Blockchain
What is Blockchain ?
Blockchain is an emerging and a revolutionary technology that can be used to securely communicate into a distributed network.
Why Blockchain ?
So, the question arises how is blockchain a revolutionary technology. Well it’s just a simple concept which eliminates the involvement of a third party.
Take an example of a transaction. Suppose person A wants to send money to person B. The transaction is generally validated by a third party called bank. The downside of this procedure is that we have to trust this third party, bank charges some fee for transaction and usually it takes 3–4 days for validating the transaction.
What if we could eliminate this third party! We could save time, money and we don’t have to trust anybody for our transactions. Wouldn’t that be great. The same concept is used in bit
coins which works under the blockchain technology.
How blockchain works !
As blockchain eliminates the involvement of third party, then how to validate the communication. This is done by maintaining a database of all the communication that took place from the very beginning. This database is called a ledger. A copy of this ledger is kept with every node on the network.
Whenever a new communication data is initiated, the data is sent to be validated to special nodes who volunteer to validate the data. In bitcoin network, these special nodes are called miners. These special nodes then validate the data by reading from the ledger that they have. The first one to validate the the data gets a reward (some bitcoins in case of bitcoin network). Whenever some node validates the data, the data gets saved in a block kept with that node. Each block has a fixed size. Whenever the block gets filled, the whole block gets added to the ledger and the ledger gets updated for every node in the network.
The next problem is how could we trust the node that is validating the data. This problem is solved by a concept called proof of work. The way it works is that all miners compete to find a number that, when added to the block of transactions, causes this block to hash to a code with certain rare properties. In bitcoin network, this rare property is that the SHA-256 hash of all data must start with 10 zeroes. Therefore this is a problem which is difficult to achieve but very easy to verify. Therefore whenever a node says that it has validated some data, it is verified by other nodes and if it has more than 51% votes, then it gets added to the block.
The beauty of this concept is that we do not have to trust a node for validation but have to trust the system.

Every block in the ledger contains the identity of previous hash. Therefore if anyone could somehow delete a block from the ledger, then its ledger will not be valid and therefore his ledger will be updated to the original one. Thus the system is secure as to hamper the network, one has to change at least 51% of all the copies of the ledger which is not possible.
