The Problem with Traditional Finance#

The current financial system, with its paper-based origins and siloed databases, is fundamentally incompatible with the speed and global nature of the modern internet. Cross-border payments take days, settlement involves layers of intermediaries, and fees are opaque. The core issue? “Not your keys, not your money.”

The Vision: A Unified Global Ledger#

The Internet Capital Market is the idea of a single, permissionless, global ledger for all financial assets. It’s more efficient, more transparent, and more accessible. And it’s powered by blockchain technology.

A compelling angle discussed was the convergence of AI and Crypto. As AI agents become more sophisticated and begin managing assets on our behalf, they will need a protocol they can “understand” to transact. Blockchain provides exactly that: a machine-readable, trustless protocol for value transfer. Imagine AI agents settling invoices or managing supply chain payments directly on Solana via protocols like X 402.

Why Solana? The L1 Advantage#

A key argument for Solana over Layer 2 solutions is unified liquidity.

Solana has also proven itself under pressure. Even during extreme events like high-profile token launches, the network has remained stable. This battle-tested reliability, combined with its focus on real protocol revenue (not just fundraising narratives), makes it a compelling infrastructure choice.

The Three Pillars of an Internet Capital Market#

1. Payments: Stablecoins like PYUSD (PayPal) enable instant, low-cost global transactions. Major players like Visa and Stripe are already integrating Solana for settlement.
2. Trading & RWA: Real-world assets are being tokenized on Solana. Platforms like Xstock allow users to trade tokenized US equities (NVDA, TSLA) 24/7. These tokens can then be used as collateral in DeFi protocols, earning “dividend + DeFi yield.” Over $1 billion in RWA is now on Solana, with institutions like BlackRock and Franklin Templeton participating.
3. Fundraising: The line between traditional IPOs and token launches is blurring. Projects can raise capital directly from a global pool of investors without needing investment banks.

Fixing a Critical Security Bug#

First, a callback to our previous lesson. Our “Simple Chain Storage” program had a severe vulnerability: it calculated the PDA but never verified that the account passed by the user actually matched that PDA.

The Vulnerability: An attacker could pass in any account as the pda_account, potentially overwriting other users’ data.

The Fix: Always assert that the derived PDA matches the account provided.

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// 1. Calculate the expected PDA
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let (expected_pda, _bump_seed) = Pubkey::find_program_address(
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    &[b"my_seed", user_account.key.as_ref()],
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    program_id
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);
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// 2. Verify the account passed in matches the expected PDA
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assert_eq!(
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    pda_account.key,
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    &expected_pda,
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    "PDA account mismatch!"
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);

Design Philosophy: In Solana, you don’t need to explicitly store an owner field. If you verify that a PDA is derived from a user’s public key, and that user has signed the transaction, you have cryptographically proven ownership.

Blockchain as a State Machine#

Before coding, let’s understand the theory.

• UTXO Model (Bitcoin): The chain validates state transitions. “Can I go from State A (crouching) to State B (2 meters in the air)?” It doesn’t compute the path.
• Account Model (Solana/Ethereum): The chain executes an action on a state. “I am crouching. I perform a ‘jump’ action. The VM computes my new state: 2 meters in the air.”

Designing the Thai Zhu Coin#

Goal: A minimal, custom token where we implement mint and transfer instructions ourselves.

Account Data: Each user has a PDA storing a single u64 balance (8 bytes, Big Endian).

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pub struct ThaiZhuAccount {
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    pub balance: u64,
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}

Instruction Data (9 bytes total):

Defining Account Inputs#

Solana requires you to explicitly list all accounts an instruction will interact with.

Mint Instruction (Create new tokens)

Transfer Instruction

Key Implementation Details#

1. Auto-Initialization (Better UX)

When transferring tokens, if the recipient doesn’t have a token account yet, our program will automatically create one. The sender pays the rent. This removes a friction point where users would otherwise need to “register” before they could receive funds.

2. Safe Math (Prevent Exploits)

Arithmetic in crypto is dangerous. An integer underflow (e.g., 50 - 51) on an unsigned integer can wrap around to a massive number, effectively printing money for an attacker. Rust’s checked_sub and checked_add return None on overflow/underflow, letting us handle it gracefully.

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// ❌ DANGEROUS: Wraparound vulnerability
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// from.balance -= amount;
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// ✅ SAFE: Returns an error if underflow would occur
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from.balance = from.balance
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    .checked_sub(amount)
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    .ok_or(ProgramError::InsufficientFunds)?;
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to.balance = to.balance
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    .checked_add(amount)
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    .ok_or(ProgramError::Overflow)?;

Atomicity: Solana instructions are atomic. If checked_add fails after checked_sub has already happened, the entire transaction reverts. The state is never corrupted.