Intro to the course

Introduction to the module

Introduction to Privacy

What is a blockchain

What is mining in blockchain?

What is privacy within blockchains

Why is Privacy important - Bitcoin?

Why is Privacy important - Ethereum?

Will Quantum computing break privacy?

Understanding Blockchains, Mining, and the Problem of Privacy

A brief look at privacy techniques in blockchains

ZCash

Moneoro

Coinjoin

Dash

Payment Channels

Stealth Address

Privacy Techniques in Various Blockchains

Implementing a rock paper scissors game

Setting up an environment for smart contract

Writing our first smart contract

Implementing Rock Paper Scissors

Deploying the contract and playing rock paper scissor on blockchain.

Problems with current implementation

Implementing privacy on the smart contract

Implementing A Basic Rock Paper Scissors on Ethereum

A twist in rock paper scissors game

Using Randomness to give privacy to users moves

A Walkthrough of the Solution

Conclusion and wrapping up rock paper scissors game

Implementing Privacy for Rock Paper Scissors on Ethereum

solidity

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

Building rock paper scissors on Ethereum using Solidity

How privacy focussed Blockchains work like ZCash, Monero, and more

How to implement rock paper scissors with complete privacy

Learn about cryptography primitives and how to use them

How to hide data within public Blockchains

When does privacy break and looking into Post-Quantum Cryptography

In this lesson we will walkthrough the solution and discuss the improvements/extensions that can be made to the implementation

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

pragma solidity 0.6.0;

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

    mapping(address => bytes32) public choices;

    function play(bytes32 choice) external {
        require(choices[msg.sender] == bytes32(0)); // make sure player hasnt played before
        choices[msg.sender] = choice;
    }

    function evaluate(
        address alice,
        bytes32 aliceChoice,
        bytes32 aliceRandomness,
        address bob,
        bytes32 bobChoice,
        bytes32 bobRandomness
    ) external view returns (address) {
        // make sure the commitment of the choices hold
        require(
            keccak256(abi.encodePacked(aliceChoice, aliceRandomness)) ==
                choices[alice]
        );

        require(
            keccak256(abi.encodePacked(bobChoice, bobRandomness)) ==
                choices[bob]
        );

        if (aliceChoice == bobChoice) {
            return address(0);
        }

        if (aliceChoice == ROCK && bobChoice == PAPER) {
            return bob;
        } else if (bobChoice == ROCK && aliceChoice == PAPER) {
            return alice;
        } else if (aliceChoice == SCISSORS && bobChoice == PAPER) {
            return alice;
        } else if (bobChoice == SCISSORS && aliceChoice == PAPER) {
            return bob;
        } else if (aliceChoice == ROCK && bobChoice == SCISSORS) {
            return alice;
        } else if (bobChoice == ROCK && aliceChoice == SCISSORS) {
            return bob;
        }
    }
}

---
title: A Walkthrough of the Solution
slug: a-walkthrough-of-solution
privateVideoUrl: https://fullstack.wistia.com/medias/yascbmem8p
isPublicLesson: true
---

In this lesson we will walkthrough the solution and discuss the improvements/extensions that can be made to the implementation

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

.  
..  
...  
....  
.....  
......  
.......  
........  
.........  
..........

```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_03/lesson_01.10/protected/src/game.sol }
pragma solidity 0.6.0;

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

    mapping(address => bytes32) public choices;

    function play(bytes32 choice) external {
        require(choices[msg.sender] == bytes32(0)); // make sure player hasnt played before
        choices[msg.sender] = choice;
    }

    function evaluate(
        address alice,
        bytes32 aliceChoice,
        bytes32 aliceRandomness,
        address bob,
        bytes32 bobChoice,
        bytes32 bobRandomness
    ) external view returns (address) {
        // make sure the commitment of the choices hold
        require(
            keccak256(abi.encodePacked(aliceChoice, aliceRandomness)) ==
                choices[alice]
        );

        require(
            keccak256(abi.encodePacked(bobChoice, bobRandomness)) ==
                choices[bob]
        );

        if (aliceChoice == bobChoice) {
            return address(0);
        }

        if (aliceChoice == ROCK && bobChoice == PAPER) {
            return bob;
        } else if (bobChoice == ROCK && aliceChoice == PAPER) {
            return alice;
        } else if (aliceChoice == SCISSORS && bobChoice == PAPER) {
            return alice;
        } else if (bobChoice == SCISSORS && aliceChoice == PAPER) {
            return bob;
        } else if (aliceChoice == ROCK && bobChoice == SCISSORS) {
            return alice;
        } else if (bobChoice == ROCK && aliceChoice == SCISSORS) {
            return bob;
        }
    }
}
```


