CPSC 5910�Blockchain Security�Winter 2022��Session 09

Dr. Christian Seifert

cseifert@seattleu.edu

Outline for Today

• CPSC 5011: Object-Oriented Concepts

• Assignment 4 Questions?
• Solidity Programming 102
• Storage Slots
• Proxy Pattern
• Introduction to Development Env 
• Remix
• Brownie
• Tenderly
• Deploying, testing and interacting with your first smart contract using Remix

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Page 2

Storage Slots

• 32 byte storage slots
• Starts at slot 0
• There are 2^256-1 slots available

Page 3

Storage Slot – Value Types

contract StorageLayout {

uint256 public id = 543;

}

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Storage slot 0: 543

w3.eth.get_storage_at("0xc145718228438a045d76d11248fb779e4d23f942", 0)

-> 0x000000000000000000000000000000000000000000000000000000000000021f

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Would this work if the id would be private?

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https://coinsbench.com/solidity-layout-and-access-of-storage-variables-simply-explained-1ce964d7c738

Page 4

Storage Slot Packing

pragma solidity ^0.8.16;

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contract StorageLayout {

uint64 public value1 = 1;

uint64 public value2 = 2;

uint64 public value3 = 3;

uint64 public value4 = 4;

uint256 public value5 = 5;

}

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web3.eth.getStorageAt("0x9168fBa74ADA0EB1DA81b8E9AeB88b083b42eBB4", 0)

-> 0x0000000000000004000000000000000300000000000000020000000000000001

web3.eth.getStorageAt("0x9168fBa74ADA0EB1DA81b8E9AeB88b083b42eBB4", 1)

-> 0x0000000000000000000000000000000000000000000000000000000000000005

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Order matters! What if we swap value 5 with value 3?

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Page 5

Storage Slot – Arrays

contract StorageLayout {

uint256[] public values = [1,2,3,4,5,6,7,8];

}

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1. Find where the array is stored:

keccak256 of the storage slot (e.g. 0)

-> 0x290decd9548b62a8d60345a988386fc84ba6bc95484008f6362f93160ef3e563

2. Add the element index to access the specific element

e.g. index 1

-> 0x290decd9548b62a8d60345a988386fc84ba6bc95484008f6362f93160ef3e564

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web3.eth.getStorageAt("0x9168fBa74ADA0EB1DA81b8E9AeB88b083b42eBB4", “0x290decd9548b62a8d60345a988386fc84ba6bc95484008f6362f93160ef3e564”)

-> 0x0000000000000000000000000000000000000000000000000000000000000002

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Page 6

Storage Slot – Mappings

contract StorageLayout {

mapping(address => uint) public balances;

constructor() {

balances[0x6827b8f6cc60497d9bf5210d602C0EcaFDF7C405] = 678;

balances[0x66B0b1d2930059407DcC30F1A2305435fc37315E] = 501;

balances[0x9Edc86C3BAe6B04Ce2ea8EFF3abAC0C3160ba243] = 321;

}

}

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1. Calculate the kaccak of the concatenated padded value and padded storage slot

e.g. 0000000000000000000000006827b8f6cc60497d9bf5210d602c0ecafdf7c405

0000000000000000000000000000000000000000000000000000000000000000

-> 86dfc0930cb222883cc0138873d68c1c9864fc2fe59d208c17f3484f489bef04

2. web3.eth.getStorageAt("0x59580A79b12Df8A1763ED2e43C35ef700d20580E", "0x86dfc0930cb222883cc0138873d68c1c9864fc2fe59d208c17f3484f489bef04")

-> 0x00000000000000000000000000000000000000000000000000000000000002a6 (678)

Page 7

Storage slot collisions

https://mixbytes.io/blog/collisions-solidity-storage-layouts

Page 8

Proxy Pattern

Contracts are immutable, which makes upgrades and bug fixes impossible. Industry has adopted proxy pattern to create upgradable smart contracts.

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Page 9

Proxy Contract

setImpl(addr)

functionA()

functionB()

Impl 1

functionA()

functionB()

Impl 1.1

functionA()

functionB()

Remix

Intro to Remix

Page 10

Brownie

• Intro to Brownie

Page 11

Tenderly

• Intro to Tenderly

Page 12