Blockchain is a shared, immutable digital ledger for recording transactions, tracking assets, and building trust.
The blockchain serves as a historical record of all transactions that occur starting from the genesis block*. Each block is linked to its preceding and succeeding blocks by a cryptographic hash, hence the name blockchain. In other words, a blockchain is a special type of immutable database also referred to as a digital ledger.
Blockchain may be either public or private. Data stored in a public blockchain is visible to everyone regardless of their roles in the blockchain. In a private blockchain, data can only be accessed by participating parties.
* The Genesis block is the first block of an entire blockchain. Each block not only contains its own hash (i.e. unique ID) but also the hash of the previous block. Since it is first, the genesis block is the only block that doesn’t have the latter. It is a special block that establishes the foundation and prototype for all other blocks in the blockchain.
What makes Blockchains secure?
There are three distinguishing features that make blockchain immune to hacking or alteration:
Immutable blocks Once data is written into a block and added to the blockchain, it is unalterable.
Distributed nodes – A network of multiple server computers store the same blockchain record, providing redundancy and protecting database integrity in the case of unexpected events on one of the blockchain copies on a node (or peer).
Consensus mechanism – A process where participating nodes (or peers) in a network validate the authenticity of transactions before adding the block to the blockchain.