CBCP Cryptography and Security 5

Question 1

What is a 51% attack's relationship to cryptographic security in proof-of-work blockchains?

Accepted Answer

It overcomes cryptographic difficulty by controlling majority hash rate, enabling double-spend reorgs

Answer

A 51% attack doesn't break cryptography; it uses majority hash power to rewrite recent chain history, enabling double-spending by reversing confirmed transactions.

Question 2

Which post-quantum cryptographic algorithm family does NIST recommend as a primary standard for digital signatures?

Accepted Answer

CRYSTALS-Dilithium (lattice-based)

Answer

NIST standardized CRYSTALS-Dilithium (ML-DSA) as its primary post-quantum digital signature standard due to its strong security and performance.

Question 3

What is the purpose of key splitting using Shamir's Secret Sharing in blockchain custody?

Accepted Answer

To divide a private key into n shares such that any t shares reconstruct it, with fewer than t revealing nothing

Answer

Shamir's Secret Sharing splits a key into n shares with a t-of-n threshold; any t shares reconstruct the secret, but t-1 shares reveal zero information.

Question 4

In the context of blockchain smart contracts, what is a reentrancy attack and which cryptographic control prevents it?

Accepted Answer

An attack where a malicious contract recursively calls back before state updates; prevented by check-effects-interactions pattern and mutex locks

Answer

Reentrancy occurs when an external contract calls back into the vulnerable contract before its state is updated; the check-effects-interactions pattern and mutex locks prevent this.

Question 5

What is the difference between a public blockchain's transparency model and zero-knowledge proof-enhanced privacy?

Accepted Answer

Public blockchains expose all transaction data; ZKPs allow proving transaction validity without revealing the underlying data

Answer

Public chains are transparent by default; ZKPs (as in Zcash's zk-SNARKs) let nodes verify that rules are followed (balances don't go negative) without seeing amounts or addresses.

CBCP - Certified Blockchain Professional Practice Test

CBCP - Certified Blockchain Professional Practice Test

CBCP Cryptography and Security 5