Calle demos NFC tap-to-pay feature with Bitcoin ecash

The creator of the Cashu ecash protocol just made Bitcoin payments look as simple as tapping your phone against someone else’s. Calle, the pseudonymous developer behind Cashu, demonstrated an NFC tap-to-pay feature on July 7 that transfers Bitcoin-backed ecash tokens between two phones, no internet connection required.

How tapping phones moves Bitcoin

Cashu is an open-source protocol that creates ecash tokens, essentially digital IOUs backed by Bitcoin or Lightning Network deposits held at entities called “mints.” You deposit Bitcoin, you get tokens on your device. Those tokens live locally on your phone, just like cash lives in your wallet.

Near-field communication, the same tech that powers Apple Pay and contactless credit cards, allows one phone to beam those ecash tokens to another phone with a simple tap. No cell signal. No Wi-Fi. No blockchain confirmation delay. Just two devices, touching briefly, and value changes hands.

Cashu uses a cryptographic technique called blind signatures, originally conceived by David Chaum in the 1980s. The mint that issues your tokens can verify they’re legitimate without knowing who spent them or where. That’s a meaningful distinction from on-chain Bitcoin transactions, which leave a permanent, traceable record on a public ledger.

Numo and the growing Cashu ecosystem

Back on February 24, the Cashu ecosystem saw the launch of Numo, a free, open-source Android application built specifically for contactless payments using Cashu ecash and NFC technology.

Numo works by turning a merchant’s Android phone into an NFC payment terminal, no specialized hardware needed. The app emulates an NFC tag for payment requests, and compatible customer wallets can send ecash tokens directly to the merchant’s device. It’s available as an APK download.

Numo can automatically transfer received ecash to a Lightning address, so a merchant taps to receive ecash and the value flows into their Lightning wallet.

Cashu itself has been building toward this moment since Calle first introduced the protocol in October 2022. The protocol supports offline transfers through multiple channels beyond NFC, including Bluetooth and QR codes.

Why offline matters more than you think

Lightning Network brought transaction times down to near-instant and fees to fractions of a cent, but Lightning still requires both parties to be online. Cashu’s offline capability addresses this gap directly. Ecash tokens stored on-device can move between phones in environments where no other crypto payment method would function.

The tradeoff is trust. Unlike on-chain Bitcoin, where the network itself guarantees settlement, Cashu ecash requires trust in the mint that issued the tokens. If a mint goes offline permanently or acts maliciously, your tokens could become worthless.

What this means for investors and the broader market

There’s no token to buy here. Cashu operates as a pure open-source framework with no associated market-traded asset.

Disclosure: This article was edited by Editorial Team. For more information on how we create and review content, see our Editorial Policy.