Security

casty has not been audited. This page lists what it holds and what each piece can do.

Secrets

Secret	Where it is	What it can do	How to take it back
Seed phrase	In memory while casty init or casty key revoke runs; never written to disk or sent anywhere. With casty init --fid and a key added from the page by a wallet, casty never sees it at all	Everything: it holds the custody of your fid	casty cannot. Keep it offline
App key (Ed25519)	~/.config/casty/keys.enc.json, encrypted with scrypt and XChaCha20-Poly1305, mode 0600	Sign casts, reactions and follows for your fid until it lapses unused (30 days by default, at most 90)	casty key revoke <key> with the seed phrase, or --self with the key itself
Signed KEY_ADD not yet confirmed	In the same encrypted store, until casty init sees the key listed or the node refuses the message	Add that one key, once	casty key revoke if it ever merges
Key store passphrase	Typed at a hidden prompt	Decrypt the app keys on this machine	Revoke the keys, delete keys.enc.json, run casty init
casty web token	~/.config/casty/web-token, mode 0600; in the paired browser’s storage	While casty web runs: read the feed and write with your app key, from wherever the page is reachable	Stop casty web, then start it with --new-token
The same, on the node’s host (1-node.sh serve)	~/snapchain/casty/config/keys.enc.json (0600), the passphrase in ~/snapchain/casty/passphrase (0600, a Docker secret), the token in ~/snapchain/casty/config/web-token; the key decrypted in the service’s memory while it runs	Read and write as you from any network, while the service runs; root on the host has the key	casty key revoke <key> with the seed phrase; docker compose stop casty on the host; --read-only keeps the key at home
Push key pair and subscriptions (casty serve)	~/snapchain/casty/config/vapid.json (0600) and cache/push.json on the host	Send a push, “new mention from @name”, to the subscribed browsers; the push service sees only ciphertext	Delete both files and restart casty; turn notifications off in the browser
Cloud token (HCLOUD_TOKEN, AWS credentials)	Your environment; the scripts never write it	Create and delete servers in that account	Revoke it in the provider’s console
SSH key	Yours; only the public half is uploaded	Log in to the node host with root rights	Remove it from the host and the provider

A seed phrase controls the whole account. Use a test account for this tutorial, paste a seed phrase only into software from developers you trust, and prefer a key authorised by your wallet: casty init --fid <fid>, then casty web and, under you, “add a key with your wallet”.

The seed phrase prompt reads from the terminal with echo off. With --mnemonic-stdin the phrase comes from a pipe instead, and the passphrase prompt still reads the terminal. casty zeroes the bytes of the phrase after use; the string handed to the key derivation library, and the key it derives, cannot be cleared from memory in JavaScript.

CASTY_PASSPHRASE replaces the passphrase prompt. It exists for tests and pnpm demo; do not use it for a key store that holds a real key.

What is reachable

• On a rented host, the firewall opens SSH (22), the HTTP API (3381) and gRPC (3383) to --allow-ip only, your own address by default. Gossip (3382) is open to everyone so other nodes can connect. A host you already have gets no firewall from casty.
• statsd (8125/udp, 8126/tcp) and Grafana (3000) are published on the host’s loopback only, statsd through the compose file’s own STATSD_PUBLISH variables in .env, Grafana through the override. Grafana’s admin password is the random one .env records; viewing needs no login, as Snapchain’s grafana.ini has it.
• casty talks to your node through the SSH tunnel at 127.0.0.1:3381. It calls no hosted Farcaster API. The public fname registry at fnames.farcaster.xyz is asked only for a name the node does not know: an @name you follow or mention in a cast (--no-allow-fname-server turns that off), read with feed --fids or look up in casty web, and the author of a cast you name by its farcaster.xyz link. An OP Mainnet RPC is asked only when you pass --op-rpc.
• casty web listens on 127.0.0.1 unless --listen names another address, and every API request to it needs its token. In a browser and on a phone lists how the page is protected, and what changes when a phone reaches it over the local network.
• 1-node.sh serve --domain opens the page to the internet over HTTPS (80 and 443, opened with 0-provision.sh --https); --tailscale only to your tailnet. The page then needs its token, sends HSTS, and answers one address at most 120 API requests a minute. From any network lists what the host holds.
• Casts from other people may contain terminal escape sequences. casty removes control characters and bidirectional overrides before printing them, and the web page inserts cast text as text.

If something leaks

• An app key: casty key list shows what is registered to your fid. Revoke the key with casty key revoke <key> --self from a machine that still has it, or with the seed phrase from anywhere.
• The seed phrase: move the fid to a new custody address with a wallet you trust, then revoke every app key.
• A cloud token: revoke it, then look for servers in the account that you did not create.
• The casty web token: stop casty web and start it again with --new-token. Every link printed before stops working. On the node’s host: delete ~/snapchain/casty/config/web-token and docker compose restart casty.
• The node’s host: revoke the app key with the seed phrase, delete ~/snapchain/casty, and treat the host as compromised for the node too.

Reporting a problem

Report vulnerabilities privately through the repository’s security advisories, not in a public issue. The repository’s SECURITY.md carries the same table.