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Build an offline, airgapped Bitcoin signing device for less than $50!

Image of SeedSigners in Mini Pill Enclosures

Project Summary

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The goal of SeedSigner is to lower the cost and complexity of Bitcoin multi-signature wallet use. To accomplish this goal, SeedSigner offers anyone the opportunity to build a verifiably air-gapped, stateless Bitcoin signing device using inexpensive, publicly available hardware components (usually < $50). SeedSigner helps users save with Bitcoin by assisting with trustless private key generation and multisignature (aka "multisig") wallet setup, and helps users transact with Bitcoin via a secure, air-gapped QR-exchange signing model.

Additional information about the project can be found at SeedSigner.com.

You can follow @SeedSigner on Twitter for the latest project news and developments.

If you have specific questions about the project, our Telegram Group is a great place to ask them.

Feature Highlights:

Considerations:

Planned Upcoming Improvements / Functionality:

Shopping List

To build a SeedSigner, you will need:

Notes:

Software Installation

A Special Note On Minimizing Trust

As is the nature of pre-packaged software downloads, downloading and using the prepared SeedSigner release images means implicitly placing trust in the people preparing those images; in our project the released images are prepared and signed by the eponymous creator of the project, SeedSigner "the person". That individual is additionally the only person in possession of the PGP keys that are used to sign the release images.

Starting with v0.7.0, the images distributed via GitHub are reproducible. This means you and others can verify the released images are byte-for-byte the same when built from source. You can contribute to this project by building from source and sharing the hash of the final images.

Instructions to build a SeedSigner OS image (using precisely the same process that is used to create the prepared release images) have been made available. We have put a lot of thought and work into making these instructions easy to understand and follow, even for less technical users. These instructions can be found here.

Downloading the Software

Download the current Version (0.7.0) software image that is compatible with your Raspberry Pi Hardware. The Pi Zero 1.3 is the most common and recommended board.

BoardDownload Image Link/Name
Raspberry Pi Zero 1.3seedsigner_os.0.7.0.pi0.img
Raspberry Pi Zero Wseedsigner_os.0.7.0.pi0.img
Raspberry Pi Zero 2 Wseedsigner_os.0.7.0.pi02w.img
Raspberry Pi 1 Model B/B+seedsigner_os.0.7.0.pi0.img
Raspberry Pi 2 Model Bseedsigner_os.0.7.0.pi2.img
Raspberry Pi 3 Model Bseedsigner_os.0.7.0.pi02w.img
Raspberry Pi 4 Model Bseedsigner_os.0.7.0.pi4.img
Raspberry Pi 400seedsigner_os.0.7.0.pi4.img

Note: If you have physically removed the WiFi component from your board, you will still use the image file of the original(un-modified) hardware. (Our files are compiled/based on the processor architecture). Although it is better to spend a few minutes upfront to determine which specific Pi hardware/model you have, if you are still unsure which hardware you have, you can try using the pi0.img file. Making an incorrect choice here will not ruin your board, because this is software, not firmware.

also download these 2 signature verification files to the same folder
The Plaintext manifest file
The Signature of the manifest file

Users familiar with older versions of the SeedSigner software might be surprised with how fast their software downloads now are, because since version 0.6.0 the software image files are now 100x smaller! Each image file is now under 42 Megabytes so your downloads and verifications will be very quick now (and might even seem too quick)!

Once the files have all finished downloading, follow the steps below to verify the download before continuing on to write the software onto a MicroSD card. Next, insert the MicroSD into your assembled hardware and connect the USB power. Allow about 45 seconds for our logo to appear, and then you can begin using your SeedSigner!

Our previous software versions are available here. Choose a specific version and then expand the Assets sub-heading to display the .img file binary and also the 2 associated signature files. Note: The prior version files will have lower numbers than the scripts and examples provided in this document, but the naming format will be the same, so you can edit them as required for signature verification etc.

Verifying that the downloaded files are authentic (optional but highly recommended!)

You can quickly verify that the software you just downloaded is both authentic and unaltered, by following these instructions. We assume you are running the commands from a computer where both GPG and shasum are already installed, and that you also know how to navigate on a terminal.

You must run the following verification before opening or mounting the .img file. Some operating systems modify the file on mount causing verification to fail.

