Slides I used for Lecture 11 of FinTech - Financial Innovation and the Internet 2021 Fall at Graduate School of Business and Finance, Waseda University on December 10, 2021.
and the Internet 2021 Fall Lecture 11 : Further Smart Contracts Kenji Saito, Graduate School of Business and Finance, Waseda University Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.1/36
required Zoom names : change your names to whatever you want to be called Please link your Zoon names to your real names in your reports Zoom names are important, because if you choose to be called by your real names, still I don’t know whether I should call you by your given or family names You do need to speak often (we are going to have a lot of dialogues) We will use breakout rooms a lot, but those won’t be recorded unless you do it yourselves (need to be allowed) ↑ Well, not so much so far. . . because we are familiarizing ourselves with new concepts first Later on, hopefully we will move to a stage with a lot more dialogues Keep your Zoom client updated! We might use latest features Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.2/36
and chat text will be posted at Moodle and Discord Trial automatic transcription will be posted at Discord Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.3/36
Lecture 2 10/1 Overview of FinTech (2) • Lecture 3 10/8 Internet Technology and Governance (1) • Lecture 4 10/15 Internet Technology and Governance (2) • Lecture 5 10/22 Internet Governance and the World of Apps • Lecture 6 10/29 The World of Apps - continued • Lecture 7 11/12 Basics of Cryptography and Blockchain • Lecture 8 11/19 Blockchain • Lecture 9 11/26 Blockchain and Smart Contracts • Lecture 10 12/3 Smart Contracts • Lecture 11 12/10 Further Smart Contracts • Lecture 12 12/17 DeFi : Decentralized Finance Lecture 13 1/7 Cyber-Physical Society and Future of Finance Lecture 14 1/14 FinTech Ideathon Lecture 15 1/21 Presentations and Conclusions Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.4/36
of Blockchain Brief Introduction to Upgrading and Governance of Blockchain Assignment Review — Science Fiction Prototyping Smart Contracts and Ethereum Just started Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.5/36
With demo Understanding Applications of Blockchain Assignment Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.6/36
GENERATION SMART CONTRACT & DECENTRALIZED APPLICATION PLATFORM” Applying blockchain technology Targeted average block interval : 15 seconds Put a programming language on it Turing complete = can emulate a universal Turing machine (roughly speaking, a computer) (well that’s almost a definition of a programming language) Foundation for DApps (applications that automate the center) An attempt to make the current financial and monetary system obsolete That’s what smart contracts are all about Automate digital asset transfers and their state transitions Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.8/36
DPOUSBDUDPEF NFTTBHFPSBOFXBVUPOPNPVTPCKFDU EBUBFYDIBOHFEBNPOHBDDPVOUTPS&UIFS TUPSBHF TUBUF` TFUPG USBOTBDUJPOT EJHJUBMTJHOBUVSF &7. IVNBO GPSFYBNQMF Blockchain = Run of a state machine (state transition system) = Operation of a computer Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.9/36
External Actor A real person/entity who can digitally sign, having an account EOA : Externally-Owned Account Autonomous Object (internal actor) Operates autonomously within the system, and has an account That said, if you don’t send a message, it won’t work (and miners run them) Account Has an Ether balance, and can have storage (state) and EVM code EVM Code Smart contract program Smart contract = application program on Ethereum = intelligent contract Authenticity is ensured by being written in blockchain Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.10/36
JOWPLF DPOUSBDUDPEF NFTTBHFPSBOFXBVUPOPNPVTPCKFDU EBUBFYDIBOHFEBNPOHBDDPVOUTPS&UIFS TUPSBHF TUBUF` TFUPG USBOTBDUJPOT EJHJUBMTJHOBUVSF &7. IVNBO GPSFYBNQMF BVUPOPNPVT PCKFDU Triggered when an autonomous object receives a message, performs a contract, and changes state Gas must be supplied for each execution step (to avoid an infinite loop and to compensate the miner) (partially burnt) Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.11/36
smart contracts on EVM, https://eth-brownie.readthedocs.io/en/stable/ Today, we will use the Python interpreter environment it provides And infura.io that provides accesses to Ethereum (main and test) networks, https://infura.io Let’s demonstrate sending some fractions of Ether between accounts Both on memory (simulated network) and on a test network Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.12/36
secrecy (guarantee of verifiability to all) Oneness (distribution vs. replication) Not scalable (do not scale if replicated to all participants) Harder governance of evolution (can’t change if everyone needs to be united) Incentive mismatch (discrepancy of motivations for participation in infrastructure and applications) Supported by the value of the native currency (crash would stop all applications) ⇒ Can be solved by redesigning it zero-base Actually in progress (ex. BBc -1) Problem with many ledgers is that they are not redesigned zero-base ex. Hash-chains without proof of work can be tampered with ex. Talking about “newspaper model”, you can’t prove anything by publishing articles in company newsletters Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.13/36
