Question 1

Is blockchain the same as Bitcoin?

Accepted Answer

No. A blockchain is the underlying data structure: a shared ledger of hash-linked blocks that can only be added to. Bitcoin is one application built on it, a cryptocurrency whose white paper was published on 31 October 2008 and whose first block was mined on 3 January 2009. Other public blockchains, such as Ethereum, run smart contracts. Permissioned platforms such as Hyperledger Fabric are used by known groups of organisations and do not need a public cryptocurrency.

Question 2

What is the difference between a public and a private blockchain?

Accepted Answer

Anyone can join a public (permissionless) blockchain. NIST describes it as a system where all users' permissions are equal and not set by any administrator. A private or consortium (permissioned) blockchain requires every node and user to be granted permission, usually by an administrator or consortium. Public chains such as Bitcoin and Ethereum use proof of work or proof of stake. Permissioned chains such as Hyperledger Fabric can use lighter ordering protocols, because their participants are known.

Question 3

Can a blockchain be hacked or changed?

Accepted Answer

Changing past records is hard but not impossible. Each block contains the hash of the previous block, so editing an old transaction means rebuilding every block after it. On a proof-of-work chain, that would take control of most of the network's computing power, known as a 51% attack. On Ethereum's proof-of-stake chain, it would take at least half of the staked ETH, and attackers can lose that stake. Wallets, keys and smart contract code can also be attacked separately.

Question 4

How much energy does blockchain use?

Accepted Answer

It depends on the consensus mechanism. Proof-of-work chains use a lot of electricity. The University of Cambridge's revised estimate put Bitcoin's use at 95.5 TWh in 2022. The U.S. Energy Information Administration estimated that crypto mining made up 0.6% to 2.3% of U.S. electricity consumption. Proof-of-stake chains use far less. Ethereum's energy consumption fell by an estimated 99.95% when it switched to proof of stake in September 2022.

Question 5

What is a smart contract on a blockchain?

Accepted Answer

A smart contract is a program stored on a blockchain. NIST defines it as a collection of code and data, deployed with cryptographically signed transactions, that the network's nodes run. Every node must get the same result, and the result is recorded on the chain. Smart contracts can automate things like token issuance or escrow. The OECD notes that making sure the code is correct and resolving disputes remain open challenges.

項目	値	出典
Definition (NIST)	Tamper-evident and tamper-resistant digital ledgers implemented in a distributed fashion, without a central repository時点 2018年10月3日	[1]
Central authority	Usually operates without a central authority such as a bank, company or government時点 2018年10月3日	[1]
Immutability	Under normal network operation, no transaction can be changed once published時点 2018年10月3日	[1]
US government reference document	NIST IR 8202, Blockchain Technology Overview (Yaga, Mell, Roby, Scarfone), DOI 10.6028/NIST.IR.8202時点 2018年10月3日	[1]
Typical use	The underlying technology of cryptocurrency systems時点 2018年10月3日	[2]
Foundational paper	"Bitcoin: A Peer-to-Peer Electronic Cash System" by Satoshi Nakamoto (pseudonym)	[3]
Notable consensus change (official claim)	Ethereum mainnet moved from proof of work to proof of stake (the Merge)時点 2022年9月15日	[4]
Ethereum energy reduction after the Merge (official claim)	About 99.95% (figure stated by the Ethereum project) percent時点 2022年9月15日	[4]
South Korea: crypto-asset regulation	Act on the Protection of Virtual Asset Users in force; requires bank custody of user deposits, segregation of assets and monitoring for unfair trading時点 2024年7月19日	[5]
South Korea: Act enacted	Act on the Protection of Virtual Asset Users enacted時点 2023年7月18日	[5]

Blockchain

Is blockchain the same as Bitcoin?

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Is blockchain the same as Bitcoin?

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