CBCP Cryptography 2 — Questions and Answers
Question 1: Which elliptic curve is used by Bitcoin for its digital signature scheme?
- P-256
- secp256k1 (Correct answer)
- Curve25519
- P-384
Correct answer: secp256k1
Bitcoin uses the secp256k1 elliptic curve defined in the SEC standard for its ECDSA signature scheme.
Question 2: What property ensures that a cryptographic hash function cannot be reversed to find the original input?
- Collision resistance
- Avalanche effect
- Pre-image resistance (Correct answer)
- Second pre-image resistance
Correct answer: Pre-image resistance
Pre-image resistance means it is computationally infeasible to find an input that produces a given hash output.
Question 3: In Ethereum's signature scheme, what is the purpose of the 'v' value returned alongside r and s?
- It encodes the transaction nonce
- It indicates signature validity
- It allows recovery of the public key from the signature (Correct answer)
- It specifies the hash algorithm used
Correct answer: It allows recovery of the public key from the signature
The 'v' recovery identifier allows the verifier to reconstruct the public key directly from the signature and message hash.
Question 4: What is a Merkle proof used for in blockchain systems?
- Encrypting transaction data end-to-end
- Proving a transaction is included in a block without downloading the full block (Correct answer)
- Generating new wallet addresses from a seed
- Creating zero-knowledge proofs for private transactions
Correct answer: Proving a transaction is included in a block without downloading the full block
A Merkle proof provides a compact set of hashes that allows a lightweight client to verify inclusion of a transaction in a Merkle tree.
Question 5: Which type of encryption scheme does Diffie-Hellman key exchange establish?
- A shared symmetric key over an insecure channel (Correct answer)
- An asymmetric private key pair
- A digital certificate for authentication
- A one-time pad for message encryption
Correct answer: A shared symmetric key over an insecure channel
Diffie-Hellman allows two parties to derive a shared symmetric secret over a public channel without ever transmitting the secret itself.
Question 6: What does 'key derivation' accomplish in the context of HD (Hierarchical Deterministic) wallets?
- It encrypts the master seed using AES-256
- It generates a tree of child keys from a single master seed (Correct answer)
- It converts a private key into a public key
- It creates a zero-knowledge proof of key ownership
Correct answer: It generates a tree of child keys from a single master seed
HD wallets use BIP-32 key derivation to produce an unlimited tree of child key pairs from one master seed, enabling backup of all keys from a single phrase.
Question 7: Why is a nonce included in a block hash computation for proof-of-work?
- To sign the block with the miner's private key
- To provide a variable field that miners iterate to find a hash below the target difficulty (Correct answer)
- To prevent double-spending of transactions
- To encrypt the block contents from observers
Correct answer: To provide a variable field that miners iterate to find a hash below the target difficulty
The nonce is the only field miners freely change; by iterating it, they search for a hash output that satisfies the network's difficulty target.
CBCP Cryptography 2
Which elliptic curve is used by Bitcoin for its digital signature scheme?