DevKeep — Security Model

In one sentence: your secrets are encrypted on your Mac with a key only you can derive, the result never touches a network, and the backup is useless to anyone without your passphrase.

Encryption

Secrets are sealed with AES‑256‑GCM using Apple's CryptoKit. GCM is authenticated encryption, so a tampered or truncated backup fails to open rather than silently returning garbage. Each backup uses a fresh random nonce.

Key derivation

When you choose a passphrase, DevKeep stretches it into a 256‑bit key with PBKDF2‑HMAC‑SHA256 at 600,000 iterations (OWASP's current guidance) over a fresh 16‑byte random salt. The salt and iteration count are stored in the bundle header, so the same passphrase opens the backup on any Mac — but the key itself is never written down. Passphrases are Unicode‑normalized before derivation so they behave consistently across machines.

Two ways to hold the key

Passphrase (recommended, portable). You choose a passphrase; the key is derived from it on demand. Nothing but the salt and iteration count is stored. Restore on any Mac with the passphrase. There is no recovery code and no backdoor — forget it and the secrets are gone.
Random key + recovery code. DevKeep generates a random key, shows you a one‑time base64 recovery code to save, and (optionally) stores a copy of the key in this Mac's Keychain for same‑machine restores. The recovery code is the portable path; the Keychain copy is convenience only.

What is stored, and where

The backup folder — you choose it. Contains the encrypted secrets bundle, copied config files, manifests, a plain‑text RESTORE.md, and a metadata file that lists paths only (never secret contents).

The Keychain (random‑key mode only) — a copy of the key, stored WhenUnlockedThisDeviceOnly, so it is never synced to iCloud Keychain.

App preferences — scan roots, exclusions, default folder, reminder cadence. Your passphrase and recovery code are never written to preferences or logs.

Bundle format

The encrypted bundle is self‑describing: a magic marker, a version, the KDF id, the salt, the iteration count, and then the AES‑GCM ciphertext. That's what lets a backup made today open on a brand‑new machine years later with nothing but your passphrase.

Threat model

The backup leaks (external drive lost, synced to a compromised cloud account). Without the passphrase it is ciphertext — no secret is exposed.
An attacker tampers with the backup. GCM authentication makes the restore fail rather than producing corrupted files.
Network interception. Not applicable — DevKeep makes no network requests of its own; the key is derived locally and never transmitted.
What it does not defend against: malware already running as you on an unlocked Mac (it can read the same files DevKeep can), or a weak passphrase. Choose a strong one — the in‑app strength meter helps.

No telemetry, by design

There is no analytics SDK, no crash reporter, and no "phone home." This isn't a privacy setting you can toggle off — the app has no networking code for it. That also makes the App Store privacy label a simple, honest "Data Not Collected."

Auditability

The plan is to open‑source the core engine — the scanning, the bundle format, and the cryptography — so the security‑critical code can be read and verified by anyone, while the polished app remains the product. A security tool should not ask for blind trust.

Found a security issue? Please email hello@skywaylabs.io.

Security model