Privacy

Local mode's only network call downloads the list of pre-built rosters, at most once a day. Cloud mode stores rosters and draft state on the rostr API; tasks and repo names are encrypted on your machine before they're sent.

Data

Data	Local	Cloud (server)
Rosters	Disk	Plaintext
Drafts (member, session ID, timestamps)	Disk	Plaintext. Session IDs are random
Tasks	Disk	AES-256-GCM ciphertext
Repo identity (owner/repo)	Disk	HMAC-SHA256 fingerprint + AES-256-GCM ciphertext
rostr key	—	Never transmitted

Keys

The CLI derives three independent keys from your rostr key. Only the auth token leaves your machine.

rostr key
  ├─ HKDF-SHA256(info="auth")        → auth token
  ├─ HKDF-SHA256(info="encrypt")     → encryption key
  └─ HKDF-SHA256(info="fingerprint") → fingerprint key

Auth token: bearer credential for the API. The server stores only its SHA-256 hash.
Encryption key: encrypts tasks and repo names with AES-256-GCM, with a random 96-bit nonce per value.
Fingerprint key: HMAC-SHA256 over owner/repo, so the server can match project links without learning repo names.

Distinct HKDF labels make the keys independent: none reveals the rostr key or any other derived key.

What the server sees

Visible: roster contents, which members are drafted and when, session IDs, repo fingerprints, and the size and timing of task ciphertext.
Not visible: your rostr key, task plaintext, repo names, prompts, or code.

Consequences

No recovery. A lost key means your cloud data is unrecoverable, by you or by us.
API responses contain task ciphertext. rostr stats --json decrypts it for you.
Cloud environments need ROSTR_KEY to decrypt tasks. Never commit it.