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Cryptography

Topic in Cyber Security

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About This Topic

Cryptography is the study of techniques that secure information by turning plaintext into ciphertext so only authorized parties can read or verify it. Questions start with terminology (cipher, key, plaintext, ciphertext) and classical ciphers such as Caesar, Vigenère and the one-time pad. Symmetric algorithms like DES, 3DES and AES, with block cipher modes such as ECB and CBC, are contrasted with asymmetric schemes such as RSA, Diffie-Hellman and elliptic-curve cryptography. Hash functions like MD5 and SHA-256 and their collision resistance, MACs and HMAC, digital signatures, certificates and PKI complete the picture, along with why hashing differs from encryption.

Below are 30 practice questions from a pool of 240 Cryptography MCQs, one of 16 topics in Cyber Security. Each shows the correct answer with an explanation; when you are ready, take a timed quiz to test recall under exam conditions.

Practice Questions

Each question below shows the correct answer with a full explanation. Use these to build conceptual understanding before attempting a timed quiz.

CryptographyEasy

Q1. What is cryptography?

  1. A.Study of databases within enterprise security environments
  2. B.Study of networks within enterprise security environments
  3. C.Study of computers within enterprise security environments
  4. D.The practice of securing communication through encoding messages✓ Correct

Explanation

Cryptography is the science of securing communication and data through encoding.

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CryptographyEasy

Q2. What is ciphertext?

  1. A.A hash function within modern computing environments
  2. B.A type of key within modern computing environments
  3. C.A readable message within modern computing environments
  4. D.The encrypted, unreadable form of a message✓ Correct

Explanation

Ciphertext is the scrambled, unreadable output produced by encrypting plaintext.

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CryptographyEasy

Q3. What is a cryptographic key?

  1. A.A physical metal key for a locked server room
  2. B.A piece of information used to encrypt and decrypt data✓ Correct
  3. C.A strain of self-replicating malicious software programs
  4. D.A physical cable used for network connections

Explanation

A cryptographic key is a string of bits used by a cryptographic algorithm to transform plaintext into ciphertext and vice versa.

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CryptographyEasy

Q4. What is plaintext in cryptography?

  1. A.The original readable message before encryption✓ Correct
  2. B.A cryptographic key applied to data protection workflows
  3. C.A type of cipher applied to data protection workflows
  4. D.Encrypted data within enterprise security environments

Explanation

Plaintext is the original, readable data or message before it undergoes encryption.

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CryptographyEasy

Q5. Which of the following is a symmetric encryption algorithm?

  1. A.RSA
  2. B.ECC
  3. C.Diffie-Hellman
  4. D.AES✓ Correct

Explanation

AES (Advanced Encryption Standard) is a symmetric encryption algorithm that uses the same key for both encryption and decryption.

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CryptographyEasy

Q6. What is the Caesar cipher?

  1. A.An asymmetric algorithm within modern computing environments
  2. B.A hash function within modern computing environments
  3. C.A modern encryption standard applied to data protection workflows
  4. D.A simple substitution cipher that shifts letters by a fixed number✓ Correct

Explanation

The Caesar cipher is one of the simplest encryption techniques, where each letter is shifted by a fixed number of positions.

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CryptographyEasy

Q7. What is the purpose of a digital signature?

  1. A.To compress files for reducing disk storage consumption
  2. B.To sign documents physically within enterprise computing infrastructure
  3. C.To verify the authenticity and integrity of a digital message✓ Correct
  4. D.To encrypt all data using established cryptographic standards

Explanation

A digital signature uses cryptographic techniques to verify that a message was created by a known sender and has not been altered.

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CryptographyEasy

Q8. What is decryption?

  1. A.Converting plaintext to ciphertext
  2. B.Converting ciphertext back to plaintext✓ Correct
  3. C.Compressing data files for reduced storage space consumption
  4. D.Deleting encrypted data in security contexts

Explanation

Decryption is the reverse process of encryption, converting ciphertext back to its original plaintext using a key.

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CryptographyMedium

Q9. What is the key size of AES-256?

  1. A.256 bits✓ Correct
  2. B.192 bits
  3. C.512 bits
  4. D.128 bits

Explanation

AES-256 uses a 256-bit key length, providing a very high level of security.

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CryptographyMedium

Q10. What is a stream cipher?

