Blank: Private Payment Amounts on Public Blockchains

Blank brings private payments to public blockchains.

The sender, recipient, and payment context remain publicly auditable on-chain, while the payment amount stays encrypted using Fully Homomorphic Encryption (FHE). This creates a payment system where transactions remain verifiable without exposing salaries, invoices, payroll amounts, business payments, or personal transfers to the entire internet.

Built on Fhenix CoFHE and ERC-4337 account abstraction, Blank combines encrypted value transfer, gasless onboarding, passkey wallets, conditional escrow, payroll, invoicing, and real-world payment workflows into a single platform.

Live on Arbitrum Sepolia, Base Sepolia, and Ethereum Sepolia.

Project Links

Notion Dossier — Recommended First Read
https://app.notion.com/p/3719c0ce7876801aac76e3cc83bcaf88
The full project story, architecture, buildathon progress, proof references, and judging context in one place.

Live App
https://app.myblank.app
The production frontend for testing Blank’s payment, invoice, escrow, and wallet flows.

Proof Deck
https://www.myblank.app/proof-deck
A verification deck with real screenshots, wallet actions, transaction hashes, explorer links, and end-to-end proof that the product works beyond just a demo.

Whitepaper
https://docs.myblank.app/whitepaper
The deeper technical explanation of Blank’s encrypted payment architecture, FHE design, and product system.

Blog: Why Fhenix CoFHE
https://blog.myblank.app/blog/why-fhenix-cofhe
Explains why Blank uses Fhenix CoFHE instead of treating privacy as a surface-level feature.

Brand Kit
https://brand.myblank.app/brand-kit
Shows the product identity, visual system, and design direction behind Blank.

How Judges Should Review This Submission

Start with the Notion Dossier for the full context.

Use the Live App to experience the product.

Use the Proof Deck to verify that the flows were tested with real wallets, real transactions, screenshots, and public explorer links.

Use the Whitepaper and Blog for the deeper technical reasoning behind FHE, CoFHE, and encrypted payment amounts.

What We Built During This Hackathon

For this buildathon, we built Conditional Invoices on Arbitrum Sepolia using Reineira's open settlement standard.

A payer can create an invoice and lock encrypted funds into escrow. The funds release when predefined conditions are satisfied, such as manual approval or deadline expiry.

The system is built around a pluggable resolver architecture, allowing future integrations with oracle-based conditions, milestone payments, multisig approvals, and other settlement mechanisms without modifying the core escrow contract.

The implementation was deployed and tested end-to-end on Arbitrum Sepolia using real Rabby wallet transactions and live Fhenix encryption flows.

The Core Idea

Public blockchains make every payment permanently visible.

If someone pays rent, receives a salary, sends money to family, pays a contractor, or settles an invoice, the amount becomes public forever.

Blank changes only one thing:

The amount becomes private.

Everything else remains publicly verifiable.

This preserves auditability while protecting financial privacy.

Why FHE Matters

Blank is not using privacy as a cosmetic feature.

The encrypted amount is actively used by smart contracts.

The system performs:

• Encrypted transfers

• Encrypted balance tracking

• Encrypted comparisons

• Encrypted invoice matching

• Encrypted escrow settlement

• Encrypted threshold verification

All without exposing the underlying value.

This is possible because FHE allows computation directly on encrypted data. Instead of only proving facts about values, Blank lets contracts work with encrypted values directly.

Key Features

Private Payments

Send encrypted amounts while keeping counterparties visible on-chain.

Conditional Invoices

Private invoice payments with programmable settlement conditions.

Encrypted Escrow

Funds release based on approval logic, deadlines, or dispute resolution.

Payroll

Batch salary payments with encrypted compensation amounts.

Fiat Offramp

Move funds between crypto and traditional banking while preserving amount privacy.

Proof of Balance

Prove ownership of a minimum balance without revealing the balance itself.

Creator Economy

Private tips, gifts, subscriptions, crowdfunding, and community payments.

Agent Payments

AI agents can initiate payments through delegated session-key permissions.

Technical Highlights

• Fhenix CoFHE integration

• ERC-4337 account abstraction

• Passkey onboarding

• Sponsored gas transactions

• UUPS upgrade architecture

• Storage-safe upgrades

• NonReentrant protection

• Multi-chain deployment

• Encrypted event architecture

Validation & Proof

Blank is not only a concept or pitch deck. It has been built, deployed, tested, and documented.

• 31 deployed smart contracts

• 6,553 total tests

• 343 real on-chain transactions

• Live deployment across Arbitrum Sepolia, Base Sepolia, and Ethereum Sepolia

• End-to-end wallet testing with MetaMask and Rabby

• Real screenshots of user flows, wallet actions, success states, and transaction confirmations

• Public transaction hashes available in the Proof Deck

• Full technical documentation through the whitepaper, blog, GitHub repository, and Notion dossier

The Proof Deck exists so judges do not need to trust the claim blindly. They can verify the actual product flows, screenshots, and transaction evidence directly.

Why Blank Matters

Most blockchain applications force users to choose between transparency and privacy.

Blank introduces a third option:

Publicly verifiable payments with private financial amounts.

The result is a system that remains auditable while protecting sensitive financial information, making blockchain payments practical for salaries, invoices, payroll, business transactions, creator payments, and everyday transfers.

Blank does not hide the whole transaction.

It protects the one field that creates the biggest real-world privacy problem: the amount.

• Designed conditional invoice architecture

• Implemented resolver-based settlement flow

• Integrated Reineira settlement standard

• Upgraded encrypted escrow contracts

• Deployed contracts to Arbitrum Sepolia

• Built end-to-end invoice workflow

• Added approval and deadline release logic

• Executed live Rabby wallet testing

• Generated proof deck and verification artifacts

• Completed deployment validation and transaction verification

Bootstrapped so far, with no institutional funding raised.

This week, Blank received the highest grant in the Fhenix Akindo Hackathon. We are using that validation and non-dilutive support to plan the next phase of development.

Main Goal is to make this a better product for users.

Currently grant-supported, not institutionally funded.