Hardware wallet · in design · devkit first

No battery. No port. No buttons.Just clear epoxy.

Crystal is a hardware wallet in design: a transparent flex circuit cast in a solid block of clear resin. Power and data arrive over NFC. You read every transaction on e-paper and approve it with touch pads sealed under the surface. Take it off its cradle and it is inert.

Drag to turn it over

125 × 31 mm stripboard modelled to scale from the design filesresin block, some part heights and screen content illustrative

What's inside

Every part, in plain sight.

The circuit is designed on transparent PET flex rather than the usual yellow polyimide, so through the resin you can see the coil, the touch pads and every chip on the strip. This is the devkit, with its programming tail still attached.

1
2.13″ e-paper, 250 × 122
Shows what you are about to sign. Keeps its last image with no power at all.
2
Secure element
NXP EdgeLock SE050, used only as a PIN vault with an attempt counter.
3
Touch pads
CONFIRM and REJECT, sensed through the resin by the MCU's own touch controller.
4
NFC coil
13.56 MHz, six turns on the back layer. Power and data both arrive here.
5
Programming tail
SWD, UART, reset and boot pins. Kept on the devkit; cut off before potting.
6
Display connector
The panel's flex cable lies flat into a 24-pin connector.
7
MCU
STM32U385 Cortex-M33. Firmware will run secp256k1, BIP32, BIP340 and Keccak here, in software.
8
NFC front end
NXP NTAG 5 link: ISO 15693 data plus a regulated 3.0 V harvested supply.

How it works

It runs only while you are using it.

01
Dock it
Set the wallet on a cradle, an NFC reader whose 13.56 MHz field powers it continuously and carries data. A phone held to the coil may also power it, best-effort.
02
Read it
The transaction is drawn on the e-paper: amount, destination, fee. What you see comes from the wallet, not from the computer asking.
03
Touch it
Press CONFIRM or REJECT through the epoxy. The pads are wired straight to the MCU, so no message on any bus can fake a press.
04
Lift it
Out of the field the wallet is off: no battery, no standby. The screen keeps showing its last image.

Power: Harvested from the NFC field, regulated to 3.0 V, under 40 mW. No battery or supercap.
Data: ISO 15693 (NFC-V) through the same coil, specified end-to-end encrypted to the host.
Display: 2.13″ e-paper, 250 × 122. Readable in daylight, zero power to hold an image.

Two editions

Devkit first. Sealed units after.

Release 1

for developers

Crystal Devkit

The same circuit, left un-potted so you can probe it, flash it and debug it.

Bare transparent flex, no resin. Every part can be reached with a probe.
Programming tail kept: 8 contacts at 1.0 mm pitch with SWD, UART, reset, boot and power.
Debug left open: flash, step through and test firmware over SWD.
Test points on every supply rail (V_EH, V_SYS, V_SW, GND) for power profiling.
Same coil, display, MCU and secure element as the production unit.

Not for real funds. It has no physical protection, and the flex and glass panel are fragile outside the resin.

Release 2

for holding keys

Crystal

The finished wallet: locked down, then cast in a solid block of clear epoxy.

Fully sealed in clear epoxy. No ports, no buttons, no battery.
Programming tail cut off before casting; debug permanently closed (RDP level 2).
NFC front end and secure element configuration locked at the factory.
Designed for signed firmware updates over NFC only, with anti-rollback.
Touch pads calibrated through the finished resin, per unit.

Cannot be opened or reworked. That is the point.

Security model

Trust the block in your hand, not the machine it talks to.

This is the design the hardware is built around and the firmware will be written to. The firmware itself hasn't been written yet.

Three secrets and a PIN

The seed is stored encrypted in MCU flash under KDF(PIN, MCU key, SE secret). An attacker needs the flash contents, the chip-unique key, the secure element's secret and your PIN. The secure element releases its secret only after PIN checks, behind an attempt counter.

The cradle is untrusted

Host-to-wallet traffic is specified as authenticated and encrypted end to end. The cradle supplies power and relays bytes; it can refuse service but must not be able to read or forge messages.

One interface

After potting the only way in is ISO 15693 over the coil. No USB, no Bluetooth, no debug pins. Firmware updates are designed to arrive the same way, signed, with an anti-rollback counter.

Locked before it is sealed

Production units are provisioned, read-out protected at RDP level 2 (debug closed for good) and NFC-configuration locked, then the programming tail is cut off and the strip is cast.

Nothing to open

There is no case to unscrew and nothing to pry apart. Reaching the circuit means cutting through solid resin.

Signing on the MCU

The secure element never signs. Key derivation and signatures will run on the Cortex-M33, so chain support is ordinary firmware rather than a vendor applet.

Status

Where the design stands.

Crystal is in active design and has not been released for fabrication. Parts are chosen and the circuit and board are being laid out; firmware hasn't been started. Before anything ships, test coupons have to prove the coil tuning, the secure element's peak current and touch sensing through the resin, and the resin itself has to pass qualification. There is no price or date yet; register and we'll tell you when there is.

doneArchitecture and power budget
donePart selection: MCU, secure element, NFC front end, display
nowSchematic, board layout and routing
nowTest coupons: coil tuning, touch through resin, supply peaks
nextFirmware and the host protocol
nextResin qualification and transparent-flex assembly sign-off
nextDevkit build
nextSealed production units

Questions

FAQ

Why no battery?

A sealed block can't hold a lithium cell that needs venting and charging, and nothing in the wallet needs power while it isn't in use. E-paper holds its image without power, so the last thing you approved stays on screen.

What is the cradle?

A silicone dock with an NFC reader. It powers the wallet for as long as it sits there and passes encrypted messages to and from your computer. It is a separate product that hasn't been designed yet, and what ships with each edition isn't decided. We'll share details as they firm up.

Can I use it with my phone?

Possibly, as a fallback. A phone held on the coil may be able to power the wallet and carry data, but that hasn't been tested through the resin and phone NFC output varies a lot by model. Unlocking and signing will most likely need the cradle.

Which chains will it support?

The firmware requirements cover secp256k1, BIP32, BIP340 (Schnorr/Taproot) and Keccak, the building blocks for Bitcoin and Ethereum-family chains. The supported-chain list isn't final; tell us what you need in the form.

What does the devkit not do?

It isn't sealed, so it has none of the potted unit's physical protection, and its debug port is open by design. Use it to test and debug firmware and hardware, not to hold funds you care about.

Can a production unit be repaired?

No. Once it is cast, nothing inside can be reworked. Firmware can still be updated over NFC with a signed image.

Does signing up commit me to anything?

No. There is no price or date yet. We'll email you when the edition you picked is ready to order, and that's all we'll use your address for.

Get on the list.

Tell us which edition you want. The devkit comes first; we'll write when it's ready to order, and again for the sealed unit if you picked it.

Your answers help us size the first batches and decide which chains to support first.