  1. A.A cipher that encrypts entire files at once
  2. B.A cipher that encrypts data one bit or byte at a time✓ Correct
  3. C.A cipher that uses block processing
  4. D.A cipher that only works with video

Explanation

A stream cipher encrypts plaintext one bit or byte at a time, typically by XORing with a pseudorandom keystream.

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CryptographyEasy

Q11. Which of the following is an asymmetric encryption algorithm?

  1. A.Blowfish
  2. B.DES
  3. C.RSA✓ Correct
  4. D.AES

Explanation

RSA is an asymmetric encryption algorithm that uses a public key for encryption and a private key for decryption.

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CryptographyMedium

Q12. What is a block cipher?

  1. A.A cipher that encrypts one bit at a time
  2. B.A cryptographic algorithm used for protecting sensitive data
  3. C.A cipher that encrypts fixed-size blocks of data at a time✓ Correct
  4. D.A cipher that uses no key applied to data protection workflows

Explanation

A block cipher encrypts data in fixed-size blocks (e.g., 128 bits for AES).

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CryptographyEasy

Q13. What is a public key in asymmetric cryptography?

  1. A.A key that is freely shared and used for encrypting messages✓ Correct
  2. B.A key that must be kept secret used in enterprise computing environments
  3. C.A password within the identity management system
  4. D.A physical key within modern computing environments

Explanation

In asymmetric cryptography, the public key is shared openly and used to encrypt messages that only the corresponding private key can decrypt.

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CryptographyMedium

Q14. What is a digital certificate?

  1. A.A cryptographic algorithm used for protecting sensitive data
  2. B.An electronic document that uses a digital signature to bind a public key with an identity✓ Correct
  3. C.A software application used for enterprise computing operations
  4. D.A physical security measure for protecting building infrastructure

Explanation

A digital certificate is an electronic credential issued by a Certificate Authority that binds a public key to an identity.

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CryptographyMedium

Q15. What is the role of a Certificate Authority (CA)?

  1. A.To design websites for enterprise computing environments
  2. B.To develop software across enterprise computing systems
  3. C.To design and distribute malicious software programs
  4. D.To issue, manage, and revoke digital certificates✓ Correct

Explanation

A Certificate Authority is a trusted entity that issues digital certificates, verifying the identity of certificate holders.

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CryptographyHard

Q16. What is elliptic curve cryptography (ECC)?

  1. A.A data compression technique that reduces file sizes within enterprise computing environments
  2. B.A cryptographic hashing algorithm used within enterprise computing environments for integrity
  3. C.A symmetric block cipher algorithm widely used for protecting sensitive data at rest
  4. D.An asymmetric approach using elliptic curves over finite fields for smaller key sizes with equivalent security✓ Correct

Explanation

ECC uses elliptic curves over finite fields, providing equivalent security to RSA with significantly smaller key sizes.

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CryptographyMedium

Q17. Which hash algorithm produces a 256-bit output?

  1. A.SHA-256✓ Correct
  2. B.SHA-512
  3. C.MD5
  4. D.SHA-1

Explanation

SHA-256 produces a 256-bit (32-byte) hash value and is widely used for data integrity verification.

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CryptographyMedium

Q18. Why is MD5 considered insecure for cryptographic purposes?

  1. A.It requires too much memory within enterprise security environments
  2. B.It is too slow within enterprise security environments
  3. C.It is vulnerable to collision attacks where two different inputs produce the same hash✓ Correct
  4. D.It produces too long an output within enterprise security environments

Explanation

MD5 is cryptographically broken because practical collision attacks have been demonstrated.

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CryptographyHard

Q19. What is an Initialization Vector (IV) in block cipher modes?

  1. A.A type of hash function within modern computing environments
  2. B.A random value used with a key to ensure identical plaintexts produce different ciphertexts✓ Correct
  3. C.The first encryption key within enterprise security environments
  4. D.A decryption algorithm within enterprise computing environments

Explanation

An IV is a random value used alongside the key in block cipher modes like CBC to ensure identical plaintext blocks encrypt to different ciphertext blocks.

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CryptographyMedium

Q20. What is the purpose of a nonce in cryptography?

  1. A.A number used only once to prevent replay attacks✓ Correct
  2. B.To compress files for reducing disk storage consumption
  3. C.To create automated backup copies of user data
  4. D.To encrypt data using symmetric cipher algorithms

Explanation

A nonce (number used once) is an arbitrary number used only once in cryptographic communication to prevent replay attacks.

