Client-side crypto

The coolest part of this project: the cryptography is implemented twice— once in TypeScript for the browser, once in Rust for the node — and the two implementations must agree byte for byte. This page shows why that matters and how it works.

The trick: two languages, one output

The browser builds a transaction, hashes it and signs it. The node receives the result and recomputes everything. If the frontend and backend had even one byte of disagreement in how they format the message, every transaction would be rejected.

The four crypto functions

1 · Address derivation

Identical in both languages:

1export function deriveAddress(rawPubkey: Uint8Array): string {
2  return "0x" + bytesToHex(sha3(rawPubkey).subarray(0, 20));
3}

1pub fn derive_address(public_key: &[u8]) -> String {
2    let mut hasher = Sha3_256::new();
3    hasher.update(public_key);
4    let digest = hasher.finalize();
5    format!("0x{}", hex::encode(&digest[..20]))
6}

2 · The canonical message to sign

1return [MAGIC, chain_id, from, to, asset, amount,
2            fee, priority_fee, nonce, timestamp].join("|");
3// "XCH-1|1|0xfrom|0xto|XCH|1000|1000|0|0|1722000000000"

1format!(
2    "{MAGIC}|{}|{}|{}|{}|{}|{}|{}|{}|{}",
3    self.chain_id, self.from, self.to, self.asset, self.amount,
4    self.fee, self.priority_fee, self.nonce, self.timestamp
5)

3 & 4 · Transaction hash

A subtle but test-worthy detail: the signing message uses SHA3-256 with the MAGIC prefix, while the transaction hash uses SHA-256 with the MAGIC suffix and includes pubkey + signature:

1sha256hex(format!(
2    "{}|{}|{}|{}|{}|{}|{}|{}|{}|{}|{}|{}",
3    self.chain_id, self.from, self.to, self.asset, self.amount,
4    self.fee, self.priority_fee, self.nonce, self.timestamp,
5    self.pubkey, self.signature, MAGIC
6))

Wallet storage & recovery

• Secret key is 32 random bytes (ed25519), stored as hex in localStorage.
• The wallet can be recovered from the secret key hex — import it anywhere, the address is re-derived from it.
• The demo also ships a seed tool (cargo run --bin seed) that prints 5 pre-funded demo wallets you can import.

Try it — it's the real thing

These demos use the same libraries as the actual app, so what you see is what the code does:

Cross-references

• Backend → Auth flow — the same signing proves wallet ownership.
• Backend → Transaction lifecycle — what the node does with the signature.
• Basics → Blockchain basics — refresher on hashes and keypairs.