CBCP Cryptography 4 — Questions and Answers
Question 1: What is the BIP-39 standard primarily used for in cryptocurrency wallets?
- Defining the elliptic curve parameters for key generation
- Encoding a wallet seed as a human-readable mnemonic phrase (Correct answer)
- Specifying the format for multi-signature transactions
- Standardizing the encryption of private keys at rest
Correct answer: Encoding a wallet seed as a human-readable mnemonic phrase
BIP-39 defines how to encode 128-256 bits of entropy as a 12-24 word mnemonic phrase from a fixed wordlist, making wallet backup human-friendly.
Question 2: What is the key difference between ZK-SNARKs and ZK-STARKs?
- SNARKs use symmetric keys while STARKs use asymmetric keys
- STARKs do not require a trusted setup ceremony and are quantum-resistant (Correct answer)
- SNARKs produce larger proofs but verify faster than STARKs
- STARKs are limited to arithmetic circuits while SNARKs support any computation
Correct answer: STARKs do not require a trusted setup ceremony and are quantum-resistant
ZK-STARKs rely only on hash functions (making them quantum-resistant) and require no trusted setup, unlike ZK-SNARKs which need a trusted ceremony and use elliptic curve pairings.
Question 3: In the context of public-key cryptography, what does 'key encapsulation' accomplish?
- It wraps a symmetric key inside an asymmetric encryption operation for secure transmission (Correct answer)
- It stores a private key inside a hardware security module
- It derives multiple child keys from a single parent key
- It binds a public key to an identity via a certificate authority
Correct answer: It wraps a symmetric key inside an asymmetric encryption operation for secure transmission
Key encapsulation mechanisms (KEMs) use asymmetric cryptography to securely transmit a symmetric session key, which then encrypts the actual data more efficiently.
Question 4: Which attack exploits the birthday paradox to find hash collisions more efficiently than brute force?
- Pre-image attack
- Length extension attack
- Birthday attack (Correct answer)
- Side-channel attack
Correct answer: Birthday attack
A birthday attack exploits the birthday paradox: finding any two inputs with the same hash requires only approximately √(2^n) operations rather than 2^n, halving the effective security bits.
Question 5: What property does a cryptographic accumulator provide that a Merkle tree also provides?
- Ordered transaction sequencing with timestamps
- Compact membership proofs for elements in a set (Correct answer)
- Homomorphic encryption of set elements
- Threshold signing over a dynamic set
Correct answer: Compact membership proofs for elements in a set
Both cryptographic accumulators and Merkle trees enable compact proofs of membership (and sometimes non-membership) for elements in a large set.
Question 6: What is the main cryptographic purpose of HMAC compared to a plain hash?
- HMAC produces a longer output for stronger collision resistance
- HMAC authenticates both message integrity and the identity of the sender by incorporating a secret key (Correct answer)
- HMAC is reversible given the key, enabling decryption
- HMAC uses asymmetric keys to eliminate the need for a shared secret
Correct answer: HMAC authenticates both message integrity and the identity of the sender by incorporating a secret key
HMAC (Hash-based Message Authentication Code) combines a secret key with the message hash, so only parties holding the key can verify or produce a valid MAC.
Question 7: Why is the discrete logarithm problem central to the security of elliptic curve cryptography (ECC)?
- It ensures that the curve has a prime-order subgroup free of small subgroups
- Given a public key (point on the curve), it is computationally infeasible to find the private key (scalar) (Correct answer)
- It guarantees that all curve points have the same bit length as the private key
- It prevents side-channel leakage during scalar multiplication operations
Correct answer: Given a public key (point on the curve), it is computationally infeasible to find the private key (scalar)
ECC security relies on the elliptic curve discrete logarithm problem (ECDLP): given points P and Q=kP, finding the scalar k is computationally infeasible on properly chosen curves.
CBCP Cryptography 4
What is the BIP-39 standard primarily used for in cryptocurrency wallets?