B.The practice and study of techniques for secure communication in the presence of third parties
C.The process of converting hardware signals into software
D.The database management of blockchain nodes
Correct Answer: The practice and study of techniques for secure communication in the presence of third parties
Explanation:Cryptography is derived from the Greek words 'kryptos' (hidden) and 'graphein' (to write). It involves constructing and analyzing protocols that prevent third parties or the public from reading private messages.
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2In the context of cryptography, what does Plaintext refer to?
A.The encrypted data
B.The original unencrypted input data
C.The secret key used for encryption
D.The mathematical algorithm used
Correct Answer: The original unencrypted input data
Explanation:Plaintext is the input to an encryption algorithm, such as a readable message or raw data, before it is transformed into ciphertext.
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3Which principle states that a cryptosystem should be secure even if everything about the system, except the key, is public knowledge?
A.Moore's Law
B.Kerckhoffs's Principle
C.Shannon's Theorem
D.Bernoulli's Principle
Correct Answer: Kerckhoffs's Principle
Explanation:Kerckhoffs's principle implies that security should depend solely on the secrecy of the key, not the secrecy of the algorithm (security by obscurity is discouraged).
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4Which of the following best describes Symmetric Cryptography?
A.Sender and receiver use different keys
B.Sender uses a public key and receiver uses a private key
C.Sender and receiver share a single, common secret key
D.No keys are required for communication
Correct Answer: Sender and receiver share a single, common secret key
Explanation:In symmetric cryptography, the same key is used for both encryption and decryption. Both parties must possess this shared secret.
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5If there are users in a network using Symmetric Cryptography, how many total keys are required for every pair of users to communicate securely?
A.
B.
C.
D.
Correct Answer:
Explanation:This is the key distribution problem in symmetric encryption. For users, the number of distinct pairs is , requiring that many unique keys.
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6Which of the following is a classic example of a Symmetric Encryption algorithm?
Explanation:AES is a symmetric block cipher established by NIST. RSA, ECC, and Diffie-Hellman are asymmetric algorithms.
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7What is the primary advantage of Symmetric Cryptography over Asymmetric Cryptography?
A.Easier key distribution
B.Provides non-repudiation natively
C.Faster computation speed
D.Supports digital signatures directly
Correct Answer: Faster computation speed
Explanation:Symmetric algorithms (like AES) are significantly faster and require less computational power than asymmetric algorithms (like RSA), making them suitable for encrypting large amounts of data.
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8In Asymmetric Cryptography, which key is used to encrypt a message intended for Bob?
A.Bob's Private Key
B.Bob's Public Key
C.The Sender's Private Key
D.The Sender's Public Key
Correct Answer: Bob's Public Key
Explanation:To ensure confidentiality, the sender encrypts the message using the recipient's (Bob's) Public Key. Only Bob can decrypt it using his corresponding Private Key.
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9What is the mathematical relationship between the Public Key () and Private Key () in a secure asymmetric system?
A.They are identical ()
B.It is computationally infeasible to derive from
C. is the inverse of divided by 2
D.They are unrelated random numbers
Correct Answer: It is computationally infeasible to derive from
Explanation:While the keys are mathematically related (e.g., via prime factorization in RSA or discrete logs in ECC), the system relies on the 'one-way' nature where calculating the private key from the public key is practically impossible.
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10Which cryptographic primitive is primarily used to verify the integrity of data in a Blockchain?
A.Stream Cipher
B.Cryptographic Hash Function
C.Key Exchange Protocol
D.Symmetric Decryption
Correct Answer: Cryptographic Hash Function
Explanation:Hash functions generate a unique fixed-size string (digest) from input data. Any change in the input data results in a completely different hash, allowing for integrity verification.
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11What is the Avalanche Effect in hashing?
A.A small change in input results in a drastic change in the output hash
B.The hash function gets slower as more data is processed
C.The output size grows as the input size grows
D.Collisions become more frequent over time
Correct Answer: A small change in input results in a drastic change in the output hash
Explanation:A desirable property of cryptographic hash functions is that flipping a single bit in the input should change approximately 50% of the bits in the output hash.
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12Which property of a hash function ensures that it is infeasible to find an input such that given a specific hash output ?
A.Collision Resistance
B.Pre-image Resistance
C.Second Pre-image Resistance
D.Determinism
Correct Answer: Pre-image Resistance
Explanation:Pre-image resistance (or one-wayness) means that given a hash value, it is computationally hard to reverse the function to find the original input message.
