Security model

Private by design, not by promise.

You don’t have to trust us. Sealby is private because of how it is built: there is no account, no server, and the keys never leave your devices.

The terms, explained

Four things worth knowing.

AES-256-GCM
The encryption standard used by banks and governments. 256-bit keys and a built-in integrity check, so a file that was tampered with simply refuses to open. Sealby gives every file its own key.
Secure Enclave
A non-exportable Secure Enclave key protects the device-side unlock key. Sealby combines that protection with your PIN, pattern or passphrase in the app.
Recovery phrase
Twelve words, generated on your device, that stand in for a vault’s key. Write them down once. Lose your PIN or your phone, and the phrase brings that vault back from a backup. Nobody else holds a copy.
Encrypted iCloud backup
When you turn backup on, Sealby uploads only scrambled blocks. Each block is encrypted before it leaves the phone, so iCloud stores data it cannot read, count or index.

No account, no server, no backdoor

There is nothing to sign in to, and no server holds your keys. There is no master key and no backdoor. Access depends on no one but you.

Deniable by design

Each vault sits behind its own PIN. Vaults are stored as identical encrypted blocks, with no list of them and no count, anywhere.

Recovery you control

Each vault has its own recovery phrase, created on your device and shown only to you. Keep it safe, and you can restore that vault on any device.

For the technical reader

How a file is sealed.

The whole pipeline runs on your device. Every step is a standard construction, and the byte-level format is documented in detail.

  1. 1

    Your PIN never becomes the key

    The PIN, pattern or passphrase is stretched with a memory-hard function calibrated per device, so guessing offline is slow even on fast hardware.

    Argon2id (libsodium) → key-encryption key
  2. 2

    The Secure Enclave wraps the vault key

    The vault key is wrapped by a key that lives in the Secure Enclave and is gated by the device passcode. It cannot be exported, copied or moved to another phone.

    Secure Enclave P-256 · passcode-gated
  3. 3

    One key per file

    Each vault has one random 256-bit key. Every file and note inside it is sealed under its own key, derived from the vault key and the file’s id, so no two files share a key and one exposed file key never exposes the vault.

    Vault key: 256-bit CSPRNG · file key = HKDF-SHA256(vault key, file id)
  4. 4

    AES-256-GCM, chunk by chunk

    Content is encrypted in chunks with a unique nonce each, and the metadata is authenticated with it. A chunk that was tampered with, swapped or reordered refuses to open.

    96-bit nonce = 32-bit salt ‖ 64-bit counter · 128-bit tag · authenticated header
  5. 5

    Fixed-size blocks, no index

    Encrypted output is stored as identical-looking blocks. There is no global list of vaults or files, so iCloud can count blocks but not vaults.

    Uniform block pool · no plaintext manifest · no registry
  6. 6

    Recovery sealed to a per-vault keypair

    Each vault has its own recovery keypair. The 12 words encode the private key; the public half seals a copy of the vault key. Only that vault opens, and only with those words.

    HPKE · DHKEM(P-256) / HKDF-SHA256 / AES-256-GCM
  7. 7

    Questions about the security model?

    Ask the person who built it. A human reads every message, and the cryptographic design and the file format are fair game.

    Email hello@sealby.app

What a server could see

  • That encrypted data exists, and roughly how large it is
  • When a backup last changed

What no one can see

  • Your files, photos, videos, or notes
  • Your PIN, passphrase, or encryption keys
  • How many vaults you have, or whether a hidden one exists
  • Anything readable, ever, because there is no key to hand over

Straight answers.

Can Sealby or Apple read my data?

No. Your data is encrypted on your device, and only encrypted data is ever stored or synced. There is no account, no server-held key and no backdoor. There is nothing readable for anyone to access or be forced to hand over.

What encryption does Sealby use?

Files and notes are encrypted with AES-256-GCM, each with its own key. The keys are protected by the Secure Enclave in your device and unlocked by your PIN, pattern or passphrase.

What if I lose my recovery phrase?

Then that vault depends on this phone and its PIN, pattern or passphrase alone. If you lose those too, or lose the phone, no one can recover the vault. There is no master key and no backdoor. That is the trade-off that makes Sealby readable by no one but you, so store your recovery phrase carefully.

Do you track me on this website?

Not as a person. This site sets no cookies, stores no identifier on your device and loads no third-party trackers or advertising pixels. We count page visits and App Store clicks on our own infrastructure, with no identifier of any kind, so we can see which pages and languages are useful but never who read them. Browsers that send Do Not Track or Global Privacy Control are not counted at all. Privacy is the product, so the website matches.

More: how deniable vaults work ·full FAQ ·Found a security issue? Write to hello@sealby.app.

Privacy that doesn’t depend on trusting us.

Download Sealby and keep your data unreadable to everyone but you.

Download on the App Store

iPhone & iPad · iOS 17+ · Free