As soon as a new transaction is added, it is broadcasted to all the

nodes and the mining nodes start working to solve the proof-of-work

puzzle. Whosoever finishes it first, broadcasts it to the others. The

nodes accept the block only if all the transactions in it are valid and

not already spent. The transaction is confirmed and added to the

Blockchain only if a minimum percentage of all the nodes accept it.

For the Bitcoin, originally the percentage was 51%, matching the

democratic voting models in the world. However, soon it was

observed that more than 51% percent of the computing power in the

Bitcoin network lies with a handful of miners today.

51% attack is a well-known attack, especially in Bitcoin or any

other similar Blockchain network, where one or a group of nodes

try to take full control of the network by acquiring the ownership of

more than 50% of the nodes.

Hence, people soon tried to increase this consensus percentage

from 51% to a higher percentage. Ripple is another Blockchain

product that today uses an 80% consensus model.

Note, Bitcoin is not the only cryptocurrency that works on the Proof-

of-work consensus model; there are hundreds of others such as

Ethereum 1.0, Dogecoin, Litecoin, Bitcoin Cash, Ethereum Classic,

Monero etc.

A complete list of the PoW based Blockchain protocols can be found

at the following link: https://coinmarketcap.com/view/pow/

1.6.4 DAPPS

In the preceding example, we saw how the data or a block carrying

the transaction(s) are added to a Blockchain. But that’s not all. A

Blockchain works in the Decentralized mode and the technology is

known as DAPPS or Decentralized Applications. It’s implemented on

a network where every node keeps either a whole or a partial copy of

the Blockchain. This leads to a greater transparency and no single

point of failure for the transactions.

1.7 Threats & Challenges in Public Blockchains