Smart Contracts - Ethereum


Blockchains allow us to record information. Wallets allow us to control the information. What if we want to add additional functionality to the information, like the ability to configure a set of advanced rules to provide more flexibility to its access, or the ability to interact with other chains or the outside world?

Bitcoin added support for a basic scripting language that allows for uses cases such as multi-party signers, atomic swaps, time-locked transactions and tokenization. This scripting language is purposely limited in order to minimize the potential for attacks against the network.

There are some who believed the language capabilities should be expanded. In 2014, Vitalik Buterin approached the Bitcoin maintainers about this. They declined his request, so he created his own blockchain and called it Ethereum.

The fundamental difference between Ethereum and Bitcoin is in the capability of their scripting languages. The main purpose of Bitcoin is for peer-to-peer payments, whereas Ethereum aims to be a distributed world computer.

With Ethereum’s turing-complete programming language, anyone can write smart-contracts and decentralized applications (dApps), where they can create their own arbitrary rules for ownership, transaction formats and state transition functions.

One problem with having a powerful scripting language is that it only has access to a finite amount of computation resources in the network. It is easy to accidentally (or maliciously) over-consume these resource, effectively jamming the system for everyone else.

The solution to this problem is to charge a fee proportional to the resources being used. Ethereum uses Ether (ETH) as its the currency token. Every time you make a transaction, you pay a small fee (the “gas fee”) in ETH. By requiring a fee for every computation executed on the network, bad actors are discouraged from spamming the network. The fee does have the consequence that in times of high demand, costs to transact can become prohibitively expensive. Dealing with this problem will be addressed in the Scaling section later.

Smart Contracts & Security

Smart contract is the term used for a program that is written and deployed onto a blockchain. Once deployed, the contract cannot be altered (immutability), except by narrow parameters allowed in the programming. This immutability, especially when augmented with the open-source publication of its implementation, allows the contract to develop a reputation of consistency and trust that will encourage other users to interact with it.

Smart contracts that perform useful actions can charge fees of its users and become a profit-center for its creators.

Smart contracts can do an increasingly number of things:

  • Customizable tokens
  • Decentralized finance (DeFi)
  • Decentralized autonomous organizations (DAOs)
  • User account-abstraction
  • Cross-chain bridges
  • Interaction with oracles
  • and many more…

Security Considerations

The biggest tradeoff to consider with smart contracts is security. As with all human-programmed applications, mistakes are inevitable. Bugs in smart contracts can be exploited and the consequences are more significant than in regular applications because tokens with monetary value are often at stake. Hacks on smart contracts have drained billions of USD$ in value from networks over the past several years. Time and attention are the only remedies for security flaws. As the industry matures, vetted building blocks will emerge that can be used to build smart contracts with more security guarantees. These are beginning to exist in some areas. Some best practices to be aware of can be found in the following videos.


We’ve discussed Bitcoin and Ether as built-in units of currency in their respective networks. Another general word for them is “tokens”. A token is simply an exchangeable unit of value. It may carry with it some information. Here is an article from Coinbase that discusses the topic further.

These built-in tokens are not the only tokens allowed in blockchain networks. Smart contracts gives users the ability to create their own tokens and attach their own rules for use in their own custom services.

To define a new token within an existing network is generally much easier than building a whole new network with a new base token. Once the developer chooses a network with the desired security and performance properties, then they can use network-provided standards and tooling to streamline the creation of tokens.

Why create a new token?

Tokens represent niche communities; they represent brands. They encode a custom set of rules, a unique ethos or spirit, that applies to the applications and groups that they belong to. Any token built on a network increases the general usage on that network and demand for that networks fundamental currency.

Types of tokens

There are two classes of tokens: fungible and non-fungible.

Fungible tokens

Up to this point we have only discussed fungible tokens. Fungible means that any one token is the same as the other. Cash is fungible. It does not matter which USD$1 bill you present at a store, they all have the same value as each other.

In order to make custom-designed tokens exchangeable, several fungible token standards have been created. The most well know is the Ethereum ERC-20 standard. Other networks tend also use the Ethereum standards, since those were the first, in order to retain compatibility and leverage pre-existing expertise and tooling.

Non-fungible tokens (NFTs)

Non-fungible tokens (NFTs) are issued as families. Each token carries unique information and capabilities, and each is valued independently. The family grouping only serves to communicate a common creator or a common usage domain.

There are several standards for NFTs. The most common Ethereum standard is ERC-721.

NFTs are most popularly used to represent ownership of a given piece of digital artwork. The first NFT: minted in 2014, when bitcoin had a value of about $630, Kevin McCoy created an animation, made entirely out of code, it was originally published to Namecoin blockchain, but has since been transferred to the ethereum blockchain. Fun Fact: the token url points to a json stored on IPFS check out how that works in this short video.

NFT History
In 2017 CryptoKitties were the first NFTs minted using ERC-721.

NFTs can represent both digital assets (GIFs, collectibles, music, videos, etc.) and non-digital assets (legal documents, signature, invoice, deeds, etc.) including all of the following:

  • Digital Content: NFTs enable content creators to own their work. When creators sell their content, funds go directly to them. If the new owner then sells the NFT, the original creator can even automatically receive royalties, baked into and ensured by the metadata.

  • Gaming: NFTs can provide records of ownership for in-game items, fueling in-game economies. In regular games you can buy items for in-game use. With NFTs, you can recoup your money by selling game items as stand-alone products.

  • Domain-names: ENS domains are also NFTs, allowing a unique and easy way to remember IP addresses.

  • Physical Items: NFTs could eventually act as deeds to physical items such as your house or car. one day you could buy a car or home using ETH and receive the deed as an NFT in return (in the same transaction).

