## Ethereum in 30 minutes
---
### Ethereum is a general-purpose blockchain.
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### We used to describe it like this...
<img src="https://lh5.googleusercontent.com/xkkWdbZwXl5VHN8wQRQXdj2OafQ941Fi1TnLc9F82zLpq-jW9hjVa201BWiITK3XU_zFAsukYisP15v1CLBBkh1OsPmTneGJQ8kMKp7cOgbGPXGHwyTt5XUbsj1H-pmWtVb50S2ZPLf3X4k_8g567cMOP5CLGGRGtuBYjdSfD6ee6fjGVqh6Dqy5JDg" style="width: 30%" />
<img src="https://lh4.googleusercontent.com/NxTPwzEPse5gu-ib69I3qCpjoPGJiEz6zUOfOfVua7Ivaz1QLN78LI3yEBuUFgwcqTMZwtcI1-oWUjos4yovKL0VXHIEk17neH_iJgsJA9U37FHQaY-7mI3WjQXSJ3zGcMj9Zb0bg1zrDtXM0t2q0SjE9FiPb7b8fHDEstXx-5ltC-_e19bDhkQo8So" style="width: 30%" />
<img src="https://lh5.googleusercontent.com/QxBjuCDX-ETQEEZDE6xpq3Qp27zrYkE40Kjh3CgMdKnCLiqfaeBZSuJRAgUl-GCWk7CFcVJ89fpnPCnpnGn7AYY0KeXrOsTIADn3t23ju1WIYXAHaXpuXri7Fyd4wcIcuB6wjlNK-G79tW4MWacmTfhx_S9UN-ux35_vCQ3VInF532s2k93VsS-fHxY" style="width: 15%" />
But these days almost every new blockchain is general-purpose...
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### So what does the blockchain look like?
* Blocks contain transactions
* Attestations "confirm" blocks
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### Accounts
<p style="margin: 1px; font-size: 50%"> </p>
<div style="font-size: 83%">
* The information ("**state**") that the blockchain keeps track of is made up of **accounts**.
* There are two types of accounts:
* **Externally owned account (EOA)** - this account represents the user, eg. if you hold ETH, that ETH is stored inside your EOA
* **Contract** - this account is a computer program that lives on-chain. It has a piece of code, and internal storage.
</div>
---
### What do contracts look like?
<div style="font-size: 70%; padding-left: 100px; padding-right: 100px">
```
struct Domain:
owner: address
ip: uint32
domains: public(HashMap[bytes32, Domain])
@external
def set_owner(domain_name: bytes32, new_owner: address):
owner: address = self.domains[domain_name].owner
if owner == convert(0, address) or owner == self:
self.domains[domain_name].owner = new_owner
@external
def set_ip(domain_name: bytes32, ip: uint32):
if self.domains[domain_name].owner == self:
self.domains[domain_name].ip = ip
```
</div>
---
### Transaction flow example
<img src="https://i.imgur.com/M1AqQjs.png" style="width: 60%" />
---
## Gas
<p style="margin: 1px; font-size: 50%"> </p>
<div style="font-size: 83%">
* Gas is the "unit" of resource consumption within Ethereum
* Gas cost examples:
* A transaction costs a "base" 21,000 gas
* Each computational step costs ~2-10 gas (usually)
* Editing a storage slot costs 5,000 gas (20,000 if slot not filled yet)
* Each byte of data costs 16 gas (4 if zero byte)
</div>
---
### Gas
<p style="margin: 1px; font-size: 50%"> </p>
<div style="font-size: 83%">
* If you send a transaction which gets included in a block, you must pay a fee proportional to how much gas the transaction consumed
* <code style="color: yellow">fee = (base_fee + priority_fee) * gas_used</code>
* Base fee: burned, value determined by protocol
* Priority fee: paid to block proposer
* A maximum of 30,000,000 gas can be spent in each block
</div>
---
### Full transaction object
<p style="margin: 1px; font-size: 20%"> </p>
<small>
| Name | Type | Description |
