Blockchain Fundamentals and Distributed Ledger Technology Concepts
What this domain tests
The exam checks whether you can separate blockchain from adjacent ideas: distributed databases, public cryptocurrencies, and simple replicated systems. Expect questions on hash linking, Merkle roots, transaction lifecycle, node roles, and public versus permissioned DLT.
Core rules
- A blockchain is an append-only ledger of cryptographically linked blocks; each block header commits to the previous header and a Merkle root of its transactions.
- A DLT is broader: it may use a DAG, hashgraph, or replicated state machine without blocks.
- Distributed means copies exist across nodes; decentralized means no single party controls writes. A permissioned network can be distributed but centrally governed.
- Immutability is economic and social as well as technical: rewriting history requires controlling consensus plus convincing participants to accept the new state.
- Public networks usually use pseudonymous key pairs; enterprise networks bind identities through membership services.
- Transaction finality differs: probabilistic in proof-of-work, deterministic in many BFT protocols.
Worked example
A block contains transactions T1-T4. Its Merkle root is H(H(T1)||H(T2)) || H(H(T3)||H(T4)). If an attacker changes T3, the Merkle root changes, the block header changes, and every later block header fails validation. The reasoning: you cannot edit one record without recomputing all descendants and outrunning consensus.
Traps
Do not say blockchain equals Bitcoin. Do not call a replicated database a blockchain if no party can independently verify history. Do not claim absolute immutability; private networks can reorganize by governance. Do not confuse a hash with encryption - hashing is one-way and does not hide low-entropy data.