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13What is a Hash Collision?
A.When two different inputs produce the same hash output
B.When the hash function fails to produce an output
C.When the private key is lost
D.When encryption overwrites data
Correct Answer: When two different inputs produce the same hash output
Explanation:A collision occurs when distinct inputs and () result in . Good hash functions make finding collisions extremely difficult.
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14Which hash function family is predominantly used in Bitcoin?
A.MD5
B.SHA-1
C.SHA-256
D.Keccak-256
Correct Answer: SHA-256
Explanation:Bitcoin uses SHA-256 (Secure Hash Algorithm 256-bit) for Proof-of-Work mining and creating addresses.
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15What is the output length of the SHA-256 algorithm?
A.128 bits
B.256 bytes
C.256 bits
D.512 bits
Correct Answer: 256 bits
Explanation:SHA-256 always produces a fixed output (digest) of 256 bits (32 bytes), regardless of the input size.
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16Which cryptographic primitive allows a user to prove they know a private key without revealing it, thereby providing Non-Repudiation?
A.AES Encryption
B.Digital Signature
C.Hashing
D.Salted Hash
Correct Answer: Digital Signature
Explanation:Digital signatures use asymmetric cryptography. A user signs data with their private key. Others verify it with the public key. This proves origin and prevents the signer from denying the action (non-repudiation).
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17In a Digital Signature scheme, which key is used to create the signature?
A.Receiver's Public Key
B.Receiver's Private Key
C.Sender's Public Key
D.Sender's Private Key
Correct Answer: Sender's Private Key
Explanation:To sign a message, the sender uses their own Private Key. The signature can later be verified by anyone using the sender's Public Key.
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18What does RSA stand for?
A.Random Security Algorithm
B.Rivest-Shamir-Adleman
C.Real Secure Access
D.Recursive System Architecture
Correct Answer: Rivest-Shamir-Adleman
Explanation:RSA is named after its inventors: Ron Rivest, Adi Shamir, and Leonard Adleman.
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19The security of RSA is based on the computational difficulty of which mathematical problem?
A.Discrete Logarithm Problem
B.Elliptic Curve Discrete Logarithm Problem
C.Integer Factorization of large prime products
D.Knapsack Problem
Correct Answer: Integer Factorization of large prime products
Explanation:RSA relies on the fact that multiplying two large primes is easy, but factoring the resulting product back into the primes is computationally infeasible.
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20What is ECC in the context of cryptography?
A.Error Correcting Code
B.Elliptic Curve Cryptography
C.Encrypted Cipher Chain
D.Electronic Code Cipher
Correct Answer: Elliptic Curve Cryptography
Explanation:Elliptic Curve Cryptography is an approach to public-key cryptography based on the algebraic structure of elliptic curves over finite fields.
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21Why is ECC preferred over RSA in many modern blockchain systems?
A.ECC is symmetric
B.ECC provides the same security level with much smaller key sizes
C.ECC does not require mathematics
D.ECC is older and more tested than RSA
Correct Answer: ECC provides the same security level with much smaller key sizes
Explanation:ECC is more efficient. For example, a 256-bit ECC key offers comparable security to a 3072-bit RSA key, saving storage and bandwidth.
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22Which of the following describes a Block Cipher?
A.Encrypts data one bit or byte at a time continuously
B.Encrypts data in fixed-size chunks (e.g., 64 or 128 bits)
C.Does not use a key
D.Uses a physical pad for encryption
Correct Answer: Encrypts data in fixed-size chunks (e.g., 64 or 128 bits)
Explanation:A block cipher (like AES) breaks the plaintext into fixed-size blocks and encrypts each block, as opposed to a stream cipher which encrypts a continuous stream.
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23What is the purpose of a Nonce in cryptography and blockchain mining?
A.It is the private key
B.It is a number used only once to vary the hash output
C.It is the name of the encryption algorithm
D.It is the block size limit
Correct Answer: It is a number used only once to vary the hash output
Explanation:In Proof of Work, a Nonce (Number used ONCE) is an arbitrary number that miners change to attempt to generate a hash that meets the difficulty target.
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24What is Diffie-Hellman used for?