Step 1. Verify that the signature (.sig) file is genuine:

Run GPG's fetch-keys command to import the SeedSigner projects public key from the popular online keyserver called Keybase.io, into your computers keychain.

gpg --fetch-keys https://keybase.io/seedsigner/pgp_keys.asc

The result should confirm that 1 key was either imported or updated. Ignore any key ID's or email addresses shown.

SS - Fetchkeys-Keybase PubKey import with Fingerprint shown (New import or update of the key)v3-100pct

Next, you will run the verify command on the signature (.sig) file. (Verify must be run from inside the same folder that you downloaded the files into earlier. The *'s in this command will auto-fill the version from your current folder, so it should be copied and pasted as-is.)

gpg --verify seedsigner.0.7.*.sha256.txt.sig

When the verify command completes successfully, it should display output like this: <BR> SS - Verify Command - GPG on Linux - Masked_v4-100pct
The result must display "Good signature". Ignore any email addresses - only matching Key fingerprints count here. Stop immediately if it displays "Bad signature"! <BR>

On the last output line, look at your rightmost 16 characters (the 4 blocks of 4).
Crucially, we must now check WHO that Primary key fingerprint /ID belongs to. We will start by looking at Keybase.io to see if it is the SeedSigner project 's public key or not.

<details><summary> About the warning message:</summary> <p> Since you are about to match the outputted fingerprint/ID against the proofs at Keybase.io/SeedSigner, and thereby confirm who the pubkey really belongs to-, you can safely ignore this warning message: 
> WARNING: This key is not certified with a trusted signature!  
> There is no indication that the signature belongs to the owner.
</p> </details> <br> <details><summary> More about how the verify command works:</summary> <p> The verify command will attempt to decrypt the signature file (sha256.sig) by trying each public key already imported into your computer. If the public key we just imported (via fetch-keys), manages to: (a) successfully decrypt the .sig file , and (b), that result matches exactly to the clear-text equivalent (.sha256) of the .sig file, then its "a good signature"!

Crucially, we must still manually check who exactly owns the Key ID which gave us that "Good signature". Thats what the warning message means- Who does the matching key really belong to? We will start by looking at keybase.io to see if it is "The SeedSigner project"'s public Key or not. Note that it is the file hashes of .sig and .sha256 that verify compares, not their raw contents.

</p> </details> <br>

Now to determine who the Public key ID belongs to: Goto Keybase.io/SeedSigner
<BR> SS - Keybase Website PubKey visual matching1_Cropped-80pct

You must now manually compare: The 16 character fingerprint ID (as circled in red above) to, those rightmost 16 characters from your verify command.

If they match exactly, then you have successfully confirmed that your .sig file is authentically from the SeedSigner Project! <BR>

<details><summary>Learn more about how keybase.io helps you check that someone (online) is who they say they are:</summary> <p> Keybase.io allows you to independently verify that the public key saved on Keybase.io, is both authentic and that it belongs to the organization it claims to represent. Keybase has already checked the three pubkey file locations cryptographically when they were saved there. You can further verify the key publications if you would like:

Once you have used one of these methods, you will know if the Public Key stored on Keybase, is genuinely from the SeedSinger Project or not.

</p> </details> <br>

If the two ID's do not match, then you must stop here immediately. Do not continue. Contact us for assistance in the Telegram group address above.

<br>

Step 2. Verifying that the software images/binaries are genuine

Now that you have confirmed that you do have the real SeedSigner Project's Public Key (ie the 16 characters match) - you can return to your terminal window. Running the shasum command, is the final verification step and will confirm (via file hashing) that the software code/image files, were also not altered since publication, or even during your download process.
(Prior to version 0.6.0 , your verify command will check the .zip file which contains the binary files.)

On Linux or OSX: Run this command

shasum -a 256 --ignore-missing --check seedsigner.0.7.*.sha256.txt

On Windows (inside Powershell): Run this command

CertUtil -hashfile  seedsigner_os.0.7.0.Insert_Your_Pi_Models_binary_here_For_Example_pi02w.img SHA256

On Windows, you must then manually compare the resulting file hash value to the corresponding hash value shown inside the .SHA256 cleartext file. <BR>

Wait up to 30 seconds for the command to complete, and it should display:

seedsigner_os.0.7.x.[Your_Pi_Model_For_Example:pi02w].img: OK

If you receive the "OK" message for your seedsigner_os.0.7.x.[Your_Pi_Model_For_Example:pi02w].img file, as shown above, then your verification is fully complete!
All of your downloaded files have now been confirmed as both authentic and unaltered! You can proceed to create/write your MicroSD card😄😄 !!

If your file result shows "FAILED", then you must stop here immediately. Do not continue. Contact us for assistance at the Telegram group address above.

<BR>

Please recognize that this process can only validate the software to the extent that the entity that first published the key is an honest actor, and their private key is not compromised or somehow being used by a malicious actor. <BR> <BR>

Writing the software onto your MicroSD card

To write the SeedSigner software onto your MicroSD card, there are a few options available:

ApplicationDescriptionPlatform and official Source
Balena EtcherThe application is called Etcher, and the company that wrote it is called Balena. Hence Etcher by Balena or Balena EtcherAvailable for Windows, Mac and Linux
Raspberry Pi ImagerProduced by the Raspberry Pi organization.Available for Windows, Mac and Linux
DD Command Line UtilityBuilt-in to Linux and MacOS, the DD (Data Duplicator) is a tool for advanced users. If not used carefully it can accidentally format the incorrect disk!Built-in to Linux and MacOS

Be sure to download the software from the genuine publisher.
Either of the Etcher or Pi Imager software is recommended. Some SeedSigner users have reported a better experience with one or the other. So, if the one application doesn’t work well for your particular machine, then please try the other one. <BR>

General Considerations:

The writing and verify steps are very quick from version 0.6.0 upwards, so please pay close attention to your screen. Make sure to set any write-protection physical slider on the MicroSD Card Adapter to UN-locked.
You also don’t need to pre-format the MicroSD beforehand. You dont need to unzip any .zip file beforehand. Current Etcher and Pi Imager software will perform a verify action (by default) to make sure the card was written successfully! Watching for that verify step to complete successfully, can save you a lot of headaches if you later need to troubleshoot issues where your SeedSigner device doesn’t boot up at power on.
Writing the MicroSd card is also known as flashing.
It will overwrite everything on the MicroSD card.
If the one application fails for you, then please try again using our other recommended application.
Advanced users may want to try the Linux/MacOS DD command instead of using Etcher or Pi Imager, however, a reminder is given that DD can overwrite the wrong disk if you are not careful !

Specific considerations for Windows users:

Use the Pi imager software as your first choice on Windows. Windows can sometimes flag the writing of a MicroSD as risky behaviour and hence it may prevent this activity. If this happens, your writing/flashing will fail, hang or wont even begin, in which case you should to try to run the Etcher/Pi-Imager app "As administrator", (right-click and choose that option). It can also be blocked by windows security in some cases, so If you have the (non-default) Controlled Folder Access option set to active, try turning that off temporarily.

Enclosure Designs

Open Pill

The Open Pill enclosure design is all about quick, simple and inexpensive depoloyment of a SeedSigner device. The design does not require any additional hardware and can be printed using a standard FDM 3D printer in about 2 hours, no supports necessary. A video demonstrating the assembly process can be found here. To access the design file and printable model, click here.

Orange Pill

The Orange Pill enclosure design offers a more finished look that includes button covers and a joystick topper. You'll also need the following additional hardware to assemble it:

The upper and lower portions of the enclosure can be printed using a standard FDM 3D printer, no supports necessary. The buttons and joystick nub should ideally be produced with a SLA/resin printer. An overview of the entire assembly process can be found here. To access the design files and printable models, click here.

Community Designs

SeedQR Printable Templates

You can use SeedSigner to export your seed to a hand-transcribed SeedQR format that enables you to instantly load your seed back into SeedSigner.

More information about SeedQRs

<table align="center"> <tr><td><img src="docs/seed_qr/img/handmade_qr.jpg"></td></tr> </table>

Standard SeedQR templates:

CompactSeedQR templates:

2-sided SeedQR templates - 8 per sheet Printing settings - (2-sided)("flip on long edge")("Actual Size") If printing on cardstock, adjust your printer settings via its control panel

A4 templates(210mm * 297mm):

Letter templates(8.5in * 11in):

Build from Source

See the SeedSigner OS repo for instructions.

Developer Local Build Instructions

Raspberry Pi OS is commonly used for development. See the Raspberry Pi OS Build Instructions