Equalis

The problem

Native notes apps are only as private as the phone passcode, a paired computer or the cloud account behind them. Face and fingerprint unlock do not stop someone who already knows the passcode, because the passcode opens the same doors.

Many people share a passcode with a partner or family member, hand their unlocked phone to someone, or have typed it in front of others. For them, the notes app is the least private place on the phone, even though it is where they keep their most private text: passwords and codes, personal notes, a few photos.

The idea

Equalis installs as a normal, fully working calculator — on the home screen it is simply "Calculator". At setup you choose a 4–6 digit code. Type the code and press =, and the calculator opens a notes app with rich notes, folders and photos. A wrong code behaves exactly like an ordinary calculation.

• A calculator first. Correct operator precedence, exact decimal arithmetic, a pull-down history and three themes: Graphite, Paper and Midnight.
• No account and no cloud. Notes, folders and photos stay on the phone.
• Encrypted on the device. The whole notes database is encrypted, with a key that depends on your code and on a secret held in the phone's secure hardware, so a copied file is useless.
• Your code only. Face or fingerprint unlock cannot open the notes, and knowing the phone's passcode is not enough. Repeated wrong codes silently pause code entry.
• Recovery without a server. A forgotten code is reset through three security questions on the same phone. Without the code or the answers, nobody can open the notes — including me.

How I'm building it

I am designing and building Equalis end to end: the product rules, the calculator and notes UI, the security architecture, the native code and the website.

Security architecture. The design starts from an honest threat model: people nearby who know the phone passcode, not forensic labs or malware, and the product says so plainly.

• A custom native module in Swift and Kotlin runs Argon2id key derivation and keeps secrets in the iOS Keychain and Android Keystore (StrongBox where available), excluded from backups and device transfers.
• The notes database uses SQLCipher, and the app refuses to open it unless it can prove it is encrypted.
• The code is never stored, hashed or checked anywhere except by unwrapping the encryption key, and every = looks and takes the same time whether it is a sum, a wrong code or the right one.
• No runtime permission prompts: photos come from the system picker with location data removed.

App. Expo and React Native with Skia rendering for the calculator, exact arithmetic with decimal.js, and a block editor for headings, lists, checklists, quotes, callouts and code. Every decision is recorded as an architecture decision record before it lands in code.

Business model

Free covers up to 4 notes, 2,000 characters per note and 1 photo per note, with folders and search included. Pro is a one-time purchase that removes these limits — no subscription.

Status

In development. Android comes first, with iPhone to follow.