The Evolution of Finance on the Blockchain#

The crypto industry has gone through distinct phases:

1. 2009 - Bitcoin: Introduced peer-to-peer payments and the idea of disintermediation.
2. 2020 - DeFi Summer: The explosion of decentralized applications like Uniswap established Ethereum as the “world computer.”
3. Now - The Internet Capital Market: The focus is shifting from pure decentralization to compliance and enterprise adoption. The goal is to bring the entire global capital market onto a unified, transparent, and efficient blockchain network.

This new paradigm rests on three pillars: Stablecoins, Real World Assets (RWA), and Payments.

Stablecoins: The Foundation#

Stablecoins are the bridge between traditional finance and the on-chain world. There are two primary models:

Solana’s Token-2022 (Token Extensions) standard provides native features crucial for compliant stablecoin issuance:

• Permanent Delegate: Allows the issuer to retain control (freeze/burn tokens), a legal requirement in many jurisdictions.
• Transfer Hook: Executes a custom program on every transfer, enabling real-time KYC/AML checks.
• Confidential Transfer: Hides transfer amounts using cryptography, expected to see widespread adoption starting in 2026.

Real World Assets (RWA): Tokenizing Everything#

RWA represents the next frontier: bringing off-chain assets onto the blockchain.

• From T+2 to T+0: Traditional settlement takes days. With tokenized assets, settlement is instant and global.
• The Asset Ladder:
  • Level 1 (Stablecoins): The earliest form of RWA.
  • Level 2 (Treasuries/Money Market Funds): Major players like BlackRock and Franklin Templeton are issuing tokenized fund shares on Solana.
  • Level 3 (Equities): Companies like Xstock are tokenizing US stocks, enabling 24/7 trading, fractional ownership, and DeFi composability (e.g., using stock tokens as collateral for loans).

The Solana Account Model Revisited#

Remember, in Solana, everything is an account. Here’s a quick refresher on the structure:

SBF and the Program Entrypoint#

Solana programs are compiled to SBF (Solana Bytecode Format), a sandboxed, high-performance virtual machine format derived from BPF.

A Solana program doesn’t have a main function. Instead, it uses the entrypoint! macro to define its entry point:

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entrypoint!(process_instruction);
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fn process_instruction(
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    program_id: &Pubkey,      // This program's ID
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    accounts: &[AccountInfo], // All accounts passed to the instruction
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    instruction_data: &[u8],  // The instruction's parameters (raw bytes)
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) -> ProgramResult {
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    // Your business logic here...
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    Ok(())
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}

Key Concepts for the Storage Program#

1. Program Derived Addresses (PDAs)

A PDA is an account whose address is deterministically derived from a program ID and a set of “seeds.” Think of it like this: your company (the Program) opens a subsidiary bank account (the PDA). The account is technically owned by the company, but you, as an employee, can manage it through official company procedures.

• Key Property: A PDA has no private key. It cannot sign transactions. The program must use invoke_signed to authorize actions on its behalf.

2. Rent Exemption

To prevent state bloat, Solana requires accounts to hold a minimum SOL balance (rent). If an account holds enough SOL to cover two years of rent, it becomes rent-exempt and the balance is never debited.

• Calculation: Rent::get()?.minimum_balance(data_length)

The Code: Initialize and Write Data#

Let’s write the logic to create a user’s storage account and write initial data to it.

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// 1. Get accounts from the instruction
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let account_info_iter = &mut accounts.iter();
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let user = next_account_info(account_info_iter)?; // The user (signer, pays fees)
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let pda_account = next_account_info(account_info_iter)?; // The storage PDA
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let system_program = next_account_info(account_info_iter)?;
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// 2. Derive the PDA and verify it matches the one passed in
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let (expected_pda, bump_seed) = Pubkey::find_program_address(
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    &[b"storage", user.key.as_ref()],
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    program_id
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);
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assert_eq!(pda_account.key, &expected_pda);
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// 3. If the PDA doesn't exist yet (has 0 lamports), create it
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if pda_account.lamports() == 0 {
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    let space = instruction_data.len();
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    let rent = Rent::get()?.minimum_balance(space);
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    // CPI (Cross-Program Invocation) to the System Program
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    invoke_signed(
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        &system_instruction::create_account(
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            user.key,
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            pda_account.key,
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            rent,
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            space as u64,
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            program_id // Set the new account's owner to this program
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        ),
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        &[user.clone(), pda_account.clone(), system_program.clone()],
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        // The seeds used to sign for the PDA
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        &[&[b"storage", user.key.as_ref(), &[bump_seed]]],
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    )?;
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}
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// 4. Write the data
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let mut data = pda_account.try_borrow_mut_data()?;
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data[..].copy_from_slice(instruction_data);

The Code: Update Data with Realloc#

What if the user wants to update their data to something longer or shorter?

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let new_len = new_data.len();
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// 1. Resize the account's data buffer
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pda_account.realloc(new_len, false)?;
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// 2. Adjust the rent balance
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let required_lamports = Rent::get()?.minimum_balance(new_len);
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let current_lamports = pda_account.lamports();
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if current_lamports < required_lamports {
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    // Data got BIGGER: User needs to pay more rent
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    let diff = required_lamports - current_lamports;
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    invoke(
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        &system_instruction::transfer(user.key, pda_account.key, diff),
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        &[user.clone(), pda_account.clone(), system_program.clone()],
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    )?;
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} else {
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    // Data got SMALLER: Refund the excess rent to the user
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    let diff = current_lamports - required_lamports;
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    // Since our program owns the PDA, we can directly modify its lamports
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    **pda_account.try_borrow_mut_lamports()? -= diff;
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    **user.try_borrow_mut_lamports()? += diff;
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}
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// 3. Write the new data
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pda_account.try_borrow_mut_data()?.copy_from_slice(new_data);