CBSE Blockchain Cryptography Fundamentals 2 — Questions and Answers
Question 1: Which property of a cryptographic hash function ensures that finding two different inputs that produce the same hash output is computationally infeasible?
- Pre-image resistance
- Second pre-image resistance
- Collision resistance (Correct answer)
- Avalanche effect
Correct answer: Collision resistance
Collision resistance means it is computationally infeasible to find two distinct inputs x and y such that H(x) = H(y).
Question 2: In elliptic curve cryptography (ECC), the security relies on the hardness of which mathematical problem?
- Integer factorization problem
- Discrete logarithm problem on elliptic curves (Correct answer)
- Quadratic residuosity problem
- Subset sum problem
Correct answer: Discrete logarithm problem on elliptic curves
ECC security is based on the elliptic curve discrete logarithm problem (ECDLP), which is harder than the standard discrete log problem for the same key size.
Question 3: A blockchain uses SHA-256 to hash block headers. An attacker wants to find an input that hashes to a specific target value. Which property prevents this?
- Collision resistance
- Second pre-image resistance
- Pre-image resistance (Correct answer)
- Determinism
Correct answer: Pre-image resistance
Pre-image resistance ensures that given a hash output H(x), it is computationally infeasible to find any input x that produces that output.
Question 4: Which of the following best describes a Merkle tree in blockchain?
- A linked list of transaction IDs
- A binary tree where each non-leaf node is the hash of its children (Correct answer)
- A symmetric encryption scheme for transaction data
- A zero-knowledge proof structure for private transactions
Correct answer: A binary tree where each non-leaf node is the hash of its children
A Merkle tree is a binary hash tree where each leaf is a transaction hash and each parent node is the hash of its two children, enabling efficient verification.
Question 5: What is the key advantage of using ECDSA over RSA for digital signatures in blockchain systems?
- ECDSA supports symmetric encryption natively
- ECDSA provides equivalent security with significantly smaller key sizes (Correct answer)
- ECDSA uses prime factorization for faster verification
- ECDSA does not require a random number generator
Correct answer: ECDSA provides equivalent security with significantly smaller key sizes
ECDSA achieves equivalent cryptographic security to RSA but with much smaller keys (e.g., 256-bit ECC ≈ 3072-bit RSA), reducing storage and bandwidth overhead.
Question 6: In ECDSA signature generation, reusing the same nonce k for two different messages with the same private key results in:
- A stronger signature that is harder to forge
- Exposure of the private key to any observer (Correct answer)
- An invalid signature that the network rejects
- A collision in the hash of the signed message
Correct answer: Exposure of the private key to any observer
If the same nonce k is used to sign two different messages, an attacker can solve for the private key algebraically using the two signature equations.
Question 7: Which cryptographic primitive is used in Bitcoin's Proof-of-Work to create a target-meeting hash?
- HMAC-SHA256
- SHA-256 applied twice (SHA-256d) (Correct answer)
- Keccak-256
- RIPEMD-160
Correct answer: SHA-256 applied twice (SHA-256d)
Bitcoin's Proof-of-Work uses double SHA-256 (SHA-256 of SHA-256) on the block header to produce a hash that must be below the network difficulty target.
CBSE Blockchain Cryptography Fundamentals 2
Which property of a cryptographic hash function ensures that finding two different inputs that produce the same hash output is computationally infeasible?