A few blank cards
This Amazon listing names the dual interface and the default SCP02 keys. A few cards are enough to try the protocol with a phone or a desk reader.
- Packs of 2 or 5
- About $9 a card
- Ships from Amazon
OPEN NFC PROTOCOL / DRAFT 2.1
Cashu,
now on a card.
Wallets load ecash onto the card. Terminals can accept a tap offline, then settle with the mint when connected.
THE FILM / 0:48
How it works
The film as text
- Card. The Cashu Card is an NFC smart card that runs an open protocol.
- Key. The card makes its key on the chip, and the key stays there.
- Load. A wallet writes eight pieces of ecash into the card's 128 slots.
- Tap. The till is offline. It selects the card and names the pieces for a 21 sat bill.
- Sign. The card signs once for the whole payment and burns the pieces it signed for.
- Settle. The till accepts the payment offline. Later, it settles with the mint.
ONE TAP / SIX STEPS
One tap, step by step
The customer holds the card to the back of the merchant's phone, and the phone selects the Cashu Card applet.
The phone reads the card's pieces and names the ones it wants for a 21 sat bill: 1, 4 and 16 sat.
The phone sends the outputs it will swap those pieces for at the mint.
The card signs once for the whole payment and burns each piece it signed for.
The phone checks the mint's signature on each piece offline, then accepts the payment. Until it settles, the merchant carries the risk that a piece was spent elsewhere.
The card leaves the phone. Later, back online, the phone swaps the pieces at the mint and the payment settles.
CARDS / NXP J3R180
Where to get cards
The Cashu Card applet runs on NXP J3R180 cards (JCOP 4, Java Card 3.0.5) with contact and contactless interfaces. Buy them unfused and initialized, with the default GlobalPlatform keys, and the install guide takes you through installing the applet.
Blank cards by the hundred
Two suppliers list dual-interface J3R180 cards for volume orders. CardLogix quotes larger orders from California, and Feitian publishes its price breaks on Alibaba.
CardLogix$11.95 a card list price, with volume quotes. Ships from California.Get a quote
Feitian on Alibaba$7.89 a card from 100 and $5.69 from 500. Sold from Beijing.See it on Alibaba
Prices are as listed on 23 October 2026.
Cards with your design
Your artwork goes on J3R180 cards, and each card ships with the Cashu Card applet installed and tested. Prices per card are set to compete with the blank cards above.
- Choose a quantity and pay.
- Send your artwork.
- Approve a printed proof.
- Cards ship with the applet installed.