CBSE Blockchain Cryptography Fundamentals 5

Question 1

Which of the following post-quantum cryptographic algorithm families is a NIST-standardized candidate primarily used for key encapsulation and digital signatures?

Accepted Answer

Lattice-based cryptography (e.g., CRYSTALS-Kyber, CRYSTALS-Dilithium)

Answer

NIST standardized lattice-based algorithms CRYSTALS-Kyber (key encapsulation) and CRYSTALS-Dilithium (signatures) as post-quantum replacements resistant to Shor's algorithm.

Question 2

Grover's quantum algorithm poses a threat to symmetric cryptography by reducing the effective security of an n-bit key to approximately:

Accepted Answer

n/2 bits

Answer

Grover's algorithm provides a quadratic speedup for brute-force search, effectively halving the bit security of symmetric keys, so AES-256 retains ~128 bits of quantum security.

Question 3

In the context of smart contract security, which cryptographic function does Solidity's `ecrecover` perform?

Accepted Answer

Recovers the Ethereum address (public key) from a message hash and ECDSA signature

Answer

ecrecover takes a hashed message and an ECDSA signature (v, r, s) and returns the Ethereum address of the signer, enabling on-chain signature verification.

Question 4

A timing side-channel attack against a cryptographic implementation exploits:

Accepted Answer

Variations in execution time that leak information about secret values

Answer

Timing attacks measure how long cryptographic operations take; non-constant-time implementations can leak secret key bits through measurable timing differences.

Question 5

What is a stealth address in privacy-focused blockchains, and which cryptographic operation is it based on?

Accepted Answer

A one-time address per transaction derived via Diffie-Hellman key exchange between sender and recipient

Answer

Stealth addresses use ECDH between the sender's ephemeral key and the recipient's public key to generate a one-time address per transaction, unlinkable to the recipient's public identity.

(CBSE) Certified Blockchain Security Expert Practice Test

(CBSE) Certified Blockchain Security Expert Practice Test

CBSE Blockchain Cryptography Fundamentals 5