Cryptography and Security Flashcards

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

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

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

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

Answer: CRYSTALS-Dilithium (lattice-based)

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

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

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

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.

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

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

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.

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

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

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.

What is a cryptographic accumulator and how is it used in blockchain scalability?

Answer: A data structure that proves set membership without revealing the full set, used in stateless clients and rollups

Cryptographic accumulators (e.g., RSA or Merkle-based) allow compact proofs of membership or non-membership, enabling stateless blockchain clients that don't store full state.

Which of the following best describes the security model of a hardware security module (HSM) in enterprise blockchain deployments?

Answer: HSMs perform cryptographic operations internally so private keys never leave the secure boundary

HSMs keep private keys within a tamper-resistant physical boundary, performing signing operations internally so keys are never exposed to the host system.