Blockchain is a system of recording information in a way that makes it difficult or impossible to change, hack, or cheat the system. A blockchain is essentially a digital ledger of transactions that is duplicated and distributed across the entire network of computer systems on the blockchain.

1. LESSON 3
1- Transparency in Blockchain?
2- Is Blockchain Secure?
3- Bitcoin VS Blockchain.

2. TRANSPARENCY IN BLOCKCHAIN
Because of the decentralized nature of Bitcoin’s blockchain, all
transactions can be transparently viewed by either having a
personal node or using blockchain explorers that allow anyone
to see transactions occurring live.
Each node has its own copy of the chain that gets updated as
fresh blocks are confirmed and added.
This means that if you wanted to, you could track Bitcoin
wherever it goes.
For example, exchanges have been hacked in the past,
where those who kept Bitcoin on the exchange lost everything.

3. While the hacker may be entirely anonymous, the Bitcoins
that they extracted are easily traceable.
If the Bitcoins stolen in some of these hacks were to be moved
or spent somewhere, it would be known.
Of course, the records stored in the Bitcoin blockchain
(as well as most others) are encrypted.
This means that only the owner of a record can decrypt it to
reveal their identity (using a public-private key pair).
As a result, users of blockchains can remain anonymous
while preserving transparency.

4. Is Blockchain Secure?
Blockchain technology achieves decentralized security and trust
in several ways. To begin with, new blocks are always stored linearly
and chronologically. That is, they are always added to the “end” of the
blockchain.
After a block has been added to the end of the blockchain, it is
extremely difficult to go back and alter the contents of the block
unless a majority of the network has reached a consensus to do so.
That’s because each block contains its own hash, along with the
hash of the block before it, as well as the previously mentioned
time stamp. Hash codes are created by a mathematical function
that turns digital information into a string of numbers and letters.
If that information is edited in any way, then the hash code
changes as well.

5. Let’s say that a hacker, who also runs a node on a blockchain network,
wants to alter a blockchain and steal cryptocurrency from everyone
else. If they were to alter their own single copy, it would no longer
align with everyone else’s copy.
When everyone else cross-references their copies against each other,
they would see this one copy stand out, and that hacker’s version of
the chain would be cast away as illegitimate.
Succeeding with such a hack would require that the hacker
simultaneously control and alter 51% or more of the copies of
the blockchain so that their new copy becomes the majority copy
and, thus, the agreed-upon chain. Such an attack would also
require an immense amount of money and resources, as they
would need to redo all of the blocks because they would now
have different time stamps and hash codes.

6. Due to the size of many cryptocurrency networks and how fast they
are growing, the cost to pull off such a feat probably would be
insurmountable. This would be not only extremely expensive
but also likely fruitless.
Doing such a thing would not go unnoticed, as network members
would see such drastic alterations to the blockchain.
The network members would then hard fork off to a new version of
the chain that has not been affected.
This would cause the attacked version of the token to plummet in
value, making the attack ultimately pointless, as the bad actor has
control of a worthless asset. The same would occur if the bad
actor were to attack the new fork of Bitcoin.
It is built this way so that taking part in the network is far more
economically incentivized than attacking it.

7. Bitcoin VS Blockchain
Blockchain technology was first outlined in 1991 by Stuart Haber
and W. Scott Stornetta, two researchers who wanted to implement
a system where document time stamps could not be tampered with.
But it wasn’t until almost two decades later, with the launch of
Bitcoin in January 2009, that blockchain had its first real-world
application.
The Bitcoin protocol is built on a blockchain. In a research paper
introducing the digital currency, Bitcoin’s pseudonymous creator,
Satoshi Nakamoto, referred to it as “a new electronic cash system
that’s fully peer-to-peer, with no trusted third party.”

8. The key thing to understand here is that Bitcoin merely uses
blockchain as a means to transparently record a ledger of payments,
but blockchain can, in theory, be used to immutably record any
number of data points. As discussed above, this could be in the
form of transactions, votes in an election, product inventories,
state identifications, deeds to homes, and much more.
Currently, tens of thousands of projects are looking to implement
blockchains in a variety of ways to help society other than just
recording transactions—for example, as a way to vote securely
in democratic elections. The nature of blockchain’s immutability
means that fraudulent voting would become far more difficult to
occur.

9. For example, a voting system could work such that each
citizen of a country would be issued a single cryptocurrency or
token. Each candidate would then be given a specific wallet
address, and the voters would send their token or crypto to
the address of whichever candidate for whom they wish to vote.
The transparent and traceable nature of blockchain would eliminate
both the need for human vote counting and the ability of bad actors
to tamper with physical ballots.