CBCP Cryptography and Hashing 5 — Questions and Answers
Question 1: What is the role of the generator point G in elliptic curve cryptography as used in blockchain systems?
- It is a random value added to the private key for obfuscation
- It is a publicly known fixed point on the curve used to compute public keys via scalar multiplication (Correct answer)
- It is the hash of the curve parameters used for domain separation
- It represents the curve's order and sets the maximum private key value
Correct answer: It is a publicly known fixed point on the curve used to compute public keys via scalar multiplication
The generator point G is a standardized curve point; the public key is derived as k·G where k is the private key, and the discrete log problem makes reversing this infeasible.
Question 2: What does the term 'entropy' mean in the context of generating a blockchain private key or seed phrase?
- The computational energy required to mine a block
- A measure of randomness indicating how unpredictable the generated value is (Correct answer)
- The number of transactions a key can sign before expiration
- The compression ratio applied to the key before storage
Correct answer: A measure of randomness indicating how unpredictable the generated value is
Entropy quantifies the unpredictability of the random source; a 256-bit private key requires 256 bits of entropy from a cryptographically secure random number generator.
Question 3: Which BIP standard defines the mnemonic seed phrase (12–24 words) used to back up HD wallets?
- BIP-32
- BIP-39 (Correct answer)
- BIP-44
- BIP-141
Correct answer: BIP-39
BIP-39 specifies converting entropy into a human-readable mnemonic word list and then deriving a binary seed from those words via PBKDF2.
Question 4: How does a zero-knowledge proof allow one party to prove knowledge of a secret without revealing the secret itself?
- By encrypting the secret with the verifier's public key and sending the ciphertext
- By demonstrating possession of information through a mathematical protocol that reveals no additional details (Correct answer)
- By hashing the secret and publishing the hash for public verification
- By sharing a commitment key that both parties can use to decrypt the proof
Correct answer: By demonstrating possession of information through a mathematical protocol that reveals no additional details
Zero-knowledge proofs use mathematical protocols (e.g., zk-SNARKs, zk-STARKs) where a prover convinces a verifier of a statement's truth without exposing any underlying private data.
Question 5: In threshold cryptography, what does an (m, n) threshold signature scheme mean?
- n total signers must all sign; m is the minimum hash length required
- Any m out of n keyholders can jointly produce a valid signature, but fewer than m cannot (Correct answer)
- m is the number of rounds needed; n is the number of keys generated
- n signatures are needed in round one; m additional ones are needed in round two
Correct answer: Any m out of n keyholders can jointly produce a valid signature, but fewer than m cannot
An (m, n) threshold scheme distributes a private key across n parties such that any m of them can collaborate to sign, improving security by eliminating single points of failure.
Question 6: What is the primary security risk of reusing the same ECDSA nonce (k) for two different signatures with the same private key?
- The signature becomes invalid and is rejected by the network
- The private key can be mathematically extracted from the two signatures (Correct answer)
- The hash of the transaction becomes predictable to miners
- The public key is exposed in plaintext in the transaction
Correct answer: The private key can be mathematically extracted from the two signatures
If k is reused, an attacker with two signatures and the known nonce can solve for the private key algebraically using the ECDSA signature equations.
Question 7: Which construction does SHA-256 use to process arbitrarily long messages through fixed-size compression rounds?
- Sponge construction
- Feistel network
- Merkle-Damgård construction (Correct answer)
- Davies-Meyer construction only
Correct answer: Merkle-Damgård construction
SHA-256 uses the Merkle-Damgård construction, which pads the message, splits it into fixed-size blocks, and iteratively applies a compression function to produce the final hash.
CBCP Cryptography and Hashing 5
What is the role of the generator point G in elliptic curve cryptography as used in blockchain systems?