A.Digital Signatures
B.Hashing data
C.Secure Key Exchange over an insecure channel
D.File compression
Correct Answer: Secure Key Exchange over an insecure channel
Explanation:The Diffie-Hellman protocol allows two parties to establish a shared secret key over an insecure communication channel without having shared a secret beforehand.
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25Which of the following is a property of a Deterministic system?
A.Same input always produces the same output
B.Same input produces different outputs every time
C.Output cannot be predicted
D.Output depends on the time of day
Correct Answer: Same input always produces the same output
Explanation:In cryptography (specifically hashing and signatures), determinism ensures that processing the exact same data with the same parameters yields the exact same result.
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26The CIA Triad in information security stands for:
Explanation:These are the three core goals of information security. Cryptography heavily supports Confidentiality and Integrity.
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27What is the Discrete Logarithm Problem?
A.Given and , it is hard to find
B.Given and , it is hard to find
C.It is hard to multiply two numbers
D.It is hard to sort a list of logs
Correct Answer: Given and , it is hard to find
Explanation:In modular arithmetic, computing is easy, but finding given is computationally hard. This underpins Diffie-Hellman and ElGamal.
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28Which attack aims to find a collision in a hash function by checking random inputs, often approximated by the Birthday Paradox?
A.Brute Force Attack
B.Birthday Attack
C.Man-in-the-Middle Attack
D.Replay Attack
Correct Answer: Birthday Attack
Explanation:The Birthday Attack exploits the mathematics of probability (Birthday Paradox) to find collisions in hash functions faster than a standard brute force search.
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29In the context of Block Ciphers, what does ECB stand for?
A.Electronic Code Book
B.Encrypted Cipher Block
C.Elliptic Curve Basis
D.Extended Code Base
Correct Answer: Electronic Code Book
Explanation:Electronic Code Book (ECB) is the simplest mode of operation where identical plaintext blocks are encrypted into identical ciphertext blocks (generally considered insecure for large data).
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30Which cryptographic concept ensures that a sender cannot deny having sent a message?
A.Confidentiality
B.Non-repudiation
C.Availability
D.Obfuscation
Correct Answer: Non-repudiation
Explanation:Non-repudiation is typically achieved via Digital Signatures, preventing the signer from claiming they did not sign the message.
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31What is Salting in the context of password hashing?
A.Adding random data to the input before hashing
B.Encrypting the hash twice
C.Using two different hash algorithms
D.Shortening the hash output
Correct Answer: Adding random data to the input before hashing
Explanation:A salt is random data added to a password before hashing to defend against dictionary attacks and rainbow table attacks.
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32Which of the following is NOT a property of a cryptographic hash function?
A.Variable output size
B.Pre-image resistance
C.Collision resistance
D.Computationally efficient
Correct Answer: Variable output size
Explanation:Cryptographic hash functions must have a fixed output size (e.g., 256 bits), regardless of input size.
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33In Elliptic Curve Cryptography, the equation is typically of the form:
A.
B.
C.
D.
Correct Answer:
Explanation:This is the Weierstrass form of an elliptic curve used in cryptography over finite fields.
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34What is the role of a Certificate Authority (CA) in PKI (Public Key Infrastructure)?
A.To store private keys
B.To issue and verify digital certificates linking public keys to identities
C.To mine blocks in a blockchain
D.To provide internet connection
Correct Answer: To issue and verify digital certificates linking public keys to identities
Explanation:A CA acts as a trusted third party that validates identities and issues certificates, ensuring a specific public key belongs to a specific entity.
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35Which algorithm is a Stream Cipher?
A.AES
B.DES
C.RC4
D.RSA
Correct Answer: RC4
Explanation:RC4 is a well-known stream cipher that processes data byte-by-byte, whereas AES and DES are block ciphers.
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36What constitutes a Key Pair in blockchain wallets?
A.A username and password
B.A Private Key and a Public Key
C.Two Private Keys
D.A Hash and a Salt
Correct Answer: A Private Key and a Public Key
Explanation:Blockchain wallets rely on asymmetric cryptography, generating a mathematically linked Private Key (for spending/signing) and Public Key (for receiving/verifying).
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37Why is MD5 no longer recommended for cryptographic security?
A.It is too slow
B.It produces outputs that are too long
C.It has severe collision vulnerabilities
D.It requires a paid license
Correct Answer: It has severe collision vulnerabilities
Explanation:Researchers have demonstrated practical collision attacks against MD5, allowing two different files to have the same hash, rendering it insecure for signatures or integrity checks.
