intro-to-ethereum

## Contents
1. Special Thanks `3`
1. Foreword `4`
1. Bitcoin and The Blockchain `5`
    1. Bitcoin and the Double-Spending Problem `5`
    1. The Blockchain `7`
        1. Validating Transactions `8`
        1. Ordering Transactions `11`
            1. Physics to the Rescue `14`
        1. Definition `17`
    1. Example: a Perpetual Message System Using Webtasks and Bitcoin `20`
        1. The implementation `21`
            1. The /new endpoint `21`
            1. The /address endpoint `21`
            1. The /message endpoint `21`
            1. The /debugNew endpoint `22`
        1. The Code `22`
        1. Deploying the example `24`
    1. Summary `25`
2. Ethereum: a Programmable Blockchain `26`
    1. Introduction `26`
        1. Blockchain Recap `26`
    1. Ethereum: a Programmable Blockchain `28`
        1. Ether `31`
        1. Smart Contracts `31`
            1. State `32`
            1. History `35`
            1. Solidity and a Sample Smart Contract `36`
        1. Current and Potential Uses `37`
            1. The Decentralized Autonomous Organization (DAO) `38`
            1. A Central Bank or Your Own Coin `38`
            1. A Crowdfunding System `38`
            1. Prove That You Said Something in the Past `39`
            1. Proof of Existence for Digital Assets `39`
    1. Example: A Simple Login System using Ethereum `40`
        1. Running the Example `44`
            1. Get an Ethereum node client `44`
            1. Create a new Ethereum account to mine some Ether `44`
            1. Start mining some Ether `45`
            1. Compile and deploy our Login contract `45`
            1. Install an Ethereum wallet `46`
            1. Tell the Ethereum wallet of the contract `46`
            1. Deploy the backend `49`
            1. Serve the frontend `49`
            1. Test everything together! `50`
    1. Summary `50`
3. A Practical Authentication Solution for Ethereum Users `51`
    1. Introduction `51`
    1. Towards a Practical Authentication Solution for Ethereum Users `52`
    1. A Login System for Ethereum Users `53`
        1. Registration `57`
        1. Authentication `59`
        1. Cons `60`
    1. Try it out! `60`
        1. Get an Ethereum Wallet `61`
            1. Get Metamask `61`
            1. Create a New Account `61`
            1. Get Some Ether `61`
        1. Get the Mobile Authenticator App `62`
            1. Get the App `62`
            1. Register `62`
        1. Enable Your Ethereum Address for Logins `62`
            1. Get Your Mobile App (Secondary) Address `62`
            1. Call the Contract! `63`
        1. Login to Our Test Site `64`
        1. Explore the Code `64`
    1. Summary `65`


Ever wondered how blockchains work? Or how Bitcoin managed to change the landscape of monetary transactions? Or what's the magic behind Ethereum?
Then this e-book is for you. In it we delve into the development of blockchains: distributed, immutable, verifiable ledgers for transactions.
We explore how they became instrumental in the development of the first large-scale cryptocurrency, Bitcoin, and how its ideas were extended to give birth to Ethereum, a powerful blockchain that marries decentralized transactions with Turing-complete contracts.