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CryptographyHard

Q21. What mathematical problem does RSA encryption rely on?

  1. A.The traveling salesman optimization problem
  2. B.The difficulty of factoring large prime numbers✓ Correct
  3. C.The discrete logarithm mathematical problem
  4. D.Elliptic curve mathematical computation

Explanation

RSA security relies on the computational difficulty of factoring the product of two large prime numbers.

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CryptographyMedium

Q22. What is the Diffie-Hellman key exchange used for?

  1. A.Hashing passwords within enterprise security environments
  2. B.Compressing data files for reduced storage space consumption
  3. C.Encrypting data directly within enterprise security environments
  4. D.Securely exchanging cryptographic keys over an insecure channel✓ Correct

Explanation

Diffie-Hellman allows two parties to securely establish a shared secret key over an insecure communication channel.

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CryptographyMedium

Q23. What is PKI (Public Key Infrastructure)?

  1. A.A next-generation firewall for filtering network traffic flows
  2. B.A framework for managing digital certificates and public-key encryption✓ Correct
  3. C.A category of self-replicating malicious software
  4. D.A standard network communication protocol for data transfer

Explanation

PKI is a set of roles, policies, hardware, software, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates.

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CryptographyHard

Q24. Which block cipher mode is considered insecure for encrypting multiple blocks?

  1. A.CBC (Cipher Block Chaining)
  2. B.ECB (Electronic Codebook)✓ Correct
  3. C.GCM (Galois/Counter Mode)
  4. D.CTR (Counter) in security contexts

Explanation

ECB mode encrypts each block independently, causing identical plaintext blocks to produce identical ciphertext blocks, revealing patterns.

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CryptographyHard

Q25. What is a man-in-the-middle attack on key exchange?

  1. A.A brute force attack targeting enterprise network infrastructure used in enterprise computing environments
  2. B.A dictionary attack targeting enterprise network infrastructure used in enterprise computing environments
  3. C.An attacker intercepting and altering communication between two parties who believe they are communicating directly✓ Correct
  4. D.Physically stealing keys within enterprise security environments

Explanation

In a MITM attack on key exchange, an attacker intercepts the process and establishes separate keys with each party.

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CryptographyHard

Q26. What is perfect forward secrecy (PFS)?

  1. A.Using only symmetric encryption without any additional considerations needed
  2. B.Using the same key forever with no meaningful distinction between them
  3. C.Never changing encryption keys in any deployment scenario or context
  4. D.A property ensuring that compromise of long-term keys does not compromise past session keys✓ Correct

Explanation

PFS ensures that even if a long-term secret key is compromised, previously recorded encrypted sessions remain secure.

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CryptographyHard

Q27. Which is a post-quantum cryptographic approach?

  1. A.Lattice-based cryptography✓ Correct
  2. B.AES-128 symmetric block cipher
  3. C.SHA-256 cryptographic hashing
  4. D.RSA-2048 key exchange scheme

Explanation

Lattice-based cryptography is a leading candidate for post-quantum cryptography, believed to be resistant to quantum computer attacks.

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CryptographyHard

Q28. What is the purpose of HMAC?

  1. A.To reduce data sizes through compression methods and management
  2. B.To verify both data integrity and authenticity using a hash function and secret key✓ Correct
  3. C.To encrypt messages using established cryptographic standards
  4. D.To generate random numbers within enterprise computing infrastructure

Explanation

HMAC combines a cryptographic hash function with a secret key to provide both data integrity verification and message authentication.

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CryptographyHard

Q29. What is the purpose of key stretching algorithms like PBKDF2 and bcrypt?

  1. A.To speed up encryption using established cryptographic standards
  2. B.To compress encryption keys using established cryptographic standards
  3. C.To make brute-force attacks on passwords computationally expensive by adding iterations✓ Correct
  4. D.To make keys shorter within enterprise computing infrastructure

Explanation

Key stretching algorithms deliberately slow down hashing by applying the function many times, making brute-force attacks impractical.

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CryptographyHard

Q30. What is homomorphic encryption?

  1. A.Encryption that only works on text without any additional considerations needed
  2. B.A method to compress encrypted data for managing enterprise data resources
  3. C.Encryption that allows computations on ciphertext without decrypting it first✓ Correct
  4. D.A type of symmetric encryption applied to data protection workflows

Explanation

Homomorphic encryption enables computation on encrypted data without decrypting it, producing encrypted results matching operations on plaintext.

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