Blockchain are realized by combining multiple technologies such as “P2P network", “consensus algorithm", “smart contract", “anti-counterfeiting / encryption technology".
In the Blockchain, we store transaction that occurred in the network in a chunk of records called “blocks". Besides transaction records, each block stores information called a hash value indicating the contents of the block that was generated immediately before※. The data structure in which the generated blocks are connected chronologically is exactly called a Blockchain.
If the attempt to tamper with the information in the block generated in the past is made, the hash value calculated from the changed block is different from the previous one, so the hash value of all subsequent blocks must be changed either. Such changes are practically difficult. In this way, the Blockchain has a data structure with excellent tamper resistance, which is a major feature.
※ What is a hash value?
The hash value is the data that compactly contains a certain amount of information calculated by algorithm (hash calculation). If the information is altered, the calculated hash value will be completely different.
The Blockchain has a mechanism to prevent tampering with not only the data structure but also data management methods. Although it is called “distributed ledger", the Blockchain has a role as a “ledger" to record all transactions occurring in the network, and all users participating in the network share the same “ledger", so the authenticity of information is ensured.
In addition, Blockchain are realized by combining multiple technologies such as “P2P network”, “consensus algorithm", “smart contract", “anti-counterfeiting / encryption technology".
"Smart Contract" is a mechanism that programs and executes contract performance automatically. A Smart Contract is an agent program that runs on a Blockchain, and it is possible to describe various businesses processing such as performing a contract if it meets certain conditions (the degree of feasibility depends on the Blockchain base).
In Blockchain, we use electronic signatures by public key cryptography technology to realize secure transactions with other parties, transparency and privacy protection of transactions by sharing ledger information.
In Blockchain there is no centralized administrator, the ledger information is shared with everyone on the network, and thus an overall consensus is formed. The way to do such a consensus is the “consensus algorithm". There are several consensus algorithms, such as Proof of Work (PoW) used for bit coins and Byzantine Fault Tolerance (PBFT) used for Hyperledger Fabric etc.
P2P network is responsible for data management of Blockchain. Unlike the client-server type, in P2P network there is no specific server or client, terminals, called nodes, are directly communicating each other and therefore information or settlement can be exchanged between users.