Blocks

A Blockchain is called so because it is designed as a series of transactions conceptually grouped in blocks chained together in sequence. In this design, no transaction record can be modified or deleted, thus guaranteeing the validity of all transactions and allowing them to be verified or audited by any participant at any point in time.

Blocks are secured using cryptography and public-private key encryption and further linked together in a chain using a complex hashing mechanism. These measures make malicious attempts to access or modify the data very difficult if not impossible.

Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data. The timestamp proves that the transaction data existed when the block was created. Since each block contains information about the previous block, they effectively form a chain, with each additional block linking to the ones before it. Consequently, blockchain transactions are irreversible in that, once they are recorded, the data in any given block cannot be altered retroactively without altering all subsequent blocks.