The Problem
Payments Belong in Signal.
Signal enables private communication for everyone, but the moment we leave Signal to make a payment, our interactions become traceable. Creating a privacy gap between our messages and our money.
Signal integrated MobileCoin to solve this, but most Signal users don't even know this feature exists. And for those who do, there's another problem: a payment system that's only used within Signal reveals you're a Signal user.
The Solution
Bitcoin + Cashu = Private Payments.
Bitcoin is the obvious choice. As the most widely adopted cryptocurrency, using Bitcoin gives Signal users plausible deniability—you can't be identified as a Signal user simply by transacting in Bitcoin.
But Bitcoin alone isn't enough. Cashu ecash, built on Chaumian blind signatures, adds the privacy layer Bitcoin lacks. With Cashu, Signal users can send and receive Bitcoin micropayments completely anonymously, natively within the app. Private messages meet private money.
See It In Action
The Signal Cashu fork demonstrates how bitcoin payments can work seamlessly inside Signal.
Users can send ecash directly in their Signal conversations, like handing over a physical bill to your friend.
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 extends this same principle to money.
Chaumian ecash ensures user privacy while enabling instant and cheap payments, even for tiny amounts. Ecash is not a cryptocurrency but a representation of an asset, just like how physical cash represents your money. No speculation, no get quick rich schemes. Cashu works best with Bitcoin but it is compatible even with fiat currencies like USD.
Blind signatures are the cryptographic primitive that enable cash-like privacy in the digital world. Introduced in the 80s by visionary cryptographer David Chaum, ecash is experiencing a renaissance in recent years due to open-source projects like Cashu.
The Cashu Signal 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 a Blind Diffie-Hellmann Key Exchange (BDHKE) to achieve unlinkability:
Bob publishes public key .Alice picks secret and computes .Alice sends to Bob with being a random blinding factor.Bob sends back to Alice blind signature .Alice can calculate the unblinded signature as .Alice can take the pair as an ecash token and can send it to user Carol.Carol sends to Bob who then checks that , and if so treats it as a valid spend.Where all upper-case symbols are elliptic curve points and is the generator point, is the mint's private key, and is a blinding factor. The mint can verify tokens without knowing who originally created them.
How It Works
Technical Overview for Developers
The Signal Cashu integration embeds a lightweight Cashu wallet directly into Signal using the Cashu Development Kit. Building with Cashu is as simple as it gets so we added Cashu to Signal for iOS and Android. The result is a beautiful and intuitive user experience.
Ecash is like physical cash and is stored locally on the user's device. To make a payment, the user sends ecash through the encrypted Signal chat, like any other text message. Nobody facilitates the payment for you, everything stays between you and your friends.
Cashu Mints issue ecash in return for payments on the Bitcoin network. Users deposit Bitcoin to a mint and the mint acts as a trusted custodian for the Bitcoin it receives. Think of it like a community bank, but with strong privacy. Mints allow users to 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. It is defined in the Cashu protocol specifications. This means that any individual or organization can run a mint or create a wallet. Cashu has a vibrant open-source ecosystem with many wallet and mint implementations and developer libraries to chose from.
Protocol Specifications
The Cashu protocol is defined by a set of open 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.
Signal Your Support
Our proof-of-concept demonstrates that Cashu Signal is technically feasible. If you like this idea as much as we do, show your support and let's spark the imagination of the open-source world.
Show Your Love For Bitcoin In Signal
For Signal Users
- Spread the word by sharing this site with your Signal contacts and on Social Media #bitcoinforsignal
- Engage with Signal by tagging and mention Signal official accounts in relevant posts
- Discuss Bitcoin For Signal topic in forums, meetups, and with your friends
For Developers
- Review the Signal + Cashu proof-of-concept code
- Build complementary tools (mint infrastructure, testing tools, etc.)
- Learn about Cashu and join the discussion.
For Decision Makers at Signal
Cashu naturally aligns with Signal's privacy first mission.
- Encrypted messages deserve encrypted money, Cashu enables truly anonymous Bitcoin payments
- Widespread Bitcoin adoption protects user privacy better than specialized cryptocurrencies
- Bitcoin brings millions of potential new users, more users means better privacy for everyone
FAQ
What is Cashu?
Cashu 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 Cashu different from MobileCoin?
Cashu is a purely open-source project with no commercial interests. It is not a speculative cryptocurrency but a protocol that works with any asset. Bitcoin is internet's native digital currency with the largest user base across the world. Cashu brings strong privacy to bitcoin, making it a pragmatic solution that Signal can build on.
Will Signal actually do this?
We love and trust Signal and want to imagine a better world together with them. This site and the proof-of-concept are tools to spark their imagination and to show Signal that there's real interest for global micropayments within their ecosystem. Together with Signal, we would love to start a discussion about integrating Cashu or a similar bitcoin privacy solution.
How can I help?
Share this site, try the proof-of-concept fork. The best support you can give is to use privacy-preserving technologies and to share it with your friends. If you're a developer, check out the Cashu protocol, consider integrating it with your app, or contribute to the Cashu code or the broader Cashu ecosystem directly. To support the open-source developers working on Cashu, consider supporting our non-profit OpenCash.