The Blockchain and JavaScript

Portia Burton@pkafei

Node.js Interactive

Who am I?My name is Portia Burton

I am a full-stack developer at the Atlantic magazine

Became interested in blockchains earlier this year

Not a cryptographic expert

Background about Blockchain and Bitcoin

What is a Blockchain?

A blockchain is a cross between a decentralized data store and bittorrent. It is similar to a database but there isn’t a database administrator.

What is Bitcoin?Type of Cryptocurrency

Creation based on paper by Satoshi Nakamoto titled “Bitcoin: Peer-to-Peer Electronic Cash System”

Peer-to-peer which means transactions happen without a third party. Alice can send money directly to Bob

Bitcoin vs. BlockchainBitcoin is part of a blockchain

Blockchain is a digital ledger of transactions

Each transaction is cryptographically signed

Blockchains are trustless

The bitcoin blockchain is open to everyone

We will focus on the Blockchain

Can an average developer build blockchain applications?

Yes, We Can!

But first, some more background

Many Different Types of Cryptocurrencies

Ethereum

Introduction to EthereumEthereum is a programmable blockchain, every new blockchain

spawned from Ethereum has the same properties as Ethereum

Ethereum Virtual Machine is the low level machine language

Is Turing complete, unlike bitcoin which does not have looping capabilities

It also is aware of multiple states, unlike bitcoin which is only aware of two states (spent and unspent)

Different Consensus MechanismsProof of Work: Uses the Etash algorithm. The Etash algorithm is based on Bitcoin’s the Dagger-Hashimoto algorithm. ⛏⛓

Proof of Stake: Proof of Stake is another way of validating. It calculates the weight of the node, being proportional to its computational resources. It’s less resource intensive than Proof of Work.

Smart Contracts

What is a Smart Contract?Stored on the blockchain and

executed by code

Many smart contracts are written in Solidity (syntax is similar to JavaScript)

Powered by gas which can be computationally mined or purchased in an exchange

People and machines can interact with it

Transaction: Signed data package that stores a message to be sent from an externally owned account

GAS: the name for the execution fee that senders of transactions need to pay for operations on Ethereum blockchain

VALUE (field): The amount of wei to transfer from sender to the recipient

STARTGAS (value): Representing the maximum number of computational steps the transaction execution is allowed to take

GASPRICE (value): Representing the fee the sender is willing to pay for gas

Applications of Ethereum Blockchain of Smart Contracts

Self-executing legal contracts

Create “American Idol” where people can vote using generated tokens

Company boards can be ran virtually

Dropbox business model create and sell encrypted storage space

Predicting financial futures based on an oracle

Ethereum Chains

Different BlockchainsPublic blockchain: It is the official Ethereum chain that everyone can read and interact with

Testnet blockchain: The official test chain of Ethereum. Good way to test contracts without wasting real ether

Private blockchain: This is a blockchain that you can create yourself. This blockchain can be freely accessed by others, or you can add addresses by invite only

How to build a custom blockchain?1.Create a Genesis file

2.Init your blockchain locally on the command line*

3.Start your chain again, this time with parameters (not in the documentation)

*Be sure to run “init” each time

Genesis FileNonce: a random or pseudo-random number that can only be used once

gasLimit: is the highest amount you are willing to pay for a computation

Alloc: how much money that you allocate to your blockchain

{

"nonce": "0x0000000000000042", "timestamp":

"0x0",

"parentHash":

"0x0000000000000000000000000000000000000000000000000000

000000000000",

"extraData": "0x0", "gasLimit": "0x8000000",

"difficulty": "0x400",

"mixhash":

"0x0000000000000000000000000000000000000000000000000000

000000000000",

"coinbase":

"0x3333333333333333333333333333333333333333",

"alloc": { }

}

CustomGenesis.json

Private Blockchain ParametersUse these parameters in the cli when creating a custom blockchain

Nodiscover: Other people will not discover your blockchain

RPC: JS interface for your node

Networkid: Create a custom networkid inter

geth --identity "Testing" --rpc --rpcport "8080" --rpccorsdomain "*" --datadir "C:\chains\TestChain1" --port "30303" --nodiscover --rpcapi "db,eth,net,web3" --networkid 1999 console

In Conclusion

Combine Mist and EthereumDownload Mist

https://github.com/ethereum/mist

Download Democracy Contract:

https://www.ethereum.org/dao

Blockchain Technology Growing PainsForces different parties (or contractors) to be savy about code

Still very new platform and technology

Solidity Contract BugsTransaction-Ordering Bug (TOD): Smart contract assumes a particular state of a contract that doesn’t exist

Timestamp Dependence Bug: Asynchronous network is disconnected from a synchronized global clock. Some contracts assume that network is on global contract

Unchecked Send: Most common exploit. Attacker elicits unexpected behavior from the contract by calling if from a carefully constructed call-stack

Smart Contract Bloopers

https://ethereum.karalabe.com/talks/2016-hackethon.html#1

Enough About Me: How can you get started today?Solidity Tutorial: https://solidity.readthedocs.io/en/develop/

Bootstrap Meteor App: https://github.com/SilentCicero/meteor-dapp-boilerplate

Example Dapps: http://ethereum.stackexchange.com/questions/2940/where-can-i-find-some-solidity-smart-contract-source-code-examples

Command Line Interface of Interacting with the Ethereum Network: https://www.ethereum.org/cli

Meteor: https://www.meteor.com/

Different Ethereum FrameworksThese frameworks provide developers the tools need to create, test, and deploy smart contracts using Ethereum

Truffle: https://github.com/ConsenSys/truffle

The Dao: https://github.com/slockit/DAO

Embark: https://github.com/iurimatias/embark-framework

Thank You!

References1.http://ethdocs.org/en/latest/mining.html#what-is-mining

2.http://ethdocs.org/en/latest/frequently-asked-questions/frequently-asked-questions.html#what-s-the-difference-between-account-and-wallet-contract

3.http://www.coindesk.com/making-sense-smart-contracts/

4.https://github.com/ethereum/go-ethereum/wiki/Command-Line-Options

5.http://www.ethdocs.org/en/latest/contracts-and-transactions/account-types-gas-and-transactions.html

6.https://blog.ethereum.org/2016/07/12/build-server-less-applications-mist/