This page explains exactly how Brikwall protects your files, who it protects them from, and where that protection ends. The encryption runs in a small core written in Rust, the same code on every phone.
| Who | What they can do | What Brikwall does |
|---|---|---|
| Casual snoop | Picks up your unlocked phone | Shows only a pattern pad. Locks on leaving, blocks screenshots, limits attempts, can disguise itself and photograph them. |
| Coercer | Forces you to unlock | Decoy vaults and a duress pattern. Nothing shows how many vaults exist. |
| Forensic examiner | Has a full copy of storage, maybe the phone too | A copy alone can't test guesses (hardware key). On the phone, each guess costs a chip operation plus Argon2id. Files don't reveal vault count, sizes or ownership. |
| Backup holder | Has your backup file (for example, Google) | Backups only open with the 128-bit recovery phrase, never with the pattern alone. |
| Malware or root on an unlocked phone | Reads memory while the vault is open | Out of scope for any app. We limit exposure: keys are wiped on lock and no plaintext is written to disk. |
Your pattern goes through the phone's security chip first, then through a memory-hard function. The chip step is what stops offline guessing; the Argon2id step makes each guess expensive.
// 32 random bytes made at setup (not secret)
device_salt = random(32)
challenge = SHA-256("…/hw-challenge" ‖ device_salt ‖ pattern)
// HMAC with a key that can never leave StrongBox / the secure environment
hw_tag = HMAC-SHA256(chip_key, challenge)
master = Argon2id(pattern, secret = hw_tag, salt = device_salt,
memory = 128 MiB, passes = 3, lanes = 1)
slot_key = HKDF(master, "…/slot/pattern/key")
// the pattern and anything that verifies it are never storedCompare: many vault apps use PBKDF2 with a salt anyone can read, so a copy of the files can be attacked on a fast computer. Brikwall's chip step means a copy can't be attacked at all without the phone.
pattern ──► master ──► pattern slot ──┐
recovery phrase ──► recovery slot ────┴──► vault key (random, per vault)
└─► index (new random key on every change)
└─► each file's own random key
└─► 64 KiB chunks, AES-256-GCMfl/device.bin salt + settings 49 bytes
fl/keys/<32 hex> slots, roots, dummies every file exactly 1,024 bytes
fl/objects/<32 hex> encrypted chunks every file exactly 65,568 bytesFive free misses, then 30 seconds, doubling with every miss up to one hour. The deadline is measured on a clock that changing the time can't move. Restarting the phone restarts a wait that's already running, but doesn't reset the count. Only a correct pattern resets failures.
Patterns need 7 to 25 dots. Passing straight over a dot includes it, the same as Android's lock screen.
Drawing the duress pattern opens its decoy vault, and in the same moment:
Because the hardware key is gone, old key slots that flash memory may still hold can't be opened, even by someone who later learns your pattern.
The 12-word phrase (128 bits) goes through Argon2id without the hardware step, on purpose, so it still works on a new phone after the old one is lost. It opens a separate recovery slot. After recovering, you set a new pattern and the old pattern slot is deleted.
A backup file is a byte-for-byte copy of the already-encrypted store, with a checksum. Restoring accepts only the expected file names and sizes, checks the whole file in a staging folder, and only then swaps it in.
The only connection Brikwall makes is to RevenueCat, to verify Pro purchases from Google Play. The app's network configuration starts with an empty list of trusted certificate authorities, then trusts only RevenueCat's domains, and those must chain to pinned root certificates. Any other host fails at the handshake. Cleartext is refused, and user-installed certificates are never trusted.
RevenueCat sees an anonymous random ID, the purchase token and product, the app version, device model and language. It never sees vault contents, patterns, keys or how many vaults you have. Purchase answers are signed, and Brikwall only accepts verified ones.
Found something? Email support@brikwall.app with the steps to reproduce it. We'll reply as quickly as we can, keep you updated while we fix it, and credit you in the release notes if you'd like. Please give us a reasonable chance to ship a fix before you publish.