Concepts
19 explainers
The building blocks behind every chain profile — each explained at three depths, grounded in MIT curriculum.
Consensus
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Byzantine Fault Tolerance
A consensus property where the system stays correct even when some participants are malicious — not merely offline. Byzantine Agreement guarantees honest players end on one value, even with traitors in the room.
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Delegated Proof of Stake
A Proof of Stake variant where token holders vote for a small set of delegates who produce blocks and validate transactions. Misbehaving delegates can be voted out.
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Distributed Consensus
The problem of getting many computers to agree on a value — or a sequence of values — despite faults: machines that crash, go offline, or actively attack. Blockchains use it to agree on the ledger itself.
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Proof of Stake
A consensus mechanism that chooses the next block producer by a lottery weighted by stake rather than by computation. Validators post tokens as collateral; misbehavior risks losing the stake.
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Proof of Work
A consensus mechanism where miners repeatedly hash block data with a varying nonce until they find a hash with the required number of leading zeros — proving they expended real computation. The longest-chain rule resolves forks.
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Pure Proof of Stake and Cryptographic Sortition
Algorand's consensus design: no forks, no miners, no Proof of Work. Each user runs a private, stake-weighted lottery (cryptographic sortition) to join a fresh committee for each step of a fast, player-replaceable Byzantine Agreement.
Cryptography
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Blockchain Privacy and Zero-Knowledge Proofs
Most chains are fully public (good for verification, bad for confidentiality) or fully anonymous (no regulator insight). Zero-knowledge proofs enable a middle path: private transactions that still support provably correct audits.
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Hash Functions
A function that turns data of any size into a fixed-size fingerprint. Deterministic (same input, same output, anywhere), effectively one-way (can't be reversed), and avalanche-sensitive (a tiny input change produces a totally different output).
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Public-Key Cryptography and Digital Signatures
Key generation produces a public key (a shareable identifier) and a secret key (never shared). Signing a transaction with the secret key proves consent and guarantees integrity — signatures are unforgeable and message-specific.
Data Structures
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Merkle Trees
A structure that compresses all transactions in a block into a single block-header hash, enabling efficient proof that one transaction is included — without scanning the whole block.
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The Blockchain (Three Properties)
Micali's framing: a blockchain is data in blocks that is readable by all, writable by all, and tamper-proof for all — blocks encased in bulletproof glass and chained in order.
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UTXO Model
Bitcoin tracks coins, not account balances. Coins are consumed in their entirety and spent once; an input references a previous transaction's output, and the sum of inputs must cover the sum of outputs — no money from nowhere.
Security
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51% Attack
If one party controls a majority of a network's power — hashing power in Proof of Work, staked tokens in Proof of Stake — it can monopolize block production, censor others, and reverse its own transactions.
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Double-Spend Problem
Digital tokens are copyable, so the core problem of digital money is ensuring a coin is spent only once. Banks used to guarantee this; Bitcoin had to solve it without one.
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Sybil Attack
When identities are cheap to create, an attacker can spin up many fake identities and subvert any vote-based system. Bitcoin had to solve this to achieve consensus among unknown participants.
Economics
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Mining and Mining Economics
Mining is performing Proof of Work to append blocks and earn the block reward plus fees. A hardware arms race — CPU to GPU to FPGA to ASIC — turned it into an industry sited near cheap power.
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Monetary Policy and Stablecoins
A currency's value rests on collateral (quality, liquid assets) and trust (independent management aiming at price stability). Fixed-supply crypto protocols can't stabilize — excitement pushes price up, fear down — which is the volatility stablecoins try to engineer away.