Feature request: Offline calculator mode for BIP39 mnemonic, xpub, and SeedQR

[maximusmaximalistus]

Feature request: Offline calculator mode for BIP39 mnemonic, xpub, and SeedQR

I would like to propose an offline calculator mode for Jade.

I tested the following setup with an uninitialized Jade DIY:

1. Connected the Jade to a phone charger and started the device.
2. Selected Options → Temporary Signer.
3. Entered the first 11 words of a BIP39 mnemonic.
4. Selected Calculate so Jade could calculate the valid final word containing the remaining entropy bits and BIP39 checksum.

At that point, my goal was to use Jade to obtain the xpub and SeedQR corresponding to that BIP39 mnemonic.

However, Jade then asked me to connect to the companion app.

Feature request

It would be useful to have a completely standalone mode where Jade could act as an offline BIP39 calculator/key derivation device without requiring a companion app.

The workflow could be:

1. User provides the entropy by entering the first 11 or 23 BIP39 words.
2. Jade calculates the valid final word(s), including the checksum and remaining entropy bits.
3. User selects the final word.
4. Optionally enter a BIP39 passphrase.
5. Jade derives and displays the corresponding xpub.
6. Jade displays the SeedQR.
7. Powering off the device destroys the temporary signer state.

The important property would be that this entire process could happen without Jade ever connecting to a computer, phone, network, or the Internet, and without permanently storing the mnemonic or passphrase.

Jade would simply use the firmware already installed on the device. All wallet entropy would be supplied externally by the user.

This would create an interesting setup for extremely paranoid/offline users:

user-generated entropy → Jade verifies/calculates BIP39 → derives wallet information → exports xpub/SeedQR → power off → state disappears

No companion software would be required for the process.

The remaining trust assumptions would primarily be the Jade hardware and the firmware running on it. A user concerned about those risks could independently verify the firmware, build/flash Jade themselves, and generate all entropy externally.

This would make Jade useful not just as a hardware signer, but also as a completely offline, stateless BIP39 calculation and wallet-export tool.

[jgriffiths]

@bitcoinhelp FYI

[bitcoinhelp]

Thanks for the request @maximusmaximalistus. I wanted to note that Jade can technically already do this, but not sure if it's the UX you desire.

1. Turn on an uninitialized Jade and select Set up Jade
2. Choose the Advanced setup path and Restore Wallet
3. Choose Calculate final word from your user-generated entropy
4. Jade asks if you want to make a SeedQR
5. When Jade asks you to connect, choose QR, and choose not to set up a PIN
6. Your Jade will be "logged" in without ever touching an app, and you'll have a SeedQR and can export the xpub/descriptor from Options
7. Once logged out, all information will be forgotten and your Jade will remain "uninitialized"
   *(you can optionally use a passphrase with the above flow as well)

I believe this covers all the above steps you were looking for, but let me know your thoughts

[maximusmaximalistus]

I found out why Temporary Signer wasn't behaving like the offline calculator mode I was expecting.

I first tested it on a Jade DIY using a T-Display-S3.

Since this device has no camera and no battery, after entering the first 11 words, choosing Calculate, and selecting the correct 12th word, Jade immediately asks for a USB or BLE connection because QR export is not available.

I also tried the Advanced Setup → Restore Wallet path and got the same result. It asks for a connection because the device has no camera.

Then I tried the same procedure on a Jade DIY using a T-Display-S3-Pro, which has both a camera and a battery.

I selected Temporary Signer, entered the first 11 words, chose Calculate, and selected the correct 12th word.

This time, Jade immediately asked whether I wanted to export the seed as SeedQR.

I could then draw the SeedQR manually, with Jade showing each step needed to reproduce it. Everything worked as expected.

After that, I could return to the main menu, where the status in the bottom-left showed Active.

From there, I could go to Options → Wallet and export the xpub and access the other wallet information.

So, on a device with a camera, Temporary Signer already works very much like the offline calculator mode I was describing.

On a device without a camera, it does not, because Jade immediately asks for a USB or BLE connection instead.

Since Jade Core has no camera, I assume its behavior will be similar to the Jade DIY on the T-Display-S3.

I had actually tried something similar on a retail Jade some time ago, and I remembered it working. When I thought about this feature again, I first tested it on the Jade DIY. When that failed, I was surprised because I remembered being able to do something like this on the retail Jade.

That is what made me test it again on the T-Display-S3-Pro, where I confirmed that the Temporary Signer workflow does indeed provide the offline functionality I remembered.