Blockchain and Its Structure - An Introduction


The term 'Blockchain' is holding its place in top technologies and we can't see a day without hearing the news about bitcoin, blockchain, cryptocurrency, etc. So, I believe it is necessary to know at least the basics of Blockchain. In this article, I will explain the concept of Blockchain.
  • What is Blockchain?
  • Blockchain-Structure
    • How is the chaining of the block done?
    • Why are records in the blocks said to be immutable?
  • How is Blockchain secure?
Though the origin of Blockchain's is in 1991, after the publishing of "How to Time-Stamp a Digital Document," in the Journal of Cryptography by Scott and Stornetta, its popularity increased after the highest reach of the Bitcoin's value (to about $20,000) in the year 2017.

What is Blockchain?

As the term indicates, Blockchain is a chain of blocks containing a group of transactions or digital data, that are distributed among the millions of users or nodes. The transactions may contain information of any kind. Since the blocks are chained together, its data can never be changed again, i.e. the records stored are immutable. The chaining of the Blocks is done with a hash value of each block.
Blockchain And It's Structure
The information stored in Blocks is shared with the cluster of users in the distributed structure and hence there is no term called "central authority" in the Blockchain. Since the blocks are distributed, if anyone is in need to alter the information, he/she needs to alter the data in all the nodes, which is not possible. Hence, security and trust increase while using Blockchain.


A single block of the Blockchain contains,
  • Hash of the block
  • Timestamp
  • Group of Transactions
  • Previous block's Hash value
Each block contains a unique identifier called a "Hash value". The Hash value is stored in the header of the Block.
Blockchain And It's Structure

How is the chaining of the block done?

The signature or hash is created using the Cryptographic Hash Function. The cryptographic hash function takes any input string and gives the 64-bit hash value as the output. It gives the same output for the same input, but a unique output for the different input.
Bitcoin uses SHA-256 as the cryptographic hash function. The hash function works in a single way (i.e. we can't get the input string using the hash value).
The size of each block in the Blockchain will be the same. Let assume that the Block size is 1MB and 4 Transactions of 200 KB each is made. The first 4 transactions are grouped and stored as Block 1. Then Block 1 gets its unique signature called hash value (Hash1) and the Hash 1 of Block 1 is stored as the data of Block 2. Block 2 with its data (transactions +Hash 1) gets its own unique signature, which is stored in the data part of Block 3. This way, by storing the Previous Block's Hash Value, the chaining of the Blocks is made.
Blockchain And It's Structure

Why are records in the blocks said to be immutable? 

Let say from the above example, if anyone is trying to falsify data in Block 1, the hash value of Block 1 will be changed. Since Block 2 holds the hash value of Block 1, the hash value of Block 2 will also get changed. This will also affect the hash value of Block 3 and it continues. So, the change in single block data requires the change in the entire chain, which is not possible. This makes the block immutable.
Blockchain And It's Structure

How is Blockchain Secure?

  • The main reason is the distributed nature. Since the data is stored in many nodes, the person who tries to alter the record may need to alter the records in all the nodes. If a person tries to modify the block, the network will not accept the block.
  • Cryptography also helps to secure the data in the block.
  • Though any users can access the details about the transactions, they cannot gain personal information about the person making the transaction. Hence, the anonymity of the user is maintained.
  • Blocks are immutable, therefore it is not an easy task to alter the information in the Block.


Blockchain is the distributed chain of blocks that contains a group of transactions stored in a secure way. It provides trust and data security. It is now vastly evolving in the areas of Financial Industry, Healthcare, Supply Chain Management, Real Estate, Food Safety, Copyright, and royalty protection, etc., So, Blockchain will surely change the life of many people in the upcoming years.

Similar Articles