“There are 3 eras of currency: Commodity based, politically based, and now, math based.”—Chris
Dixon. Because as Tyler Winkelvoss states blockchain is awesome technology. “It’s a mathematical
framework that is free of politics and human error”.


Before describing the Blockchain, we will start clarifying what is NOT Blockchain. Many people
misunderstand the terms and concepts, leading to typical mistakes like the followings:

Blockchain is NOT a cryptocurrency.
“Blockchain is the tech. Bitcoin is merely the first mainstream manifestation of its potential.
Blockchain is NOT a programming language.
Blockchain is NOT a cryptographic codification.
Blockchain is NOT an IA or Machine Learning technology.
Blockchain is NOT a Python library or framework.

If you thought that Blockchain corresponds to one of the previous ideas, do not worry. You will soon
understand why you were wrong.


Blockchain is the name of a whole new technology. As the name states, it is a sequence of blocks or
groups of transactions that are chained together and distributed among the users.

“The blockchain is an incorruptible digital ledger of economic transactions that can be programmed
to record not just financial transactions but virtually everything of value.”– Don & Alex Tapscott.
In the end, it works as an immutable record of transactions that do not require to rely on an external
authority to validate the authenticity and integrity of the data. Transactions are typically economic,
but we can store any kind of information in the blocks.

Even when we call it ‘new technology’, its origins are accepted to date from 1991 when Scott and
Stornetta published “How to Time-Stamp a Digital Document” in the Journal of Cryptography.
However, it is now when its popularity has increased thanks to the success of Bitcoin and other


The value of the Blockchain technology comes from the distributed security of the system. For this
reason, there are several characteristics that are completely necessary for developing or using a

We describe the 5 key concepts that are the basis of the Blockchain technology as we know it up to
the date, based on the SuperDataScience course for Blockchain:
Cryptographic Hash
Immutable Ledger
P2P Network
Consensus Protocol
Block Validation or ‘Mining’


A Hash is a cryptographic function that transforms any input data into a fixed-length string of
numbers. Every single input of the hash function will produce a different output, and the result is
deterministic: if you use the same input, the output value will be always the same.
One of the most important features of the Hash functions is that the conversion is one-way: you
cannot reverse the function to generate the original input.

The Hash function generates a unique code from every different input
There are many algorithms to create different Hash variations. You can check how the SHA256 Hash
algorithm works here. For every input, the algorithm generates a completely different output, and it
is not possible to predict how will the input changes affect the output.
The Blockchain nodes use Hash functions to create a unique identifier of any block of transactions.
Every block includes the Hash value of the previous block.


This feature is tightly related to the previous one. Since every block of the chain contains the Hash of
the previous one, it is not possible to modify any block without changing the entire chain. Hence, the
chain works as an immutable digital ledger.

Let us see an example. We have the following chain, in which every block has been hashed and the
hash is included in the following one:

If an anonymous attacker removes, adds or modifies any transaction in the first block, the HASH#1
will change:

HASH#1 is included as a part of the contents in Block 2. Because of that, HASH#2 will change too, and
the error will propagate to every block of the chain after the block under attack. The user will then
declare the chain invalid.


The Blockchain does not need any external or internal trust authority. This is possible because the
Blockchain data is distributed among all the users. Every user has its own copy of the transactions
and hashed blocks, and they spread the information of any new transaction to the entire network.

This way, it is not possible for anyone to alter the information in the chain since it is not stored by an
individual entity but for an entire network of node users.

Once a block of transactions is validated, it is added to the chain and every user update their local
information. Even if an attacker were to modify your local chain, the network will not accept any
block from the altered blockchain.


But what is the real blockchain? Users need to meet an agreement about the validity of the chain
before adding more blocks.
Every time a node adds a new block, all the users have to validate the block by using a common
protocol. Typically, the nodes reach a consensus about the correctness of a new block by Proof of
Work or Proof of Stake methods.

The nodes check that the new block meets the requisites of their Proof method, including validation
for all the transactions inside the block. If the block is valid, they consider it as a part of the
Blockchain and keep adding new blocks.

Every user has its own copy of the Blockchain, and they share any update with the other users
In the case that different users have different chains apparently valid, they will discard the shorter
one and select the longest chain as the main Blockchain. As in any Byzantine Fault Torelance (BFT)
system, they will meet an agreement about the correct chain while at least 2/3 of the total nodes are
not malicious.


This feature is actually not completely necessary for a Blockchain, as we can see with examples like
the CREDITS platform. However, is it probably one of the most famous facts about Blockchain thanks
to the Bitcoin chain.

The term ‘mining’ refers to the act of meeting the Proof of Work requirements for adding a new
block with pending transactions to the Blockchain. There are many different mining methods, as they
are custom defined for the chain.

Mesmerizing Black And White GIF by xponentialdesign

The PoW method usually requires the user to create a block with restrictions on its Hash code. Since
the Hash code is unpredictable, the ‘miners’ have to test any possible combination before meeting
the requirements. These restrictions define the difficulty of the network.

Once a ‘miner’ node finds the solution to the PoW problem, they add the block to the chain and
every other node check the validity of the PoW according to their Consensus Protocol. If the block is
legit, they will include it on their own local copies of the Blockchain.


The Blockchain technology is permanently evolving. However, we can find some key pillars to sustain
the added value of this technology.

The Blockchain allows users to create a reliable and immutable system for recording any kind of
transaction or information. There is no need for an external or internal authority: every user relies on
the technology itself, following predefined rules to meet consensus and ensure the integrity and
authenticity of the data.

Source: Telmo Subira Rodriguez,

Blockhain for Dummies: