What You Can Do By The End

• Test whether a use case needs a chain
• Describe four real-world uses
• Explain quadratic funding
• Explain how regulators classify activity
• Outline MiCA and the Turkish approach

Recap Of Week 10

• Keys control assets.
• Phishing targets people, not cryptography.
• Reentrancy and access bugs hurt contracts.
• Audits help but promise little.

Does This Need A Blockchain?

• Many parties write to the data.
• They lack a trusted middle party.
• The record must stay verifiable for long.
• Mostly no: use a normal database.

many writers?        -> no  -> database
no trusted middle?   -> no  -> database
long-lived, public?  -> no  -> database
all yes              -> consider a chain

Garbage In, Garbage Kept

• A chain keeps what was written faithfully.
• It cannot tell if the input was true.
• This is the oracle problem again.
• Plan how real-world facts get attested.

Digital Identity Today

• Companies control most online accounts.
• Closing an account erases that identity.
• Self-sovereign identity puts credentials in your wallet.
• You present them when needed.

DIDs And Verifiable Credentials

• A DID is an identifier you control with a key.
• An issuer signs a credential.
• A verifier checks the signature, not the issuer's server.
• Personal data stays off chain.

issuer signs:  {"degree": "BSc", "holder": did}
holder keeps it in a wallet
verifier checks:  signature + issuer key

Supply Chains

• Many companies, many separate records.
• A shared ledger records signed events.
• Pilots exist for food and origin tracking.
• The hardest part is agreeing on formats.

Payments And Stablecoins

• Cross-border bank transfers can take days.
• Stablecoins settle in seconds to minutes.
• Rollups make small payments practical.
• Cash-out still needs exchanges and checks.

Funding Public Goods

• Public goods benefit many and are hard to charge for.
• Markets tend to underfund them.
• Programmable transfers allow new funding rules.
• Open-source software is a typical example.

Quadratic Funding

• Many people donate small amounts.
• A matching pool adds more money.
• Match grows with the number of donors.
• Sybil attacks need identity defenses.

A: 100 donors x 1 = 100 given -> larger match
B:   1 donor  x 100 = 100 given -> smaller match
same total, different breadth of support

How Regulators Think

• They look at the activity, not the technology.
• Fundraising: securities rules may apply.
• Payments: payment and e-money rules.
• Holding assets or running exchanges: licensing.

AML, Travel Rule, Tax

• FATF sets international AML standards.
• Providers identify customers.
• Travel rule: share sender and receiver details.
• Most countries tax gains from trading.

The EU: MiCA

• Adopted in 2023, applied in stages in 2024.
• One rulebook for all member states.
• Issuer white papers and stablecoin rules.
• Service providers must be authorized.

Turkey

• 2021: central bank bans crypto as payment.
• 2024: law places service providers under SPK licensing.
• AML duties are supervised with MASAK.
• Secondary rules continue to develop.

Recap

• Test the need for a chain first.
• Identity, supply, payments, public goods: real but limited.
• Regulators reach the intermediaries.
• Rules change: read official sources.

Next Week: The Capstone

• Design and deploy a small dApp on a testnet.
• Brief, rubric, demo script and peer review.
• Bring a one-sentence idea that passes today's test.

Questions And Exercise

• Pick a use case and apply the test.
• Map intermediaries and one rule from MiCA or SPK.
• Write the half-page memo.