Tokenizing the Brazilian CBDC: A Hands-On Soroban Experiment
When Brazil's Central Bank announced DREX (the Digital Real), most developers waited for official SDKs. I didn't. With over two decades building blockchain infrastructure, I decided to prototype a functional DREX token on Stellar Testnet using Soroban smart contracts written in Rust. The goal was simple but ambitious: prove that a programmable CBDC could run on a low-cost, high-throughput ledger before the regulatory dust settled.
What follows is a condensed walkthrough of how I, André Dias Moreira Prol, built a working Real Digital tokenization layer—and the surprising performance numbers I captured along the way.
Why Stellar and Soroban for a CBDC Prototype
DREX's reference architecture uses Hyperledger Besu, but I wanted to test the thesis that Stellar's finality and cost profile fit retail CBDC better. The numbers are hard to ignore: Stellar settles transactions in roughly 5 seconds with fees around $0.00001, while the network has historically processed millions of operations daily without congestion spikes.
Soroban, Stellar's Rust-based smart contract platform, gave me the programmability DREX demands—account freezing, compliance hooks, and supply control—without sacrificing that speed. Rust was the deciding factor. Its memory safety and zero-cost abstractions matter enormously when you're handling sovereign money, where a single overflow bug could mint phantom currency.
I structured the prototype around three contracts: a token contract (the Real Digital itself), a permissions registry (simulating the Central Bank as issuer), and a transfer-control module enforcing KYC-style whitelisting.
Writing the Real Digital Token in Rust
The core token contract implements a fungible standard with administrative overrides. Here's the heart of the mint function:
#[contractimpl]
impl RealDigital {
pub fn mint(env: Env, admin: Address, to: Address, amount: i128) {
admin.require_auth();
Self::check_admin(&env, &admin);
let balance = Self::read_balance(&env, to.clone());
Self::write_balance(&env, to.clone(), balance + amount);
Self::read_supply(&env);
env.events().publish(
(symbol_short!("mint"), to.clone()),
amount
);
}
}
The critical design decision was the require_auth() call combined with a central-bank admin check. In a real DREX, only the Banco Central can mint—so I modeled that authority explicitly rather than allowing distributed issuance.
For compliance, I added a transfer wrapper that validates both sender and receiver against the permissions registry:
pub fn transfer(env: Env, from: Address, to: Address, amount: i128) {
from.require_auth();
Self::require_whitelisted(&env, &from);
Self::require_whitelisted(&env, &to);
Self::spend_balance(&env, from, amount);
Self::receive_balance(&env, to, amount);
}
This mirrors DREX's intermediated model, where only authorized financial institutions interact directly with the token. One lesson from my years in digital forensics: every state change must emit an event. I made event publishing non-negotiable, because auditability is the entire point of a traceable CBDC.
Deployment, Testing, and the Numbers That Mattered
I deployed to Stellar Testnet using the Soroban CLI. The full pipeline—compile to WASM, optimize, deploy, initialize—took under two minutes:
soroban contract build
soroban contract deploy \
--wasm target/wasm32-unknown-unknown/release/real_digital.wasm \
--network testnet
The optimized WASM binary came in at 8.2 KB after running soroban contract optimize. I then scripted 1,000 sequential transfers between whitelisted test accounts. The results validated my hypothesis: average confirmation was 5.1 seconds, and the aggregate transaction cost for all 1,000 transfers was less than one cent in XLM equivalent.
To stress the compliance layer, I attempted transfers to non-whitelisted addresses—all correctly reverted with clear error codes. This matters because DREX's regulatory framework hinges on reversibility and controlled access, not the permissionless freedom of public DeFi.
The biggest surprise was storage efficiency. Using Soroban's instance and persistent storage tiers deliberately, I kept state rent costs minimal—something that becomes critical at national scale. As André Dias Moreira Prol, I'd argue this cost profile is exactly what makes retail CBDC viable where Besu-based alternatives struggle with throughput economics.
Conclusion
This prototype proves that programmable sovereign money can run fast, cheap, and auditable on Soroban—a compelling alternative worth serious evaluation. If you're exploring CBDC or tokenization, clone a Soroban starter template today and build your own experiment before the standards are locked in.
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Top comments (1)
A testnet tokenization project is most useful when it makes the operational boundaries explicit: issuance authority, redemption path, audit events, and failure handling. The Rust implementation is a good place to encode those invariants before the interface makes them look simpler than they are.