Blockchain Technology Cryptographic Principles 3

Question 1

Which hashing algorithm does Bitcoin use to produce block header hashes during proof-of-work mining?

Accepted Answer

SHA-256 (applied twice)

Answer

Bitcoin applies SHA-256 twice (SHA-256d) to compute the block header hash used in proof-of-work.

Question 2

In the secp256k1 curve used by Bitcoin, what is the typical size of an uncompressed public key?

Accepted Answer

65 bytes

Answer

An uncompressed secp256k1 public key is 65 bytes: a 0x04 prefix followed by two 32-byte coordinates (x and y).

Question 3

What cryptographic operation converts a Bitcoin public key into a Bitcoin address?

Accepted Answer

SHA-256 then RIPEMD-160, followed by Base58Check encoding

Answer

Bitcoin addresses are derived by hashing the public key with SHA-256 then RIPEMD-160, and encoding the result with Base58Check.

Question 4

Which property ensures that a small change in input produces a drastically different hash output, making hash outputs unpredictable?

Accepted Answer

The avalanche effect

Answer

The avalanche effect means that flipping even a single bit in the input causes approximately half the output bits to change.

Question 5

In asymmetric cryptography, if Alice wants to send Bob a confidential message, which key does she use to encrypt it?

Accepted Answer

Bob's public key

Answer

Alice encrypts with Bob's public key so that only Bob, holding the corresponding private key, can decrypt the message.

Blockchain Practice Test