transaction finalization mechanism (Casper) Difficulty of secrecy (guarantee of verifiability to all) ⇒ ZoE (Zcash on Ethereum) Oneness (distribution vs. replication) Not scalable (do not scale if replicated to all participants) ⇒ Sharding, Plasma (multi-layered) Harder governance of evolution (can’t change if everyone needs to be united) ⇒ Benevolent Dictator For Life (BDFL) (with bitter smile ;) ) Incentive mismatch (discrepancy of motivations for participation in infrastructure and applications) Supported by the value of the native currency (crash would stop all applications) ⇒ Will people who want to run the apps buy Ether and support? Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.14/36
probabilistic behavior before transaction commits Difficulty of secrecy (guarantee of verifiability to all) ⇒ Transaction content is kept secret outside the domain, and can be encrypted inside Oneness (distribution vs. replication) Not scalable (do not scale if replicated to all participants) ⇒ Scale-out on a domain-by-domain basis, intra-domain DHT in the future Harder governance of evolution (can’t change if everyone needs to be united) ⇒ Autonomy by domain (don’t care about intra-domain protocols) Incentive mismatch (discrepancy of motivations for participation in infrastructure and applications) Supported by the value of the native currency (crash would stop all applications) ⇒ No native currency, proof of context work by mutual aid Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.15/36
or interpreters) EVM is a stack machine (stack calculator) (see Lecture 6) Programmers don’t usually program in bytecode or machine languages Requires compilers for other, high-level languages High-level language : human-readable/writable language On the other hand, languages close to machines are called low-level languages . . . We may be scolded by artificial intelligence in the near future ;) Examples : Solidity — JavaScript-like language Current primary language Vyper — Python-like language LLL — Lisp-like language Fe — Rust-like features with reference to Vyper? ← NEW! Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.17/36
to, uint256 value) public returns (bool) { balances[msg.sender] = balances[msg.sender] - value; balances[to] = balances[to] + value; return true; } . . . This can be the core of a (not-so-secure) token contract Without considering overflow/underflow A token contract typically manages the balances of all users Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.19/36
as a template (type or class) Constructor is called during deployment Deploy here means to deploy the contract to the blockchain Decides what parameters to pass to the constructor upon deployment Conforms to Ethereum programming model Deployed contract is a specific entity (instance) Has an account (identified by the address, just like a human user) Has storage and ETH balance Can send messages to other contracts Model where deployed contracts are manipulated by sending messages On the assumption that the authenticity of the code that responds to the message is guaranteed Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.20/36
validation process, and reflect the results in the “world state” Redundant verifiers Closed within the state of blockchain (maintained by the verifiers) This design is consistent in the Ethereum system Challenges I/O commands cannot be issued from within the program Not affected by the outside world other than external actors who send signed messages ⇒ ex. Data from sensors cannot be read directly (problem of an oracle) Not able to directly affect the outside world ⇒ ex. Cannot send commands to the motor to turn it on/off Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.21/36
real-estate brokerage, banking, and Legal Affairs Bureau (or judicial scrivener) Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.22/36
SFUVSOMBOE 1VSDIBTF$POUSBDU -BOE"TTFU MBOE EFQPTJU USBOTGFSMBOESJHIUTUPCVZFS USBOTGFSQBZNFOUUPTFMMFS QBZNFOU EFQPTJU %JHJUBM5PLFO DSFBUFBOEpYJOUIFBJS FJUIFSDBOEPUIJT DSFBUFBOEpYJOUIFBJS DBOGSFFMZKPJOBOEMFBWF DBOGSFFMZKPJOBOEMFBWF 4FMMFS #VZFS JOUFSOBM TUBUF SFUVSONPOFZ TFUUMF USBOTGFS JOUFSOBM TUBUF USBOTGFS JOUFSOBM TUBUF 1. Purchase contract is fixed in the air to prevent taking away of land or money (both parties can verify the contract) 2. Deposit land rights and purchase money in the contract (if they change their minds, they can take them back) 3. When settled (anyone can do it if both right and money are deposited), the rights and money for the property are transferred simultaneously Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.23/36
clone https://github.com/ks91/sample-smart-contracts.git Follow README 1. Setup a sample token project with brownie Brownie is a Python-based Ethereum programming and test environment Javascript-based one is called Truffle, and an Ethereum remote procedure call client is called Ganache See? Engineers are fun people to work with! 2. Copy the content of contracts, scripts and tests directories of this sample project into the corresponding directories of the token project 3. Compile 4. Test Today, I will demonstrate manually the test for automated escrow Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.24/36
>= _price_); /* ’this’ means this contract */ require(_asset_.getOwner() == address(this)); _token_.transfer(_seller_ , _price_); _asset_.transfer(_buyer_); emit Settled(); /* event log */ return true; } Just to introduce the settle() part from the sample code Only if both the price and the asset are deposited with the contract, It transfers money to the seller and asset to the buyer Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.25/36
