Welcome to the newline guide to privacy on blockchains, In this course we are going to be looking at privacy techniques used in blockchain and implementing really cool games like _Rock, Paper, Scissors_ on Ethereum and using cryptography primitives to help us improve privacy for our own applications.

Interested about building decentralized applications?

Want to learn how to store sensitive data in public chain or database?

Want to learn how privacy focussed cryptocurrencies actually keep transactions private?

Want to know all the tools of cryptography that you can use today?

Privacy is a very important concept in blockchains, writing a smart contract is one thing, but designing the privacy aspects of your application is another, using cryptography as a toolbox can be a way to achieve privacy that can yield very good results. For example, hashes with salt has been used for a long time to store user passwords without actually knowing the user passwords and even if the security gets compromised and they are stolen, no user data can be accessed by using the hash without knowing the preimage of the hash.

Privacy is at the heart of blockchains. Blockchains such as Bitcoin and Ethereum are very public by nature, to use them for your applications, you must not put any sensitive data on them, but you have to put something so at a later date, you can prove that a supply chain holds or a product is legitimate, but how do you go about putting data on blockchains without really revealing what the data is?

In this course we'll look at the various privacy technologies and then implement a simple but nuanced game in Solidity: _Rock, Paper, Scissors_. This game will give us a hands-on lesson in creating real-world applications that handle private data on a public blockchain.

Understand Privacy on Ethereum and Build Rock, Paper, Scissors with Solidity

In this course, we'll show you how to implement privacy in your applications and build fun projects like rock paper scissors

newline's Introduction to Privacy on Ethereum

---
title: Using Randomness to give privacy to users moves
slug: using-randomness-to-give-privacy
privateVideoUrl: https://fullstack.wistia.com/medias/whbfp2v8va
isPublicLesson: true
---

Using Randomness to hide users moves, can you figure it out? Have a go at it and see if you can implement it and I will talk about the solution with you here.

The solution is shown below so only look if you have had a go at solving it yourself and make sure to watch the video first

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```javascript { actualFilename=./protected/src/game.sol endChar=1573 endLine=53 startChar=0 startLine=1 statedFilename=server/index.js url=https&#x3A;//gitlab.com/fullstackio/books/newline-guide-to-privacy-on-blockchains/module_04/lesson_04.09/protected/src/game.sol }
pragma solidity 0.6.0;

contract Game {
    bytes32 constant ROCK = "ROCK";
    bytes32 constant PAPER = "PAPER";
    bytes32 constant SCISSORS = "SCISSORS";