of Digital Communications

Answer»

Correct OPTION is (a) MESSAGES, session key

The best EXPLANATION: Private key algorithm is USED for encryption of messages and public key algorithm is used for encryption of session keys.
Discussion
39.

Which are called the block ciphers?(a) IDEA(b) CAST(c) Triple-DES(d) All of the mentionedI had been asked this question in a job interview.The above asked question is from Public Key Cryptosystems in section Encryption and Decryption of Digital Communications

Answer»

Right ANSWER is (d) All of the mentioned

The best explanation: Some of the EXAMPLES of block codes are triple-DES, CAST and IDEA.
Discussion
40.

PGP system uses(a) Private key system(b) Public key system(c) Private & Public key system(d) None of the mentionedThe question was posed to me during an interview.I'm obligated to ask this question of Public Key Cryptosystems in chapter Encryption and Decryption of Digital Communications

Answer»

The correct ANSWER is (c) Private & Public key system

The explanation: Pretty good privacy system uses both private key and public key BASED systems.
Discussion
41.

In public key cryptosystem which is kept as public?(a) Encryption keys(b) Decryption keys(c) Encryption & Decryption keys(d) None of the mentionedI got this question at a job interview.This interesting question is from Public Key Cryptosystems topic in division Encryption and Decryption of Digital Communications

Answer» RIGHT option is (a) ENCRYPTION keys

To explain: In public KEY cryptosystem, the encryption keys are kept as public where as decryption keys are kept as SECRET.
Discussion
42.

Pretty good privacy program is used for(a) Electronic mails(b) File encryption(c) Electronic mails & File encryption(d) None of the mentionedI have been asked this question in an online interview.I want to ask this question from Public Key Cryptosystems in chapter Encryption and Decryption of Digital Communications

Answer»

Correct answer is (c) Electronic MAILS & File encryption

The explanation is: PRETTY good privacy (PGP) privacy program is USED for both electronic mails and file encryption.
Discussion
43.

In a trapdoor function, the functions are easy to go in(a) One direction(b) Two directions(c) All directions(d) None of the mentionedThis question was addressed to me during an online interview.My doubt stems from Public Key Cryptosystems topic in chapter Encryption and Decryption of Digital Communications

Answer»

The correct ANSWER is (a) ONE direction

To ELABORATE: A trapdoor is a one WAY function. Such FUNCTIONS can go easily in only one direction.
Discussion
44.

In public key cryptosystem _____ keys are used for encryption and decryption.(a) Same(b) Different(c) Encryption Keys(d) None of the mentionedThe question was posed to me during an interview for a job.Asked question is from Public Key Cryptosystems topic in division Encryption and Decryption of Digital Communications

Answer»

Right OPTION is (b) Different

The explanation is: In conventional cryptosystem, same keys are USED for ENCRYPTION and DECRYPTION where as in PUBLIC key cryptosystem different keys are used.
Discussion