Una Blockchain (in italiano letteralmente: catena di blocchi) è una base di dati distribuita, introdotta dalla valuta Bitcoin che mantiene in modo continuo una lista crescente di record, i quali fanno riferimento a record precedenti presenti nella lista stessa ed è resistente a manomissioni. La prima e più conosciuta applicazione della tecnologia blockchain è la visione pubblica delle transazioni per i bitcoin, che è stata ispirazione per altre criptovalute e progetti di database distribuiti


Blockchain, What is it ?

Bank note

Serial number 

is the


The bank network

It is centralised

The bitcoin network

Peer-to-peer system with no third party

The Peer-to-Peer network

1 computer/user = 1 node

1. Immediate propagation of the information between all of the nodes of the network

2. The information is encrypted and private

1. The network is thus DECENTRALISED

2. If a new node enters the network, it receives a copy of all the information of the network (No point of failure)

3. The database is DISTRIBUTED

Symetric encryption

Encryption key


Decryption key

Asymetric encryption

Encryption key

different from

Decryption key

Permits to send coded messages

Digital Signature

Impossible to falsify Impossible to repudiate

Why is it called a "blockchain" ?

1. The next blocks contains transactions

2. The transations contains encrypted information

==> All these transactions constitue a "ledger"

The Hash

The block name is called a  "hash"

The Hash of the block N+1 includes the ID of the previous block

A major issue

The candidate systems to E-cash suffer from the following fact:


The rational economic behavior is to attack the bank...

...which centralizes power and weaknesses

Bitcoin: changing the target

(Nakamoto, 2008)

The rational economic behavior to get its blocks approved is to strictly follow the procedure

Therefore, the attackers should reinforce the system.
A central authority would not be needed anymore 

The Byzantine generals (Bitcoin version)

Likewise, Bitcoin is a bet on the next step

The first right bettor earns Bitcoins

Either you bet like the others and you have a chance or you don't and you won't have a chance.

What the others will vote for is ignored

Bitcoin is basically a vote for History

The 50% rule


A necessary but not sufficient condition to control to control the system is to have more than 50% of the bets


More than 80% of the minors (in compute capacity) are behind the gread firewall of china (Antpool, and others)

Proof of Work (PoW)

A good PoW is:

- Hard to obtain (roughly every 10 minutes)

- Easy to verify (0.01 seconds)

Objective 1: there is the time to bet on 1 block at a time

How is the bet retained?

Once the PoW is done, it is spread out then verified

If the block is approved, it is added to History

The next blocks start from the new added block

If several PoW are submitted, the most work-consuming one is selected - assuming that it corresponds to the oldest bet)

In other words, calculation time (i.e. electricity)is invested. It is a race!

How to earn Bitcoins?

2 ways:

- Get money from transfers

- By mining (getting blocks approved)

Anyone can do both !

Mining makes the system protected from changes. It is also the most profitable way, thus the most rational choice

Let's sum up

Proof of work protects the integrity of History

The earnings leads the minors to reinforce the system

History is made by successive bets trough power (compute)

History is know by everybody


Use cases

Smart contracts

Banks : fundraisings

Bitnation : The case of Estonia

Video to watch

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DLCI Blockchain

by guillaumecotenceau


Public - 9/14/16, 8:33 AM