Blockchain Fundamentals - Unit 1 & Core Concepts

Comprehensive vocabulary flashcards covering the core concepts, architecture, cryptography, account types, and structures of Unit 1 in Blockchain Fundamentals.

Blockchain

A distributed, append-only ledger of transactions, replicated across many independent computers, where each new block of records is cryptographically linked to the one before it, and where the network agrees on the single valid history through a consensus mechanism without any central authority.

Distributed Ledger

A ledger architecture where records are copied, in full or in part, across thousands of independent computers called nodes, eliminating any single server or primary copy to restore from.

Append-only

A ledger property meaning new records can be added, but existing records cannot be edited or erased; any error is corrected by adding a new compensating entry.

Consensus Mechanism

The set of network rules that enables thousands of independent nodes that do not know or trust each other to agree on which transactions occurred and in what order.

The Oracle Problem

The vulnerability and limitation at the interface between the physical world and the blockchain (such as a scale, sensor, or clerk), where real-world facts can be falsely reported and the blockchain will preserve that error immutably.

Smart Contract

A computerised transaction protocol that automatically executes the terms of a contract, originally conceptualised by Nick Szabo between $1994$ and $1996$.

Cryptographic Hash Function

A mathematical algorithm that takes an input of any size and produces a fixed-size digest that is deterministic, fast to compute forward, pre-image resistant, collision resistant, and exhibits the avalanche effect.

Pre-image Resistance

The cryptographic property of a hash function that makes it computationally infeasible to determine the original input given only its hash output.

Avalanche Effect

The property of a hash function where changing even a single bit of input unpredictably alters approximately half of the output bits.

Collision Resistance

The cryptographic property of a hash function ensuring that it is practically impossible to find two distinct inputs that yield the exact same hash output.

Keccak-256

The cryptographic hash function variant of SHA-3 used by Ethereum, which produces a $256$-bit ($32$-byte) digest represented as $64$ hexadecimal characters.

Asymmetric Cryptography

A cryptographic system where each party holds a mathematically linked key pair: a secret private key and a public key derived via a one-way mathematical function.

secp256k1

The specific elliptic curve used by both Ethereum and Bitcoin for elliptic curve cryptography.

Ethereum Address

The last $20$ bytes of the Keccak-256 hash of a public key, prefixed with '0x' and displayed as $40$ hexadecimal characters.

Digital Signature

A cryptographic proof constructed via ECDSA that simultaneously confirms authenticity (who signed), integrity (the data has not changed), and non-repudiation (the signer cannot deny it).

EIP-55

An Ethereum address checksum standard where mixed capitalization in the hexadecimal address encodes a checksum to prevent funds from being sent to mistyped addresses.

Hierarchical Deterministic (HD) Wallet

A wallet standard governed by BIP-32, BIP-39, and BIP-44 that generates an entire tree of child keys deterministically from a single master seed.

Mnemonic Seed Phrase

A sequence of $12$ or $24$ words from a standard dictionary of $2,048$ words that encodes $128$ or $256$ bits of initial randomness used to derive an HD wallet master seed.

Derivation Path

A structured path (such as m/44'/60'/0'/0/x for Ethereum) specifying the exact route down a hierarchical deterministic tree to derive a specific child key from the master private key.

Transaction

A cryptographically signed instruction issued by an externally owned account that requests a state change on the blockchain.

Nonce

An Ethereum transaction field indicating the exact count of transactions previously sent by an account, used to enforce ordering and prevent replay attacks.

Externally Owned Account (EOA)

An Ethereum account controlled directly by a private key, which is the only account type capable of initiating transactions.

Contract Account

An Ethereum account governed purely by its deployed smart contract code rather than a private key, which only executes when called by an external account or another contract.

Merkle Tree

A data structure that repeatedly hashes pairs of data nodes together until arriving at a single root hash, allowing logarithmic proof of membership without revealing the entire dataset.

Merkle Root

A single $32$-byte hash representing the apex of a Merkle tree that cryptographically commits to all child leaves beneath it.

parentHash

A block header field containing the cryptographic hash of the preceding block's header, establishing the tamper-evident link that binds the chain together.

Public (Permissionless) Blockchain

A blockchain where anyone can view data and anyone complying with protocol rules can validate and post transactions (such as Bitcoin or Ethereum).

Private (Permissioned) Blockchain

A blockchain restricted to invited participants for viewing, with writing and validation handled exclusively by designated, vetted nodes (such as Hyperledger Fabric).

Consortium (Federated) Blockchain

A blockchain where reads are open to members or the public, but validation and writing rights belong to a predefined coalition of organisations.

Finality

The state or point in time after which a blockchain transaction is considered completely irreversible by network consensus.

Anchoring (Notarisation)

The technique of storing the cryptographic hash of an off-chain document or dataset on a blockchain to prove its existence and integrity at that exact point in time.

Self-Sovereign Identity (SSI)

An identity paradigm where individuals store verifiable credentials directly inside their personal wallets and disclose selective attributes without relying on a central server.

The Merge

The major $2022$ Ethereum network upgrade that transitioned consensus from proof-of-work to proof-of-stake, reducing energy expenditure by over $99\%$.