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38In the equation , what does represent?
A.Ciphertext
B.Key
C.Plaintext
D.Encryption Function
Correct Answer: Key
Explanation:In cryptographic notation, represents the Key used by the Encryption function () to transform Plaintext () into Ciphertext ().
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39What is the key size of DES (Data Encryption Standard)?
A.56 bits
B.128 bits
C.256 bits
D.512 bits
Correct Answer: 56 bits
Explanation:DES uses a 56-bit effective key size (64 bits with parity bits), which is now considered too short and vulnerable to brute-force attacks.
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40Which cryptographic primitive is used to link blocks together in a Blockchain?
A.RSA Encryption
B.Hash Pointers
C.Symmetric Keys
D.Stream Ciphers
Correct Answer: Hash Pointers
Explanation:A block contains the hash of the previous block header. This creates a chain where changing any historical block would invalidate the hashes of all subsequent blocks.
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41What is ECDSA?
A.Elliptic Curve Digital Signature Algorithm
B.Encrypted Code Data System Access
C.Electronic Cipher Digital Standard Algorithm
D.Extended Curve Data Security Act
Correct Answer: Elliptic Curve Digital Signature Algorithm
Explanation:ECDSA is the specific implementation of Digital Signatures using Elliptic Curve Cryptography, used in Bitcoin and Ethereum.
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42If User A encrypts a message with User B's Public Key, who can decrypt it?
A.User A
B.User B
C.Both User A and User B
D.Anyone with User A's Public Key
Correct Answer: User B
Explanation:In asymmetric encryption, data encrypted with a Public Key can ONLY be decrypted by the corresponding Private Key, which only User B possesses.
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43What is a Merkle Tree?
A.A database of user keys
B.A binary tree of hashes used to efficiently summarize and verify data integrity
C.A type of encryption algorithm
D.A method for generating random numbers
Correct Answer: A binary tree of hashes used to efficiently summarize and verify data integrity
Explanation:A Merkle Tree hashes transactions in pairs until a single Root Hash is obtained, allowing efficient verification of whether a transaction exists in a block.
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44Which of the following is considered Quantum-Resistant?
A.RSA-2048
B.ECC-256
C.Lattice-based Cryptography
D.Diffie-Hellman
Correct Answer: Lattice-based Cryptography
Explanation:Standard RSA and ECC are vulnerable to Shor's algorithm on quantum computers. Lattice-based cryptography is a leading candidate for post-quantum security.
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45What is the difference between a Weak Collision and a Strong Collision resistance?
A.Weak is for passwords, Strong is for blockchain
B.Weak relates to pre-image resistance; Strong relates to finding ANY pair of colliding inputs
C.Weak protects the public key; Strong protects the private key
D.There is no difference
Correct Answer: Weak relates to pre-image resistance; Strong relates to finding ANY pair of colliding inputs
Explanation:Weak collision resistance (Second pre-image) means given , it's hard to find such that . Strong collision resistance means it's hard to find any pair such that .
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46In a symmetric cipher, if the key is intercepted by an attacker, what is compromised?
A.Only future messages
B.Only past messages
C.Both past and future messages
D.Nothing, unless they have the algorithm
Correct Answer: Both past and future messages
Explanation:Since the same key is used for encryption and decryption, possession of the key allows an attacker to decrypt previously captured traffic and any future traffic.
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47What is the function of a Trapdoor Function in cryptography?
A.It deletes data automatically
B.It is easy to compute in one direction, but hard to reverse without special information (the trapdoor)
C.It allows unauthorized access to the system
D.It generates random keys
Correct Answer: It is easy to compute in one direction, but hard to reverse without special information (the trapdoor)
Explanation:Asymmetric cryptography relies on trapdoor one-way functions. For example, multiplication is easy, factorization is hard, but factorization becomes easy if you know one of the prime factors (the trapdoor).
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48Which of the following describes Triple DES (3DES)?
A.Applying DES three times with up to three different keys
B.A completely new algorithm unrelated to DES
C.DES with a 3-bit key
D.Encrypting three blocks at once
Correct Answer: Applying DES three times with up to three different keys
Explanation:To fix the short key length of DES, 3DES runs the DES algorithm three times (Encrypt-Decrypt-Encrypt) to increase effective security, though it is now being replaced by AES.