The Problem
Signal integrated MobileCoin, but it hasn't seen meaningful adoption. Bitcoin is the obvious alternative.
Signal built payments into their app using MobileCoin — a privacy-focused cryptocurrency. But MobileCoin has limited liquidity, minimal adoption, and lacks the network effects that make a payment system useful.
Bitcoin is the world's most liquid, most adopted, and most censorship-resistant digital currency. But base-layer bitcoin lacks the privacy guarantees that align with Signal's mission.
What if Signal could offer bitcoin payments with privacy equal to or better than their messaging? That's exactly what Cashu ecash enables.
The Solution
Cashu Ecash + Signal = Private Bitcoin Payments
Developers have built a working fork of Signal that natively integrates Cashu ecash. This proof-of-concept demonstrates that private bitcoin payments can work seamlessly inside Signal.
Cashu is a Chaumian ecash protocol built on Bitcoin and Lightning. It provides true privacy through blind signatures — not even the mint knows who owns which tokens. Users can send bitcoin to each other with the same privacy guarantees as their encrypted messages.
This integration feels native to Signal. No clunky external wallets, no blockchain addresses cluttering your chats — just tap, send, done. Privacy-preserving. Instant. Bitcoin.
See It In Action
The Signal + Cashu fork demonstrates how private bitcoin payments can work seamlessly inside Signal. Below are demo videos and screenshots showcasing the integration.
Demo Video
Watch how seamlessly users can send bitcoin ecash tokens directly in their Signal conversations.
The UI is clean and native to Signal, making bitcoin payments feel as natural as sending a message.
Privacy Deep Dive
Why Cashu is a perfect match for Signal
Signal's mission is to protect privacy. End-to-end encryption ensures that no one — not even Signal — can read your messages. Cashu ecash extends this same principle to money.
Chaumian blind signatures ensure that when you mint ecash tokens, the mint cannot link those tokens back to you when you later spend them. This is cryptographic privacy, not just anonymity through obscurity.
No metadata leakage through Cashu mints. Bitcoin's base layer exposes amounts, addresses, and timing. Lightning is better, but still reveals payment channel relationships. Cashu tokens can be sent peer-to-peer with zero on-chain footprint and no revealing metadata.
This integration doesn't compromise Signal's privacy guarantees — it extends them to financial transactions. Your messages are private. Your payments should be too.
The Math Behind the Privacy
Cashu uses Blind Diffie-Hellmann Key Exchange (BDHKE) to achieve unlinkability:
Bob publishes public key K = kGAlice picks secret x and computes Y = hash_to_curve(x)Alice sends to Bob: B_ = Y + rG with r being a random blinding factorBob sends back to Alice blinded key: C_ = kB_Alice can calculate the unblinded key as C_ - rK = kY + krG - krG = kY = CAlice can take the pair (x, C) as a token and can send it to CarolCarol can send (x, C) to Bob who then checks that k*hash_to_curve(x) == C, and if so treats it as a valid spendWhere G is the generator point, k is the mint's private key, and the blinding factor r ensures the mint cannot correlate the blinded request with the final token. The mint can verify tokens without knowing who originally minted them.
How It Works
Technical Overview for Developers
The Signal + Cashu integration works by embedding a lightweight Cashu wallet directly into the Signal app. Users connect to a Cashu mint (which acts as a custodian for bitcoin) and can mint, send, and receive ecash tokens.
Ecash is stored locally and wallets store user balances locally on their device. When a user sends a payment, the app generates a Cashu token, and sends it as an encrypted message. The recipient's Signal app automatically detects the token and adds it to their balance.
Mints on Bitcoin enable payments through Lightning. Users can send and receive payments from anyone, anywhere, at any time. Whether its from another Signal contact, or a merchant that accepts Bitcoin.
The Cashu protocol is open and not controlled by a single entity. This means that anyone can run a Cashu mint and anyone can use any Cashu wallet. The protocol is defined in the Cashu specifications.
Protocol Specifications
The Cashu protocol is defined by a set of specifications called NUTs (Notation, Usage, and Terminology):
Mandatory
- • NUT-00: Cryptography - Cryptographic primitives
- • NUT-03: Swapping Tokens - Double spend protection
- • NUT-04: Minting - Token issuance
Optional
- • NUT-11: Pay to Public Key - Programmable payments
- • NUT-12: DLEQ Proofs - Discrete Log Equality proofs
- • NUT-16: Animated QR Codes - Dynamic QR codes
- • NUT-22: Blind Authentication - Privacy-preserving authentication
Complete specifications and implementation details available in the Cashu NUTs repository.
Take Action
This proof-of-concept demonstrates that Cashu + Signal is technically feasible. Now we need to show Signal that there's demand for this integration.
For Signal Users
- Share this site with your Signal contacts and on social media
- Contact Signal support and express your interest in bitcoin payments
- Advocate for privacy-preserving bitcoin integration in Signal forums
For Developers
- Review the Signal + Cashu proof-of-concept code
- Help refine the UX and security model
- Build complementary tools (mint infrastructure, testing tools, etc.)
- Learn about Cashu and contribute to the broader ecosystem
For Decision Makers at Signal
We believe Cashu ecash aligns perfectly with Signal's mission. This integration would:
- Replace the underutilized MobileCoin integration with the world's most liquid cryptocurrency
- Maintain Signal's uncompromising privacy standards through Chaumian blind signatures
- Attract millions of bitcoin users who share Signal's values around privacy and freedom
- Position Signal as the premier private communication and payment platform
FAQ
What is Cashu?
Cashu is a purely open-source ecash protocol that enables private, peer-to-peer bitcoin payments using Chaumian blind signatures. It's not a company, organization, or entity with financial interests — it's a free and open-source community-driven project with no single controlling entity. Cashu allows users to send bitcoin payments with the same level of privacy as physical cash, while maintaining compatibility with the broader Bitcoin ecosystem.
How is this Cashu different from MobileCoin?
Cashu is a purely open-source project with no financial backers or commercial interests. Bitcoin is the world's most liquid and widely-adopted cryptocurrency with deep infrastructure and network effects. Cashu brings strong privacy to bitcoin, making it a pragmatic alternative that Signal users are more likely to actually use.
Will Signal actually do this?
That depends on community demand. This site and the proof-of-concept are advocacy tools to show Signal that there's real interest. If enough users, developers, and privacy advocates speak up, Signal may consider integrating Cashu or a similar bitcoin privacy solution.
How can I help?
Share this site, contact Signal to express interest, try the proof-of-concept fork when it's available, and if you're a developer, contribute to the code or the broader Cashu ecosystem. The more momentum we build, the more likely this becomes a reality.