Within this post some of the teaching programming examples used in the class and the logic behind them will be discussed. Health warning: These are simple examples; only meant to get some basic ideas across that the students can then build on.
1. Javascript version
This section looks at a producing a blockchain on a local machine - to build up the ideas gradually. Confession time, my starting point was the fantastic videos shown below from Simply Explained -Savjee - really nice introduction.
So as in the video Visual Studio Code was used to develop the solution; using JavaScript and running Node.js - a little bit of setting up is needed but certainly on a Mac or Linux machine it wasn't too difficult. So the code was built up and the following produced.
//adapted from the videos of Simple Explained -Savjee
//https://www.youtube.com/channel/UCnxrdFPXJMeHru_b4Q_vTPQ
const SHA256 =require('crypto-js/sha256');
class Block{
constructor (index,timestamp, data, previousHash = ''){
this.index = index;
this.timestamp = timestamp;
this.data = data;
this.previousHash = previousHash;
this.hash = this.calcHash();
this.nonce =0;
}
calcHash(){
return SHA256(this.index+this.previousHash+this.timestamp+JSON.stringify(this.data)+this.nonce).toString();
}
mineBlock(difficulty){
while(this.hash.substring(0,difficulty) != Array(difficulty+1).join("0")){
this.nonce++;
this.hash = this.calcHash();
}
console.log("Block mined hash: "+ this.hash);
}
}
class Blockchain{
constructor(){
this.chain = [this.createGenesisBlock()];
this.difficulty = 4;
}
createGenesisBlock(){
return new Block("0","13/3/2017","Start","0");
}
getLatestBlock(){
return this.chain[this.chain.length-1];
}
addBlock(newBlock){
newBlock.previousHash=this.getLatestBlock().hash;
newBlock.mineBlock(this.difficulty);
this.chain.push(newBlock);
}
isChainValidOne(){
for (let loop=1; loop<this.chain.length; loop++){
const current = this.chain[loop];
const prevOne = this.chain[loop-1];
if((current.hash != current.calcHash())||(current.previousHash != prevOne.hash)){
return false;
}
}
return true;
}
}
let educoin = new Blockchain();
educoin.addBlock(new Block(1,"10/7/2018", {name : "Ali", qual : "PhD", qual1 : "BSc"}));
educoin.addBlock(new Block(2,"10/7/2018", {name : "Scott", qual : "PhD"}));
educoin.addBlock(new Block(3,"10/4/2018", {name : "Scott", qual1 : "Swimming Certificate"}));
console.log(JSON.stringify(educoin,null,4));
console.log("Is the chain valid ? "+educoin.isChainValidOne().toString());
The idea of going down this route was the students are familiar with JavaScript so it follows on from what they know; promotes the idea that blockchains are not language specific and lastly the elements of the block and blockchain can be seen - without the language getting 'clever' and hiding how it is done.
2. Solidity
The second stage was build up an example to go onto the Ethereum blockchain. So I decide to show Solidity, which is a programming language for doing this. After experimenting with various options I decided to use the free (always good) online integrated environment from Ethereum called Remix (http://remix.ethereum.org/) and stick with the online version. Remix meant that there wasn't any extra installation, it is pretty self-contained and it comes from Ethereum itself.
So the code produced is inspired by the #BlockchainEducationalPassport (https://blockchainedupass.uniteideas.spigit.com/Page/Home) project - but much simpler. The code sets up a record for a student (name and qualification) and adds it to a list/array of students.
pragma solidity ^0.4.0;
contract educoin1 {
struct edRec {
string name;
string qual;
}
address public student;
mapping (address => edRec) public Students;
address[] studentsByAddress;
function add(string _student, string _qual) public {
address thisAddress=msg.sender;
Students[thisAddress].name = _student;
Students[thisAddress].qual=_qual;
studentsByAddress.push(thisAddress);
}
}
The figures below show a 'record' being added (figure 1) and then looking at waht is stored (figure 2)
 |
| Figure 1: Entering the record |
 |
| Figure 2: Seeing the transactions |
3. Where next
The final section was to look at Distributed Ledger alternatives to Blockchain - but not the programming them so the Tangle used in IOTA https://www.iota.org/get-started/what-is-iota was discussed.
All views are the authors, and may not reflect the views of any organisation the author is connected with in any way.
