A small task implementing the most basic principles of Blockchain technology
This small (ongoing) code is initially designed for demonstration purposes. A class of blocks is created, encompassing the most important attributes of a block: index, timestamp, the data contained, the previous hash string and of course, its own hash. For the hash generation, crypto-js library is used (function SHA25).
All blocks, including the first (genesis) block are set to have a hash which depends on the block's timestamp, among other attributes. That is equal to whatever date().getTime() function returns at the moment of each block's creation (which is equal to the number of miliseconds counting form 1970/01/01 until now).
There are functions for creating a new block given some input data (newBlock), for checking a potential new block with respect to the last block's index and hash (checkBlock) and finally for adding this block to the chain (addBlock). There are also functions to ensure that the chain is unaltered (checkChain) before proceeding with its update (updateChain). All of those functions are grouped together at the last part of the code.
Ten test blocks (of dummie input data) are added to the chain after the genesis block is created ("manually", using a fixed loop). Before each block's creation, the checkBlock function is called to determine the validity of the block, and before the chain is updated, the checkChain function scans the chain for inconsistencies. The indexes and hash strings of the blocks appear on the command prompt (of Node.js).
Alternating the data of an existing block should not be allowed. Using a replica of the blockchain ("testchain") and changing a random block's data, leads to a different hash of the block and checkChain function creates an error, as it should. This stops a possible attempt to harm the blockchain once created.
- A web server, so there can be user interaction with the chain
- Some simple Proof of Work attribute
- Some sort of meaningful input data to the blocks