| - | - | - |
| Tx type | byte | Here: 0x02 |
| Chain ID | int | Which chain is this tx for? |
| Nonce | int | Anti-replay value |
| Max priority fee | int | Priority fee per gas, for block proposer |
| Max fee | int | Max total fee (base + priority) per gas |
| Gas limit | int | Max gas this tx is allowed to consume |
| Destination | address | Which address this tx goes to |
| Amount | int | How much ETH to send |
| Data | bytes | Data passed in call if destination is a contract |
| Access list | List[Tuple[int, List[int]]] | Accounts and storage slots to more cheaply pre-access |
| Signature (3 fields) | (bool, int, int) | Verifies who sent it |
</small>
---
### High level languages
---
### Proof of stake consensus
<p style="margin: 1px; font-size:50%"> </p>
* Deposit 32 ETH, become a validator
* Each slot, 1/32 of all validators attest to the block created during that slot
* Validator revenue:
* In-protocol rewards
* Priority fees and MEV from transactions
* Validators can withdraw at any time, with a delay
---
### Fork choice
<p style="margin: 1px; font-size:50%"> </p>
---
### Casper FFG finalization
If > 2/3 of validators online + honest, then after 2 epochs a block is finalized, and *cannot* be reverted.
<small>(Though in practice 1 "safe" slot is enough for many apps)</small>
---
### Merkle trees
---
### Merkle trees in Ethereum
<p style="margin: 1px; font-size:50%"> </p>
<img src="https://lh5.googleusercontent.com/LQRvMnRw3vPLbpl15QICOFNcc_ttJJO48Lur9rbAMKKPlU5NOrAC2fKsrkblMYY68pskBr_LuETeCBw-ugDX9qybenySBVcvRKGPfPgDf8YLyQtr4O_rTs9sIX66G7sBdoD-Rcj1bxYHNcbT-JRdKS0JYo-vLmi0uYUuUdp1NjMQ86QoBr8if_bTcZ0" style="width:31%"/>
<img src="https://lh6.googleusercontent.com/LuRmHqCT-roFyj1l9yOOM2CzFxFrkkw8C448jyR0PV3-0o14KLw0Z60SY2jLC4A3E24bQN7GhQeVUC6MVJKWN3yviDCWPsP5aFcVcGPL2r96zeuUmScW09Huem575M9ABdVdNGEZbbvTZhxwJekCa2TbpRIWWlEPRWsDN5FZA2YMafFAHAOAPTJCoe4" style="width:34%"/>
<br>
<p style="margin: 1px; font-size:50%"> </p>
* Allow for efficiently verifiable proofs that something happened in a block
---
### Merkle trees in Ethereum
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### Layer 2 protocols
<p style="font-size: 83%">It is increasingly popular for users to "live" not on Ethereum directly, but on "layer 2" protocols that inherit security from Ethereum, and add higher scalability on top.</p>
---
### Layer 2 protocols
<img src="https://i.imgur.com/RnPpA7k.png" style="width: 38%" />
<p style="margin: 1px; font-size:50%"> </p>
<div style="font-size: 83%">
* From a user's point of view, living on a modern layer 2 feels like living on Ethereum. Applications work the same way.
* However, fees are many times lower.
</div>
---
### Future directions
<p style="margin: 1px; font-size:50%"> </p>
<div style="font-size: 83%">
* **The Merge**: Done! But PoS can be improved with single slot finality
* **The Surge**: Improved scalability through rollups, danksharding and ZK-SNARKs
* **The Verge**: Replacing Merkle trees with more efficient data structures that let Ethereum nodes be much lighter ("stateless clients")
* **The Purge**: Clearing out old data and technical debt
* **The Splurge**: a grab bag of various useful stuff: account abstraction, EVM improvements, PBS...
</div>
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