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Examples7. Share a treasury

7. Share a treasury

Alice and Bob want a shared wallet. Neither wants to email a private key. So the key becomes a Rewall secret. Alice funds the wallet, stores its key and grants Bob. Bob reads the key into memory and spends from it. Nobody pastes a key anywhere.

This runs on Sepolia, a test network, with test tokens. Do not use real money or real credentials.

Who is involved

  • Alice, rewall-test-1.eth, wallet 0. She funds the treasury and stores its key.
  • Bob, rewall-test-2.eth, wallet 1. He reads the key and spends.
  • The treasury, wallet 7, with no name. It holds the balance and is never used directly.
  • A stranger, wallet 2, with no name. Tries to read and fails.
  • Cold storage, rewall-test-3.eth, wallet 3. Recovery on the secret.

The secret is treasury.rewall.rewall-test-1.eth, with rewall.type set to privkey. Money moves on the same rail as example 6.

Step by step

Fund the treasury. Transfers.held(TOKEN) checks the treasury’s balance on the rail. If it is below AMOUNT, Alice pays it. First she checks she holds at least twice AMOUNT, then Transfers.pay(treasury.address, TOKEN, 2n * AMOUNT) moves that across. This is a private transfer on the rail, so it is not a chain transaction. If Alice has nothing, the script stops with the same funding advice as example 6.

Store the key as a secret. alice.create stores the treasury’s private key, taken from treasury.getHdKey().privateKey and encoded with toHex. The options are type: "privkey", grantees: ["rewall-test-2.eth"] and recovery: ["rewall-test-3.eth"]. The data key is wrapped for Alice, Bob and cold storage. There is no overwrite, so a second run gets SecretExistsError and reuses what is there. Rewriting would hand every reader a new wrap for no reason.

Bob reads it. bob.get(SECRET) returns the hex key as bytes. privateKeyToAccount from viem rebuilds the account from it, in memory. Bob never had the key before, and it is never written to his disk.

Bob spends. A Transfers built on the rebuilt account calls held, then pay(wallet(1).address, TOKEN, AMOUNT) to send to Bob’s own wallet, then held again. The treasury signs the EIP-712 request that authorises the transfer. That is the only thing it ever does.

A stranger cannot. stranger.get(SECRET) fails with NoWrapError.

What to notice in the output

The first line is the treasury’s balance. Then either Alice stored the treasury key and granted rewall-test-2.eth or, on a second run, treasury.rewall.rewall-test-1.eth already holds the key. Then Bob opens the treasury, and the script prints its address, followed by the balance before and after his spend. The stranger fails last.

The treasury wallet at index 7 is never used directly by anyone. It signs from inside Bob’s process, and only because Bob could open the secret.

Why this is different from sending someone a key

A key you send is a key you cannot take back. It sits in a chat log or a password manager forever, and you have no idea how many copies exist.

Here the key lives in one place, encrypted, wrapped for exactly the people who should have it. Adding a signer is a grant. Removing one is a rotation. revoke makes a fresh data key and a fresh blob, and the removed wrap stops working.

That does not unlearn the key from anyone who already opened it. That is the same caveat as example 3. A signer who leaves still knows the treasury key. So the real fix is a new treasury key, and rotate accepts a new plaintext for exactly that. What Rewall gives you is a list you control and can change, rather than a secret you have lost track of.

Why the treasury never needs gas

Gas is the fee for a chain transaction. The treasury never sends one. It only signs, off chain, to authorise transfers on the rail. The one leg that costs gas is redeeming a withdrawal ticket, pnpm run redeem <ticket> in rail/, and whoever redeems pays that themselves. So a shared wallet can hold a balance without anyone topping it up with ether.

What is private and what is public

Private:

  • The treasury’s balance and every transfer from it. Those live in the rail’s ledger, off chain.
  • The key itself, encrypted in rewall.blob.

Public:

  • That treasury.rewall.rewall-test-1.eth exists and holds a privkey.
  • That rewall-test-2.eth is on its rewall.grantees list.
  • The deposit that put tokens into the vault in the first place, with its amount.
  • The treasury’s address, to anyone who can open the secret. The script prints it.

Run it

The rail must be running. See the rail page for how to start it. Alice needs a balance on the rail of at least twice AMOUNT. Example 6 explains how she gets one, and this example draws on the same balance.

cd examples
pnpm run 07

Run it twice. The second run finds the secret already there and reuses it.

Next: 8. Grant a machine.

6. Pay a name8. Grant a machine