Two money systems in one app
A regulated euro account (SEPA top-up, IBAN details, PDF statements) next to on-chain assets such as EURC and BSO. Send to an IBAN, a BlockBen ID or an Ethereum address from the same screen.
Case study · BlockBen
A euro account and a crypto wallet, without passwords.
BlockBen keeps a regulated euro account and on-chain assets behind a single login. There are no passwords: every sensitive action is signed on the phone with a key share. We built the app for Android and iOS, in Flutter.
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- Platform
- Android and iOS, Flutter
- Field
- Fintech, euro account and digital assets
- Languages
- Hungarian, English, Latvian
- Partnership
- 5+ years
- 0passwords: logging in is a cryptographic signature from the device
- ~35sensitive operations, each signed on the phone
- 22role types for delegated access, including corporate and fiduciary
- 3languages, about 4,000 strings each
The challenge
A bank account and a crypto wallet, behind a single login
BlockBen brings two money systems that are usually kept apart into one app. That takes security that holds up in a banking app, and a simplicity that is rare in a crypto wallet.
Two money systems, two worlds
A bank account and a crypto wallet usually live in two separate apps, with different rules, interfaces and security models.
The password is the weakest link
Phishing, reused passwords: in a finance app, a single stolen password is one too many.
Regulatory expectations
Identity verification, proven wallet ownership, delegated access: compliance has to be part of the app, not a layer added later.
The usual approach
A single key, or a third-party MPC SDK.
That is how most fintech apps protect the account. In BlockBen, the key is split into shares across several devices.
The solution
A purchase in five steps, every step signed
From log-in to a finished transaction: the user sees a simple flow, while the phone signs every sensitive step in the background.
Real screens from the app, taken with a test account. Account and receipt numbers are replaced with zeros.
Step 01: Log in without a password
The registered device signs a one-time server challenge. There is no password, so there is nothing to phish.
Step 02: One balance, every account
Euro and tokens on one screen, combined per asset across all accounts.
Step 03: Review before confirming
Amount, exchange rate and fee calculated live, then a swipe to start. No surprises at the end.
Step 04: Signed on the device
The phone signs the transaction with its own key share, and every step can be followed.
Step 05: A visible signature
Every transaction shows its cryptographic signature and signed hash. Security that isn't hidden, but verifiable.
Features
Banking-grade compliance and crypto flexibility, in one app
Everything below is implemented in the app's code, not just planned.
No passwords, QR login on the web
Each install generates its own key pairs. To log in on the website, scan the QR code and the phone signs you in.
Every sensitive action is signed
Transfers, permission changes, device management: each signature is bound to the exact operation and the acting person, and can't be reused.
Encrypted device pairing
Adding a new phone moves your keys encrypted end to end. The server relays them but can't read them.
Proven wallet ownership
An external wallet (MetaMask and others, via WalletConnect) is only trusted after an EIP-712 signature proves it's yours.
Delegated access
Your accountant can only view, your partner can also pay. Rights are set per feature, with expiry and instant revocation.
Built-in identity verification
KYC with document check, liveness selfie and questionnaires, for personal and business customers. Features unlock after verification.
Security
The key isn't in one place. It's split into shares.
No single secret protects the account. Each device derives its own key share, signatures are combined from the shares, and the phone keeps its share under layered encryption.
Threshold cryptography
BLS12-381 threshold signatures with distributed key generation, running natively on the phone. Built in-house, not a third-party MPC SDK.
Verifiable key distribution
Every key share arrives with a mathematical proof. A bad or tampered share is rejected before it is used.
Layered encryption on the device
An encrypted local database with key shares encrypted again field by field; wrapping keys live in the iOS Keychain and Android Keystore.
Hardening
PIN lockout checked against network time, strong biometrics only, a 9-minute session, and no start on rooted or jailbroken devices.
One of the most reliable teams I've ever worked with. Beautiful interfaces, mobile clients polished and animated to perfection.
StockLock
Token locking with tiers, inside a banking app.
With StockLock, users lock BSO tokens, climb tiers and earn rewards in several assets, in the same app that holds their euro account.
- Six tiers up to a gold Legend tier: reward multipliers up to 1.5x, fee discounts, early access and exclusive events
- Active, unlockable and past locks, with rewards per lock arriving in four assets
- The app calculates and shows the consequences of an early unlock in advance
- Available after identity verification, inside a regulated banking app
Engineering quality
What sits under the screens.
We built the BlockBen mobile app in Flutter, from one codebase for Android and iOS, in a partnership of more than five years. In a finance app, code quality is a security question in itself.
Consistent architecture
94 BLoCs on one shared base, centralised typed error handling, and one screen contract across the whole app.
Generated, type-safe code
126 immutable state and data classes, 96 type-safe REST endpoints and a typed SQL layer, all generated.
Audited release pipeline
Secret scanning, tests, parallel Android and iOS builds, then an automated audit of the built app. Production builds are obfuscated.
Three languages, fully translated
Hungarian, English and Latvian, about 4,000 strings each, with nothing left untranslated.
New assets without an app update
Available assets come from the server, so launching a new token doesn't need an app release.
A polished, animated interface
Dark and light screens, live fee calculation, swipe-to-start transactions: security that doesn't cost usability.
The same process as on every project
Our process in detail- 01
Business and technical discovery
- 02
Specification and solution design
- 03
Iterative development
- 04
Testing and rollout
- 05
Long-term support
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