There are majorly three technologies which create a blockchain when combined. The fascinating part here is, all of those exist even before Blockchain was a concept.

1.Distributed Ledger Technology (A Peer-to-Peer System, for record keeping)

2.Cryptography (Public Key, for identity storage)

3.Network Servicing Program or Protocol (For record-keeping and security services in the network's transactions, an incentive is offered.)

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Let's understand each of them one by one in brief:

1.Distributed Ledger Technology: Distributed Ledger Technology (DLT) is a digital system in which the records of transactions and their details are created at the same time at multiple locations or places so every record-keeper has the same copy of the transaction which keeps the system transparent.

2. Cryptography: The key purpose of this component of blockchain technology is creation of secure reference for digital identity. The identity is entirely based on the possession of a combination of private and public cryptographic keys. These keys when combined can be clearly seen as a masterly form of assent, creating a very useful digital signature.In succession, this digital signature gives a very strong ownership control.

3.Network Servicing Program or Protocol: This is about you offering the processing power of your computer as a service to the blockchain network. On doing so, one of the computers is rewarded. The self-interest of a person becomes useful in helping to service the need of public. Bitcoin network is the best example to understand this. The miners get the reward for their work.
Source: http://techcryptoguru.com/?p=526

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