This document discusses the implementation of a blockchain in Scala. It begins with an overview of Bitcoin and the concepts of proof of work, mining, and nonce. It then shows code for implementing a basic blockchain in Scala, including a Block class with a hash and calculateHash method, and a Blockchain class to store the chain. Finally, it expands on this to include transactions in blocks and rewards for mining.

1. Scala
2018/11/10 Scala Summit 2018

2. • @itohiro73
• FOLIO
• Reladomo in Scala Scala
Summit 2017

4. • 2009 Satoshi Nakamoto
Bitcoin https://bitcoin.org/bitcoin.pdf
• Bitcoin
•
• 2017

5. •
•
•

9. 🙋

12. 👍

14. 0

15. 🤔

18. •
✓
• Proof of Work
✓
✓nonse Proof of Work
✓mining

20. •
•
•
•

21. import java.math.BigInteger
import java.security.MessageDigest
object HashFunction {
val MD_SHA256 = MessageDigest.getInstance("SHA-256")
def sha256(input: String): String =
{
String.format("%064x", new BigInteger(1,
MD_SHA256.digest(input.getBytes("UTF-8"))))
}
}

22. scala> HashFunction.sha256("a")
res0: String =
ca978112ca1bbdcafac231b39a23dc4da786eff8147c4e72b9807785
afee48bb
scala> HashFunction.sha256("test")
res1: String =
9f86d081884c7d659a2feaa0c55ad015a3bf4f1b2b0b822cd15d6c15
b0f00a08

23. scala> HashFunction.sha256("same input")
res2: String =
c2f991739d5824b4e1d8bafaffb735b9e4061f801d82c4aaf57aea02
495f750c
scala> HashFunction.sha256("same input")
res3: String =
c2f991739d5824b4e1d8bafaffb735b9e4061f801d82c4aaf57aea02
495f750c

24. ??? =
f0157537806d0ec6fd86455f6603bbaf1efed378798bcb43377456bc
6a8bfd78

25. scala> HashFunction.sha256("random input1")
res5: String =
3ef129a908f6b5e0c11cade17bb27691f6bd8cfffbb18622448a5fb229ca724d
scala> HashFunction.sha256("random input2")
res6: String =
dac708dccfe5ccbf009c9e5cd43ee9bf592abd0c7c04b421d8fe79f7518784c3
scala> HashFunction.sha256("random input3")
res7: String =
30b9b0875d568d926cf653f2360e95c86e8b798574a0ec95ceb7ef43cc9768ad

31. class Block(val timestamp: LocalDateTime, val data:
String, val previousHash: String) {
val hash = calculateHash()
def calculateHash(): String = {
val value = timestamp.toString + data + previousHash
HashFunction.sha256(value)
}
}

32. override def toString: String = {
"{ntTimestamp: " + this.timestamp +
"ntData: " + this.data +
"ntPrevious Hash: " + this.previousHash +
"ntHash:" + this.hash +
"n}"
}

33. class Blockchain(){
var chain = Seq[Block](createGenesisBlock())
def createGenesisBlock(): Block = {
new Block(LocalDateTime.now(), "A genesis block")
}
def addBlock(block: Block): Unit = {
this.chain = this.chain :+ block
}
def getLastBlock(): Block = {
this.chain.last
}
}

34. override def toString: String = {
this.chain.mkString("n")
}

35. def isChainValid(): Boolean = {
for(i <- 1 until this.chain.length) {
val currentBlock = this.chain(i)
val previousBlock = this.chain(i-1)
if(currentBlock.hash != currentBlock.calculateHash())
return false
if(currentBlock.previousHash != previousBlock.hash)
return false
}
return true
}

40. •Bitcoin Proof of
Work
•Proof of Work
0
✓ Satoshi Nakamoto

41. •
• nonce
• mining
• =difficulty
✓Bitcoin 10 difficulty

43. • nonce
• nonce

44. class Block(val timestamp: LocalDateTime, val data: String, val previousHash: String = "") {
var hash = calculateHash()
var nonce = 0
def calculateHash(): String = {
val value = timestamp.toString + data + previousHash + nonce
HashFunction.sha256(value)
}
def mineBlock(difficulty: Int): Unit = {
while(this.hash.substring(0, difficulty) != Array.fill(difficulty)("0").mkString ) {
this.nonce += 1
this.hash = calculateHash()
}
println("Block mined: " + this.hash)
}

45. class Blockchain {
var chain = Seq[Block](createGenesisBlock())
val difficulty = 4
def createGenesisBlock(): Block = {
new Block(LocalDateTime.now(), "A genesis block.")
}
def addBlock(block: Block): Unit = {
block.mineBlock(difficulty)
this.chain = this.chain :+ block
}

47. •nonce
Proof of Work
•Blockchain Block

56. class Transaction(val fromAddress: String, val
toAddress: String, val amount: Double) {
override def toString: String = {
"From Address: " + fromAddress + ", To Address: " +
toAddress + ", Amount: " + amount
}
}

57. import java.time.LocalDateTime
class Block(val timestamp: LocalDateTime, val transactions: Seq[Transaction], val previousHash: String = "") {
var hash = this.calculateHash()
var nonce = 0
def calculateHash(): String = {
val value = this.timestamp + this.transactions.mkString + this.previousHash + this.nonce
HashFunction.sha256(value)
}
def mineBlock(difficulty: Int): Unit = {
while(this.hash.substring(0, difficulty) != Array.fill(difficulty)("0").mkString) {
this.nonce += 1
this.hash = this.calculateHash()
}
}
override def toString: String = {
"{ntTimestamp: " + this.timestamp +
"ntTransaction: " + this.transactions.mkString("ntt{nttt", "nttt", "ntt}") +
"ntPrevious Hash: " + this.previousHash +
"ntHash: " + this.hash +
"ntNonse: " + this.nonce +
"n}"
}

58. class Blockchain {
var chain = Seq[Block](createGenesisBlock())
val difficulty = 4
var pendingTransactions = Seq[Transaction]()
val miningReward = 100
def createGenesisBlock(): Block = {
new Block(LocalDateTime.now(), Seq(new
Transaction("", "Initial Pool Address", 500)))
}

59. def addTransaction(transaction: Transaction): Unit = {
this.pendingTransactions = this.pendingTransactions :+ transaction
}
def minePendingTransactions(rewardAddress: String): Unit = {
val newBlock = new Block(LocalDateTime.now(), this.pendingTransactions)
newBlock.mineBlock(this.difficulty)
println("Block successfully mined: " + newBlock)
this.chain = this.chain :+ newBlock
this.pendingTransactions = Seq[Transaction](new Transaction("Reward",
rewardAddress, this.miningReward))
}

60. def getBalanceOfAddress(address: String): Double = {
var balance = 0.0
this.chain.flatMap(block =>
block.transactions).foreach(transaction => {
if(transaction.fromAddress == address)
balance -= transaction.amount
if(transaction.toAddress == address)
balance += transaction.amount
})
balance
}

63. •
✓
• Proof of Work
✓
✓nonse Proof of Work
✓mining

64. https://github.com/itohiro73/blockchain-scala

65. Satoshi Nakamoto (2009) Bitcoin: A Peer-to-Peer Electronic Cash System
2017
2018
Building a blockchain with Javascript