Technology & AI
Blockchain, simply.
A shared digital record book that makes it difficult to secretly rewrite the past.
It helps independent people or organizations agree on a history. Its main security benefit is protecting that record. Bitcoin is one use of blockchain; certificates and document proofs are others.
Start here: NIST's blockchain overview.
Imagine a notebook everyone can check
Three friends track shared expenses. Several computers keep copies of their notebook, and new entries must follow agreed rules. Editing one copy does not automatically change the accepted history.
A block is like a page of entries. The chain connects each page to the one before it. A node is a computer participating in the network. Bitcoin's explanation · Ethereum's blocks guide
Change one record and watch the link break
A hash is a mathematical fingerprint. Each block links to the previous block's fingerprint. Changing an earlier record changes its fingerprint, so the next block's saved link no longer matches.
Block 1
Start of notebook
- Previous fingerprint
- none
- This fingerprint
- aa1ccded
Block 2 changed
Alex → Sam: 5 tokens
- Previous fingerprint
- aa1ccded
- This fingerprint
- 07a8e86d
Block 3 changed
Sam → Jo: 2 tokens
- Previous fingerprint
- 07a8e86d ≠ mismatch
- This fingerprint
- 1273c58a
Links match. This is the original history.
Rebuilding the links does not make the new history accepted. Other participants still check transactions and follow their agreement rules, called consensus. Bitcoin uses computational work. Ethereum uses validators who put ETH at risk and can be penalized for misconduct. It is not simply one vote per computer.
How blocks link · Bitcoin consensus · Ethereum proof of stake
Four ingredients working together
- Hashes
- Fingerprints that make changes detectable. A hash is not encryption.
- Digital signatures
- Approval stamps proving that the matching private key authorized a transaction.
- Distributed copies
- Several copies that participants can check independently.
- Consensus
- Rules for deciding which valid history the network follows.
Ethereum blocks · Bitcoin signatures and consensus
Technologies using blockchain for security
Each protects a particular kind of record. Open a row to see the benefit and its limits.
BitcoinPayment history
A shared payment history helps prevent spending the same coins twice. Digital signatures authorize spending.
Still depends on: protecting your keys and wallet. A stolen key can authorize a real transaction.
How Bitcoin works ↗EthereumProgrammable rules and digital assets
A smart contract is a program on a blockchain. Picture a vending machine: a valid input triggers a programmed result.
Still depends on: the code and its permissions. Bugs can be exploited, and outside information can be wrong. A program does not judge fairness.
Smart contracts ↗ · Contract security ↗Hyperledger FabricRecords shared by approved organizations
A blockchain framework with identities and policies governing who can approve transactions or access records. This is a permissioned network.
Still depends on: the participating organizations, their identity authorities, and their policies.
Fabric's security model ↗OpenTimestampsProof that a file existed
Uses Bitcoin to create independently checkable proof that a particular file existed before a point in time. A fingerprint can be recorded without publishing the file itself.
Still depends on: what the file claims. A timestamp does not prove authorship or truth.
How OpenTimestamps works ↗BlockcertsVerifiable diplomas and credentials
An open standard for issuing and checking blockchain credentials, including diplomas and professional licenses.
Still depends on: the issuer's identity and credibility. A verifiable certificate does not make a dishonest issuer trustworthy.
Blockcerts guide ↗What it does not automatically protect
- Privacy. Public blockchains usually expose transaction data. Privacy takes additional design.
- Real-world truth. Recording “the package arrived” does not prove it arrived.
- Your devices or secret keys. The surrounding systems still need protection.
- Every network equally. Concentrated control or weak governance can undermine security.
Blockchain is useful when independent parties need a common history without handing control to one party. If one trusted organization can manage the records, a conventional database is often simpler.
NIST's full technology overview
Four graphic ideas to remember
- Shared notebooks
- Three matching copies; one altered copy stands out. One changed copy does not rewrite history.
- Fingerprint chain
- Change one entry and highlight the next link's mismatch.
- Certificate check
- Compare a diploma's fingerprint with its recorded proof. Check the record, then the issuer.
- Vending machine
- A valid input passes through rules to a programmed output. A smart contract follows its code.