CBSA Blockchain Security and Privacy 2 — Questions and Answers
Question 1: Which cryptographic technique allows a prover to convince a verifier that a statement is true without revealing any information beyond the validity of the statement?
- Homomorphic encryption
- Zero-knowledge proof (Correct answer)
- Threshold signature
- Ring signature
Correct answer: Zero-knowledge proof
Zero-knowledge proofs (ZKPs) let a prover demonstrate knowledge of a secret without disclosing the secret itself, enabling privacy-preserving verification on blockchains.
Question 2: In a Hyperledger Fabric network, what mechanism restricts which peers can see specific transaction data?
- Orderer filtering
- Private data collections (Correct answer)
- BYFN consensus
- Endorsement policy
Correct answer: Private data collections
Private data collections in Hyperledger Fabric allow only authorized peers to access the actual data while the hash of the data is recorded on the main ledger.
Question 3: An attacker intercepts a signed blockchain transaction and replays it on a different chain with the same chain parameters. Which protection prevents this?
- Nonce enforcement
- Chain ID in transaction signing (EIP-155) (Correct answer)
- Merkle proofs
- ECDSA key rotation
Correct answer: Chain ID in transaction signing (EIP-155)
EIP-155 includes the chain ID in the transaction signature so a transaction signed for one network is cryptographically invalid on any other network.
Question 4: Which consensus attack requires an adversary to control more than 50% of a proof-of-work network's hash rate?
- Sybil attack
- Eclipse attack
- 51% attack (Correct answer)
- Nothing-at-stake attack
Correct answer: 51% attack
A 51% attack gives the majority miner the ability to reorganize the blockchain, reverse transactions, and double-spend by outpacing honest miners.
Question 5: What is the primary security risk of using a deterministic wallet (BIP-32/BIP-44) without proper key management?
- Collision in address generation
- Compromise of the master seed exposes all derived keys (Correct answer)
- Inability to sign multi-sig transactions
- Incompatibility with hardware wallets
Correct answer: Compromise of the master seed exposes all derived keys
Because all child keys are deterministically derived from the master seed, an attacker who obtains the seed can regenerate every private key in the wallet hierarchy.
Question 6: In a permissioned blockchain, which identity management model uses X.509 certificates issued by a Certificate Authority to authenticate participants?
- Self-sovereign identity (SSI)
- Membership Service Provider (MSP) (Correct answer)
- Decentralized identifiers (DID)
- OAuth 2.0 federation
Correct answer: Membership Service Provider (MSP)
Hyperledger Fabric's Membership Service Provider uses X.509 certificates from a CA to define and verify the identities of all network participants.
Question 7: A smart contract stores sensitive patient records directly on a public blockchain. What is the most critical privacy violation this causes?
- Gas cost increases
- Data immutability makes personal data erasure impossible, violating GDPR (Correct answer)
- Miners can alter the records
- Oracles cannot read the data
Correct answer: Data immutability makes personal data erasure impossible, violating GDPR
Immutable public blockchains conflict with the GDPR 'right to be forgotten' because personal data stored on-chain cannot be deleted once confirmed.
CBSA Blockchain Security and Privacy 2
Which cryptographic technique allows a prover to convince a verifier that a statement is true without revealing any information beyond the validity of the statement?