  • Fractional Ownership: NFT creators can also create “shares” for their NFT, allowing people to own a part of an NFT without having to buy the whole thing. It’s very likely that one day soon owning a fraction of an NFT will enter you into a decentralized autonomous organization (DAO) for managing that asset.

Notable NFT collections:

Crypto Kitties –

Crypto Kitties

Crypto Punks –

Crypto Punks

Bored Apes –


Loot –


NBA Top Shots –

NBA Top Shots

Beeple –


Market Places

NFTs are typically traded in specialized marketplaces, like:





Dapps, DAOs, and DeFi

Smart contracts have sparked an explosion of services in every network. Decentralized applications (dApps) are apps that communicate with a smart contracts. Decentralized autonomous organizations (DAOs) take the application one step further and use smart contracts to define membership and governance rules. DAOs allow humans to adapt, govern, regulate, and act both on chain and in the real world, in accordance with rules that are clearly defined and perfectly enforceable through smart contracts. Decentralized finance (DeFi) is is a growing ecosystem of financial services controlled by smart contracts.


Key features of dapps:

  • Open-source
  • Public data and records
  • Uses a cryptographic token to help keep the network secure

Common categories of dApps:

  • Finance
  • Art and collectibles
  • Gaming
  • Technology

dApp visualization


The ethos behind DAOs is to enable collective decision-making, guard-railing against unbalanced organization structures. A popular analogy is that DAOs are modern-day, tech-enabled co-ops.

DAO members are not only participants in, but also owners of the DAO. Members are given tokens which grant them equity ownership in the DAO, as well as voting power in on-chain governance decisions.

Here are some components of DAO structure:

  1. Mission. DAOs need a mission/purpose. This can be collecting NFTs, building a product, funding public goods, etc.
  2. Group chat. DAOs usually start off with a small group of people in Telegram group or Discord server that share the same interest(s) or goal(s).
  3. Treasury. The most common type of Community DAO collects NFTs and stores them in a multi-sig. Community DAOs can also bootstrap their treasury through a tokenized crowdfund.
  4. Governance. Community DAOs with valuable treasuries and 100+ members need a way to make collective decisions. Usually, rough consensus is reached off-chain and the governance vote is just a formality. Also, most Community DAOs empower small, focused teams of 5-10 members to own specific work-streams instead of requiring a governance proposal for every decision.
  5. On-chain cash flow. This is the most nascent component of Community DAOs but also the most interesting. On-chain cash flow turns a group chat into a sustainable business. So far, the most common way to generate on-chain cash flow has been through NFT drops.
  6. Token. Community DAOs often issue an ERC-20 token as a way to gate membership. It can also serve as a funding mechanism.

Types of DAOs:

  • Protocol DAO: Networks issue a token, allowing community members to govern the protocol
  • Grant DAO: Communities donate funds and use a DAO to vote on how capital is allocated to various contributors
  • Social DAO: exactly what it sounds like, good vibes only
  • Investment DAO: Investment DAOs allow members to pool capital and invest in projects at their earliest stages

Decentralized Finance (DeFi)

Smart contracts that facilitate financial transaction marketplaces are classified as decentralized financed or (DeFi). DeFi projects can be DAOs, if there is governance token involved, or they can just be stand-alone smart contracts that perform a given function completely autonomously.

You can think of DeFi in layers:

  1. The blockchain – Ethereum contains the transaction history and state of accounts
  2. The assets – ETH and the other tokens
  3. The protocols – smart contracts that provide the functionality
  4. The applications – the user interface of the system

DeFi visualization

Use Cases

Payments: DeFi makes sending/streaming money around the globe as fast as sending an email.

Lending and Borrowing: You can earn interest on your crypto through lending. Decentralized lending works without either party having to identify themselves. Borrowing money from decentralized providers comes in two main varieties (peer-to-peer, pool-based).

Token Swaps: Decentralized exchanges (DEXs) let you trade different tokens 24/7.

Stable Currencies: Stablecoins are cryptocurrencies without the volatility. How stablecoins get their stability

Advanced Use Cases

Advanced Trading and Prediction Markets:

Investments/Asset Management:

Crowdfunding: Quadratic funding is the mathematically optimal way to fund public goods in a democratic community. Gitcoin is one example. How it works:

  1. There is a matching pool of funds
  2. A round of public funding starts
  3. People can signal their demand for a project by donating some money
  4. Once the round is over, the matching pool is distributed to projects; Those with the most unique demand get the highest amount from the matching pool

Other terms to know

Liquidity Pools are one of the foundational technologies behind the current DeFi ecosystem. A liquidity pool is a collection of funds locked in a smart contract. Liquidity pools are used to facilitate decentralized trading, lending, etc. Liquidity pools are also the backbone of many decentralized exchanges (DEX). Users called liquidity providers (LP) add an equal value of two tokens in a pool to create a market. In exchange for providing their funds, they earn trading fees from the trades that happen in their pool, proportional to their share of the total liquidity.

Yield Farming is a specific use case of liquidity pools. Yield farming, also referred to as liquidity mining, is a way to generate rewards with cryptocurrency holdings by investing and/or lending it.

Total Value Locked (TVL): TVL represents the number of assets that are currently being staked in a specific protocol, the total amount of underlying supply that is being secured by a specific application by DeFi completely. Total value locked is a metric that is used to measure the overall health of the DeFi and yielding market.

Rug Pull: A rug pull is where crypto developers abandon a project and run away with investors’ funds, leaving them “rugged.”

Miner Extractable Value (MEV): the measure of the profit a miner can make through their ability to arbitrarily include, exclude or re-order transactions within the blocks they produce; miners can exploit and profit from front-running, back-running and sandwiching transactions in any block they mine. (More on MEV)