I was not able to interact with the contract.I called the function play using Alice's account. I passed "ROCK" as the argument. However, I got the following error: Error encoding arguments: Error: invalid arrayify value (argument="value", value="ROCK", code=INVALID_ARGUMENT, version=bytes/5.4.0) I assume that the function play is expecting a bytes32 type of argument. Asumming that I am able to convert "ROCK" to bytes32, which is only possible using assembly, I am storing the bytes32 version of "ROCK" in storage, which conflicts with the following point.When the evaluate function is called, the require checks wether the bytes32 version of "ROCK" (from point 1) equales to the randomized hashed of "ROCK". However, these two will never be the same because when "ROCK" was saved in storage through the play function, it never knew the random element introduced in the hash function (through evaluate).The only way I can see this to work is that from the front-end, the play function should call keccak256(abi.encodePacked("ROCK", aliceRandomness)). By doing that, the randomized hashed of "ROCK" will be stored and used for later comparisons. Please, could you clarify these two points and the logic at the front-end? THanks a lot! 

Yeah it's very confusing that he's not clarifying how to pass in the choice to play. This is a key detail in understanding what he's doing.

tymicruz

What does the choice look like when using the play function in the more secure version of the code? I'm assuming that Alice and Bob have to do the keccak256 hash on their randomness and choice in the client? 

Would this randomness need to depend on client storage/web2.0 storage?  

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newline's Introduction to Privacy on Ethereum

WELCOMEIntroduction

Introduction:

Start Here

Module 1: Understanding Blockchains, Mining, and the Problem of Privacy

Introduction: (3:08)

Intro to the course

Introduction: (1:29)

Introduction to the module

Introduction: (4:13)

Introduction to Privacy

Lesson 1: (2:49)

What is a blockchain

Introduction: (4:38)

What is mining in blockchain?

Lesson 2: (3:23)

What is mining in blockchain?

Lesson 3: (2:13)

What is privacy within blockchains

Lesson 4: (4:22)

Why is Privacy important - Bitcoin?

Lesson 5: (2:44)

Why is Privacy important - Ethereum?

Lesson 6: (1:49)

Will Quantum computing break privacy?

Module 2: Privacy Techniques in Various Blockchains

Lesson 1: (1:04)

A brief look at privacy techniques in blockchains

Lesson 2: (2:15)

ZCash

Lesson 3: (2:35)

Moneoro

Lesson 4: (2:33)

Coinjoin

Lesson 5: (2:02)

Dash

Lesson 6: (2:59)

Payment Channels

Lesson 7: (1:04)

Stealth Address

Module 3: Implementing A Basic Rock Paper Scissors on Ethereum

Lesson 1: (1:40)

Implementing a rock paper scissors game

Lesson 2: (5:43)

Setting up an environment for smart contract

Lesson 3: (6:35)

Writing our first smart contract

Lesson 4: (8:29)

Implementing Rock Paper Scissors

Lesson 5: (3:27)

Deploying the contract and playing rock paper scissor on blockchain.

Lesson 6: (1:41)

Problems with current implementation

Lesson 7: (3:51)

Implementing privacy on the smart contract

Module 4: Implementing Privacy for Rock Paper Scissors on Ethereum

Lesson 1: (2:48)

A twist in rock paper scissors game

Lesson 2: (11:41)

Using Randomness to give privacy to users moves

Lesson 3: (2:26)

A Walkthrough of the Solution

Lesson 4: (4:02)

Conclusion and wrapping up rock paper scissors game

A Walkthrough of the Solution