How does Blockchain use hashing? Select all that apply.

Hashing is a fundamental cryptographic primitive used in multiple critical blockchain functions.
1. It condenses all transactions within a block into a single fixed-size hash called a Merkle Root. This allows for efficient verification of data integrity, as comparing a single hash is much faster than comparing all transaction data (A).
2. It creates an immutable, chronological chain by including the hash of the previous block's header in each new block. This ensures that any alteration to a previous block would change its hash, breaking the chain (B).
3. In Proof-of-Work (PoW) consensus mechanisms, nodes (miners) repeatedly hash the block header with a nonce until they find a hash that meets a specific difficulty target. The node that finds this hash is effectively selected to add the next block to the chain (D).

C. Public key cryptography is used for digital signatures to prove ownership. Hashing creates addresses from public keys, providing pseudonymity, but it is not the mechanism for anonymity itself.
E. This option is incorrect because option C is not a valid use of hashing in the context described.

1. Narayanan, A., Bonneau, J., Felten, E., Miller, A., & Goldfeder, S. (2016). Bitcoin and Cryptocurrency Technologies: A Comprehensive Introduction. Princeton University Press.

For A & B: Section 1.2, "How Bitcoin Achieves Decentralization," p. 6-7, explains how blocks contain the hash of the previous block (chaining) and how transactions are hashed into a Merkle tree to create a single hash for the block.

For D: Chapter 2, "How Bitcoin Works," Section 2.3, "Proof of Work," p. 34-36, details how miners compete by hashing to find a value below a target, which determines which node's block is added to the chain.

2. Antonopoulos, A. M. (2017). Mastering Bitcoin: Programming the Open Blockchain (2nd ed.). O'Reilly Media.

For A: Chapter 9, "The Blockchain," section "Merkle Trees," describes how transaction hashes are aggregated into a Merkle root to summarize and condense transaction data.

For B: Chapter 9, "The Blockchain," section "Block Headers," explains that the "Previous Block Hash" field directly links a block to its predecessor, forming the chain.

For D: Chapter 10, "Mining and Consensus," section "Proof-of-Work Algorithm," details the process of finding a valid hash to win the right to add a block to the blockchain.