Cryptocurrency Cryptography and Hashing 5 — Questions and Answers
Question 1: What is a 'ring signature' used for in privacy-focused cryptocurrencies like Monero?
- To sign circular transactions between the same wallet
- To allow a user to sign a transaction on behalf of a group without revealing which member signed (Correct answer)
- To create a cryptographic loop that verifies block order
- To sign multiple outputs in a single Bitcoin transaction
Correct answer: To allow a user to sign a transaction on behalf of a group without revealing which member signed
Ring signatures let a signer produce a signature verifiable as coming from a group while hiding which specific group member actually signed.
Question 2: What is the primary purpose of the ECDSA (Elliptic Curve Digital Signature Algorithm) in Bitcoin?
- To encrypt wallet backup files
- To generate and verify transaction signatures proving ownership of funds (Correct answer)
- To hash block headers during mining
- To derive public keys from private keys using multiplication
Correct answer: To generate and verify transaction signatures proving ownership of funds
ECDSA is used to create digital signatures for Bitcoin transactions, allowing nodes to verify the sender owns the referenced UTXOs.
Question 3: What is 'replay protection' in the context of cryptographic transaction signing during a blockchain hard fork?
- Preventing miners from reusing block templates
- A mechanism ensuring a signed transaction on one chain cannot be rebroadcast on a forked chain (Correct answer)
- Encrypting transaction data so it can only be read once
- Preventing nodes from re-syncing the same block twice
Correct answer: A mechanism ensuring a signed transaction on one chain cannot be rebroadcast on a forked chain
Replay protection modifies transaction signing to include chain-specific data, so a valid transaction on one fork is invalid on the other.
Question 4: What distinguishes a 'trapdoor function' from a regular one-way function in public-key cryptography?
- A trapdoor function can be reversed only with a special secret (private key) (Correct answer)
- A trapdoor function is irreversible under all circumstances
- A trapdoor function produces shorter outputs than inputs
- A trapdoor function uses symmetric keys internally
Correct answer: A trapdoor function can be reversed only with a special secret (private key)
A trapdoor function is easy to compute forward and hard to reverse, except for someone who knows the secret trapdoor — the private key.
Question 5: What is the 'difficulty target' in Bitcoin mining, and how does hashing relate to it?
- A minimum transaction fee miners must collect
- A threshold the block's SHA-256 hash must be numerically below to be accepted (Correct answer)
- The number of leading zeros required in the Merkle root
- A limit on how many transactions can be included in a block
Correct answer: A threshold the block's SHA-256 hash must be numerically below to be accepted
Miners must find a nonce such that the block header's double SHA-256 hash is less than the current difficulty target, a number with many leading zeros.
Question 6: In Schnorr signatures (used in Bitcoin's Taproot upgrade), what key advantage do they offer over ECDSA?
- They use a larger key size for stronger security
- They are linearly aggregatable, allowing multiple signatures to be combined into one (Correct answer)
- They eliminate the need for private keys entirely
- They use SHA-512 instead of SHA-256
Correct answer: They are linearly aggregatable, allowing multiple signatures to be combined into one
Schnorr signatures support linear aggregation, so a multi-signature transaction can present a single aggregated signature indistinguishable from a single-signer one.
Question 7: What is a 'stealth address' in cryptocurrency privacy, and which cryptographic concept enables it?
- A hidden wallet address used only on the dark web, enabled by onion routing
- A one-time address generated per transaction using Diffie-Hellman key exchange so only the recipient can detect it (Correct answer)
- An encrypted alias for a public address stored on-chain
- A zero-knowledge address used in zk-SNARK proofs
Correct answer: A one-time address generated per transaction using Diffie-Hellman key exchange so only the recipient can detect it
Stealth addresses use ECDH (Elliptic Curve Diffie-Hellman) to let a sender generate a one-time address only the intended recipient's private key can detect and spend from.
Cryptocurrency Cryptography and Hashing 5
What is a 'ring signature' used for in privacy-focused cryptocurrencies like Monero?