Blockchain

Distributed P2P network is a network in which different computers are connected to each other having same blockchain on each system.So if someone tries to attack or hack the blockchain it has to change the block and the block coming after it. Let's say you hacked a system/pc and changed the entire blockchain after a block but the connected computers having same blockchain communicate with this attacked system and the majority of right chain stops the blockchain to get hacked. In simple words to hack a blockchain a person needs to hack at least 50% of the computers/laptops to change the entire blockchain which is practically impossible because of the computational time taken for hacking and in this period the other systems corrected the chain (or the new validated blocks get added).

Ledger is a collection of entries of debits and credits and in general it is kept in a form of book or some excel sheet etc. which can be destroyed easily. For example:- The owner of a house has property documents in a file and someone changed it physically and make himself/herself the owner of same house. But when it comes to blockchain that mischievous person has to change that block of ledger as well as the block comes after it because the hash of each block is linked to the next block come after it. Since present hash is calculated using the previous hash,so if you are changing the present hash you need to change the next hashes otherwise the chain will not approve your calculated hash.In this way the blockchain has a property of Immutable ledger.

Hash cryptography is based on algorithm called SHA(Secure Hash Algorithm) which can be SHA-3,SHA-1,SHA-256 and many more. Here I am briefing SHA-256 where the data is represented in hexadecimal form which is 64 characters long made up of numbers (0 to 9) and and alphabets (a to f) each 4 bits long. Basically hash is like a fingerprint means unique. For example:- a document with hash     📄--> 0023a76bef63c568                  67dc128a3fe60a7e                d47b95a532b60a74                a62e73f026d957a3 Some properties of hash are- 1- Avalanche effect:- the hash will change with even a single change in document. 2- Deterministic:- the document will always give the same hash. 3:- One way:- one can calculate hash of a document but document can't find using the hash. 4:- Withstand with collision:- no one can have the same hash even when they have the same document otherwise the originality of documents will be lost.

When you search about blockchain the most repited definition can be seen is " A  blockchain , originally  block chain ,  is a growing list of  records , called  blocks , which are linked using  cryptography ."- by Wikipedia. But what actually these blocks contain and how it is linked and other technical stuffs are not shown in simple way. These blocks contain data which includes some parameters like the number of block, previous hash etc. which are needed to calculate the hash of present block. There are mainly five things to understand what actually the tech is. 1- Hash cryptography 2- Distributed P2P network 3- Immutable ledger 4- Consensus Protocol 5- Mining Each of these points are explained in next blogs but in simple way.