Blockchain Architecture

A Blockchain is a chain of blocks which contain information. The data which is stored inside a block depends on the type of blockchain.

A block also has a hash. It can be understood as a fingerprint which is unique to each block. It identifies a block and all of its contents, and it's always unique, just like a fingerprint. So once a block is created, any change inside the block will cause the hash to change.

Each Block has

1. Data

2. Hash

3. Hash of the previous block

Proof of Work:

A proof-of-work is a computational problem that takes certain effort to solve. But the time required to verify the results of the computational problem is very less compared to the effort it takes to solve the computational problem itself.

This kind of mechanism makes it quite tough to tamper with the blocks so even if you tamper with even a single block, you will need to recalculate the proof-of-work for all the following blocks. Thus, hashing and proof-of-work mechanism make a blockchain secure.