TL;DR: In this series, we will talk from the very blockchain basics to building a complex DAPP.

Background

What is FIAT? 💰

The standard currency is called FIAT.
FIAT requires a middle man authority (a bank or a government as examples).
A cryptocurrency in some technology (like blockchain) relies on automatic rules to comply with the exchange rules.
The most widely used digital currencies are cryptocurrencies.
We call them crypto because it relies on mathematical cryptographic properties similar to password encryption.
We cannot trust other people around without a middle man.
We use cryptography to exchange value in the same way we use https to send sensitive data over the internet.

We have been using math hashes for a long time in computer science.
Hash functions take an input and produce a deterministic output.
We use hashes on databases, algorithms, and data structures.
A good hash function is easy to calculate on the input, but very hard (in computer time) to reverse from the output.
Multiplying two integers is a very fast operation.
Factoring an integer into its prime factors is a very expensive operation (provided factors are large enough).
We can transform any data on blockchain into numbers and encrypt them very fast.
If we chain a block content, its hash changes unless they have the same hash.
We called this a hash collision and can keep its probability near zero using math.

Blockchain is about decentralized trust.
You exchange value without an intermediate.
Trust issues are not solved by a middle man like a market, broker, credit card, or bank.
You don't trust or rely on reputation or a certified third party.
Standard middlemen are expensive, slow, and human errors prone.
Blockchain was first designed to exchange currency.
Nowadays it has many other uses such as managing loans, supporting all kinds of contracts, NFTs, Tokens, etc.

Satoshi Nakamoto (a collective or fake alias) released the First Blockchain proposition.
Bitcoin was the first blockchain implementation.
Blockchain technology was first designed for digital currency exchange.
Blockchain secures transactions in an not-trusted medium (the internet).

Transparency.
Decentralize trust and carry on distributed transactions and electronic commerce.
Remove man in the middle, merchant accounts, banks, clearing services.
Reduce charges and improve efficiency by removing the middle man.
Full auditability and transactions history.
No single point of failure.
We replicate the database in many places.
Most blockchains are public, tough transactions might be encrypted.

All new data is added, never removed, or replaced.
Blockchains are immutable databases on transactions.
Most traditional databases (relational, files, hierarchical, spreadsheet) can be overwritten.
Blockchain only allows CREATE and READ, No UPDATE or DELETE.
It is not a traditional CRUD.

To update a change, we need to add a new transaction at the end.
This is analogous to account ledgers.
Every Block has a group of transactions with (possible) different partners.
Blocks are chained like a linked list.
Since blockchain is immutable; stored data is available forever.
Blocks are replicated in nodes.
Nodes are replicated all over the net.
If we want to add new data, we need to reach a consensus.
All nodes have the same authority and a single vote.
We reach a Consensus once one of them gets (50% + 1) votes.
A Transaction can be anything as long as we can store it with bytes.
To transfer cryptocurrency we will add to the ledger a Transaction for an amount with source a destination addresses.

To make hash computation hard we need to introduce some random data with the transaction.
We force the hash value of the transactions + the fake data to have an arbitrary form.
We ask the computed hash function to have some leading zeroes.
At Bitcoin there are currently 19 zeroes.
The random data is called a Nonce.
We need a nonce such as, together with the valid transactions, it yields a hash with some leading zeroes.
It is very costly to search for this nonce.
Bitcoin uses leading zeroes. Other blockchain implementations use similar mechanisms.

Mining is the artificial process to find the proper Nonce to add to a group of transactions to achieve a hash with a fixed number of leading zeroes.
Mining takes a lot of computational time and energy.
Miners use specialized hardware where energy is cheap all over the world.
Nowadays, Mining is a threat to the environment.
Nodes compete for the price provided it is valuable.
The first one who solves the math puzzle gets the reward.
After global validation, new Bitcoins (or equivalent) are rewarded to the one who solves the puzzle.
Global validation is easy since hash encoding is cheap as opposed to hash decoding (mining).
The reward motivates miners to legitimize and monitor Blockchain transactions, ensuring their validity.

Blocks are added after consensus.
If 50% +1 agree to fake a chain, they can do it. This is known as the 51 % Attack
Proof of work is the most used mechanism and it consists of global hash validation.
Proof of Stake requires less computer power than Proof of work. it uses bet voting to select a winner.
Currently, there are no efficient ways to carry on Proof of Stake in a decentralized way.
There are several other alternatives.

Voilá.
This is basic Blockchain.
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