>>> network.disconnect() # disconnect from the default, simulated environment of Ethereum >>> network.connect(’ropsten’) >>> len(accounts) 0 >>> accounts.add(paste the hexadecimal string of the private key here) <LocalAccount object ’hexadecimal string of the account’> >>> accounts[0].balace() Here is the ETH balance of the account We set up two accounts Once you have created multiple accounts, you can try to transfer ETH, for example as follows >>> accounts[0].transfer(accounts[1], "1 ether") But before that, you may want to feed the accounts with Ropsten ETH from some public faucet Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.26/36
test_deploy_and_settle(Token, IndivisibleAsset, OneTimeEscrow): asset = accounts[0].deploy(IndivisibleAsset, "5322 Endo", "mˆ2", 300) token = accounts[0].deploy(Token, "Test Token", "TEST", 18, "1000 ether") Deploying token and asset contracts The above is just the test code as it is, so in the console we will just type the inside of the function First, let’s do seller = accounts[0] and buyer = accounts[1] for readability Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.27/36
token, accounts[1], asset, accounts[0], 300) Sending 300 coins from seller (accounts[0]) to buyer (accounts[1]) to prepare Because the buyer has to cast a transaction that pays 300 coins Deploying Escrow Contracts Buyer is accounts[1], seller is accounts[0], and the price is 300 coins Since we are using the sample arguments of the baked Token as they are, 300 coins is actually a very small unit, like wei in ETH Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.28/36
assert token.balanceOf(accounts[0]) == 999999999999999999700 assert token.balanceOf(accounts[1]) == 0 assert token.balanceOf(escrow) == 300 assert asset.getOwner() == escrow Buyer (accounts[1]) deposits 300 coins in escrow, and Seller (accounts[0]) deposits the asset in escrow assert tests a statement, and fails the test if it turns out to be false But we are in console (not doing an automated test), so we just see the values Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.29/36
token.balanceOf(accounts[1]) == 0 assert token.balanceOf(escrow) == 0 assert asset.getOwner() == accounts[1] Calling settle() and closing the transaction In this code, it is called by seller (accounts[0]), but it is OK to call from either side Let’s see some transactions on an Ethereum Ropsten testnet explorer Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.30/36
contract execution as a verifier ⇒ Everyone has access to the contract code It is in principle verifiable that the correct contract is being executed I/O is outside blockchain → this is possible without revealing the entirety of the agreement True worth of smart contract is that everyone can confirm that “the correct contract was executed”? Program code and its execution results as “record whose contents and existence cannot be denied by anyone” But Ethereum’s method should not be the only one There are many issues including how to manage the contracts’ life cycles We have already talked about The DAO Incident Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.31/36
Fungible Redeemable Non-fungible Redeemable Non-fungible Non-redeemable Certifying Identifying payment ID card security token last will logistics insurance claim Tracking Sensing fiat money crypto-pet Proves you are the one since you can handle the private key? Transfers numerical representations of debt / asset? Maintains authenticity of registered code, data and resulted states? (Authority) issues certificates about some content? Updates records about sustained presences? Is data still valid even if the subject is gone? Many think we implement token and provenance apps with smart contracts, but. . . Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.33/36
investment fund “The DAO” leaked 3.5M ETH in an attack that exploited a bug in a smart contract, but this incident was made to look like it never happened, by the hard fork of Ethereum (1) Choose between A) public policy position (of a country with many victims), or B) management position at The DAO (2) Discuss briefly what would have been the best thing to do from your position Deadline and how to submit December 14, 2021 at 17:59 JST From Moodle (mandatory) — this time, we are using a Q&A forum So that your classmates can read your report, refer to it, and comment on it Optionally, you can also post to #assignments channel at Discord So that anyone in our Discord can read your report, refer to it, and comment on it Just plain text, and be concise, please Lecture 11 : Further Smart Contracts — FinTech — Financial Innovation and the Internet 2021 Fall — 2021-12-10 – p.35/36
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![Test Code (2) token.transfer(accounts[1], 300, {’from’: accounts[0]}) escrow = accounts[0].deploy(OneTimeEscrow,](https://files.speakerdeck.com/presentations/3bea8f7e127c47c8b52a6c1a6d8eb32d/slide_27.jpg){kind=link}
![Test Code (3) token.transfer(escrow, 300, {’from’: accounts[1]}) asset.transfer(escrow, {’from’: accounts[0]})](https://files.speakerdeck.com/presentations/3bea8f7e127c47c8b52a6c1a6d8eb32d/slide_28.jpg){kind=link}
![Test Code (4) escrow.settle({’from’: accounts[0]}) assert token.balanceOf(accounts[0]) == 1000000000000000000000 assert](https://files.speakerdeck.com/presentations/3bea8f7e127c47c8b52a6c1a6d8eb32d/slide_29.jpg){kind=link}
