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casty

Wallets and keys

casty touches two keys. The custody address, an Ethereum account that owns your fid, signs one thing: the request for an app key. The app key, an Ed25519 key casty makes, signs everything else: casts, reactions, follows. This page says how that works.

The two keys

Section titled “The two keys”
What Where it lives When it is used
Seed phrase Nowhere: typed once into casty init or casty key revoke, zeroed after use To derive the custody address and sign the key request, or a revocation
App key ~/.config/casty/keys.enc.json, scrypt and XChaCha20-Poly1305, mode 0600; on the node’s host too with 1-node.sh serve Every message; lapses after its TTL without use (30 days by default, at most 90), and every message renews it
Key store passphrase Typed at a hidden prompt, or a Docker secret on the host To open the store

casty init derives the custody account from the phrase (--address-index picks another account of the same phrase), asks the node which fid it holds, makes the app key, has the custody account sign the key request (EIP-712 typed data, as @farcaster/core builds it) and sends the KEY_ADD message through the node. No transaction, no gas, no API key. casty key list shows every key the node lists for your fid; casty key revoke removes one, with the phrase or, with --self, with the key itself. The page under “you” shows the keys, warns a week before this casty’s key lapses, and adds a key with the wallet in the browser (below).

Add a key with a wallet

Section titled “Add a key with a wallet”

The custody signature is ordinary EIP-712 typed data, so anything that signs typed data for the custody address can authorise an app key: a wallet app, a hardware wallet behind one, a browser extension.

Under you, “add a key with your wallet”: casty makes the Ed25519 key and the two typed-data messages, the page hands them to the wallet in the browser (eth_signTypedData_v4 over EIP-1193: MetaMask, Rabby, Rainbow and the others, a Ledger behind any of them), the wallet signs with the custody address, casty checks both signatures against that address, sends the KEY_ADD through the node and stores the key. The seed phrase never leaves the wallet, and casty never sees it. casty init --fid <fid> sets up with no phrase and no key, for the page to add the first one. The terminal flow stays for an account whose custody is a bare recovery phrase and nothing else. In a browser and on a phone has the steps.

  • On a phone with no wallet in the browser, the page offers to open itself inside MetaMask, Coinbase Wallet or Trust Wallet, pairing included; wallets that announce themselves (EIP-6963) are found side by side; a wallet on the wrong account is asked to let you pick. WalletConnect, a dependency and a relay run by someone else, was left out on purpose.
  • An account whose custody is the recovery phrase farcaster.xyz gave it imports that phrase into one of those wallets once; from then on the wallet signs and the phrase is typed into nothing of casty’s.

Verified addresses

Section titled “Verified addresses”

The protocol carries VerificationAddAddress messages, an account’s proof that it owns an Ethereum or Solana address, and the node answers verificationsByFid. A profile on the page lists them, each a link to its explorer and a copy; yours are under you too. Reading them costs nothing and asks no third party; nothing is read from a chain.

How long a key lives

Section titled “How long a key lives”

A gasless key lapses after its TTL without use, and every message it signs renews it. casty never posts in your name to keep a key alive; the page warns a week ahead, and casty init --ttl 90d is the longest the protocol allows.

What casty leaves out

Section titled “What casty leaves out”
  • Payments, tips and swaps. Each needs a chain RPC, a funded wallet and chain state, which casty keeps off its path on purpose (see Security). A verified address on a profile can be copied into a wallet you trust.
  • WalletConnect. It would add a dependency and a relay run by someone else; wallets in the browser and the wallet apps’ own browsers cover the same ground.
  • Passkey pairing and the OS keychain. The page pairs with a 256-bit token that travels in the link’s fragment, and casty web asks for the passphrase once per start.