Multi-Signature Crypto-Wallets: Nakov at Blockchain Berlin 2018 Speaker: Dr. Svetlin Nakov (co-founder of SoftUni) Multisig Wallets. Sign / Execute Transactions. Implementation in Bitcoin and Ethereum Single-User-Managed Wallets: Problems Multi-Signature Wallets: Concepts Multi-Signature Wallets in Bitcoin Multi-Signature Wallets in Ethereum The Gnosis Multisig Wallet: Demo Slides, demos and videos: https://nakov.com/blog/2018/09/26/speaker-at-the-blockchain-technology-conference-2018-berlin/

1. Multi-Signature Wallets
Multisig Wallets. Sign / Execute
Transactions. Implementation in
Bitcoin and Ethereum
Software University (SoftUni)
https://softuni.org
Svetlin Nakov
Blockchain Engineer
and Technical Trainer

2. 2
 Software engineer, trainer, entrepreneur,
PhD, author of 15 books, blockchain expert
 3 successful tech educational initiatives (100,000+ students):
About Svetlin Nakov

3. 3
 Technical advisor @ LockChain / LockTrip: https://locktrip.com
 Raised ~ 10.000 ETH in token sale (Sep-Nov 2017)
 Currently LOC token holders book hotels @ 20-30% better price
 Head of blockchain education (Jan-June 2018) @ Academy
School of Blockchain: https://academytoken.com
 Raised ~ 48M USD in token sale (Jan-Apr 2018)
 Tech advisor for blockchain crypto startups:
 Tokenize Exchange, Bountie, Weidex, IRIS Payments Solutions,
Aeternity Ventures, FFQuest
Nakov – Blockchain & Crypto Projects

4. 4
Book "Practical Cryptography for Developers"
GitHub:
https://github.com
/nakov/practical-
cryptography-for-
developers-book
Official site:
https://cryptobook.
nakov.com

5. Table of Contents
5
1. Single-User-Managed Wallets: Problems
2. Multi-Signature Wallets: Concepts
3. Multi-Signature Wallets in Bitcoin
4. Multi-Signature Wallets in Ethereum
5. The Gnosis Multisig Wallet: Demo

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 Scenario: managing a significant amount of crypto assets:
 E.g. the funds collected during an ICO
 Problems with single-user-managed wallets:
 Lost key / lost password / lost PIN / lost mnemonic phrase
 Stolen / compromised / hacked key
 Illegal activities / intentional fraud
 Accident with the wallet owner
Single-User-Managed Wallets: Problems

7. 7
 A private key can be split into
shares
 E.g. using the Shamir's Secret
Sharing Scheme / Lagrange
interpolation polynomial
 Sample split scheme:
 2-of-3 (any 2 shares out of 3)
 3-of-5 (any 3 shares out of 5)
 Demo: bitaddress.org
Split the Private Key

8. 8
 A multi-signature wallet / multi-signature address
 Holds assets, spendable by N-of-M signatures
 E.g. 2-of-3 means "at least 2 signatures out of 3 owners"
 Creating a multisig wallet
 Specify the owners (public keys / addresses) and threshold
 Submit new transaction for multi-signing
 Sign (confirm) existing transaction (new or partially signed)
 Execute transaction (when enough signatures are collected)
Multi-Signature Wallets: Concepts

9. 9
 A Bitcoin multisig address is created by 3 public keys
 Create tx  sign  signed tx  sign  …  broadcast
Multi-Signature Addresses in Bitcoin

10. 10
 In Ethereum a multi-signature wallet can be implemented as
Solidity smart contract
 Example: the Gnosis multisig wallet contract
 https://github.com/gnosis/MultiSigWallet/blob/master/contracts/
MultiSigWallet.sol
 Used by Gnosis, Aragon, Bancor, Golem and many others
 Golem: 0x7da82c7ab4771ff031b66538d2fb9b0b047f6cf9
 Aragon: 0xcafe1a77e84698c83ca8931f54a755176ef75f2c
Multi-Signature Wallets in Ethereum

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 Create new wallet
 Submit a transaction to the wallet and sign it
 Confirm (co-sign) existing transaction in the wallet
 Execute existing transaction (after the signatures are collected)
The Gnosis Multisig Wallet Contract
function MultiSigWallet(address[] owners, uint threshold)
function submitTransaction(address dest, uint val, bytes data)
function confirmTransaction(uint transactionId)
function executeTransaction(uint transactionId)

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The Gnosis Multisig Wallet: Demo

13. ?
Multi-Signature Crypto Wallets
https://softuni.org

14. License
 This course (slides, examples, demos, videos, homework, etc.)
is licensed under the "Creative Commons Attribution-
NonCommercial-ShareAlike 4.0 International" license
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15. Trainings @ Software University (SoftUni)
 Software University – High-Quality Education,
Profession and Job for Software Developers
 softuni.org
 Software University Foundation
 softuni.foundation
 Software University @ Facebook
 facebook.com/SoftwareUniversity
 Software University Forums
 forum.softuni.bg