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Windows - Code signing guide locally & with GitHub Actions

Intro​

Code signing your application lets users know that they downloaded the official executable of your app and not some 3rd party malware that poses as your app. While it is not required, it improves users' confidence in your app.

Prerequisites​

  • Windows - you can likely use other platforms, but this tutorial uses Powershell native features.
  • A working Tauri application
  • Code signing certificate - you can acquire one of these on services listed in Microsoft's docs. There are likely additional authorities for non-EV certificates than included in that list, please compare them yourself and choose one at your own risk.
    • Please make sure to get a code signing certificate, SSL certificates do not work!

This guide assumes that you have a standard code signing certificate> If you have an EV certificate, which generally involves a hardware token, please follow your issuer's documentation instead.

note

If you sign the app with an EV Certificate, it'll receive an immediate reputation with Microsoft SmartScreen and won't show any warnings to users.

If you opt for an OV Certificate, which is generally cheaper and available to individuals, Microsoft SmartScreen will still show a warning to users when they download the app. It might take some time until your certificate builds enough reputation. You may opt for submitting your app to Microsoft for manual review. Although not guaranteed, if the app does not contain any malicious code, Microsoft may grant additional reputation and potentially remove the warning for that specific uploaded file.

Getting Started​

There are a few things we have to do to get Windows prepared for code signing. This includes converting our certificate to a specific format, installing this certificate, and decoding the required information from the certificate.

A. Convert your .cer to .pfx​

  1. You will need the following:

    • certificate file (mine is cert.cer)
    • private key file (mine is private-key.key)

  2. Open up a command prompt and change to your current directory using cd Documents/Certs

  3. Convert your .cer to a .pfx using openssl pkcs12 -export -in cert.cer -inkey private-key.key -out certificate.pfx

  4. You should be prompted to enter an export password DON'T FORGET IT!

B. Import your .pfx file into the keystore.​

We now need to import our .pfx file.

  1. Assign your export password to a variable using $WINDOWS_PFX_PASSWORD = 'MYPASSWORD'

  2. Now Import the certificate using Import-PfxCertificate -FilePath Certs/certificate.pfx -CertStoreLocation Cert:\CurrentUser\My -Password (ConvertTo-SecureString -String $env:WINDOWS_PFX_PASSWORD -Force -AsPlainText)

C. Prepare Variables​

  1. We need the SHA-1 thumbprint of the certificate; you can get this using openssl pkcs12 -info -in certificate.pfx and look under for following
Bag Attributes
    localKeyID: A1 B1 A2 B2 A3 B3 A4 B4 A5 B5 A6 B6 A7 B7 A8 B8 A9 B9 A0 B0

  1. You will capture the localKeyID but with no spaces, in this example, it would be A1B1A2B2A3B3A4B4A5B5A6B6A7B7A8B8A9B9A0B0. This is our certificateThumbprint.

  2. We need the SHA digest algorithm used for your certificate (Hint: this is likely sha256

  3. We also need a timestamp URL; this is a time server used to verify the time of the certificate signing. I'm using http://timestamp.comodoca.com, but whoever you got your certificate from likely has one as well.

Prepare tauri.conf.json file​

  1. Now that we have our certificateThumbprint, digestAlgorithm, & timestampUrl we will open up the tauri.conf.json.

  2. In the tauri.conf.json you will look for the tauri -> bundle -> windows section. You see, there are three variables for the information we have captured. Fill it out like below.

"windows": {
        "certificateThumbprint": "A1B1A2B2A3B3A4B4A5B5A6B6A7B7A8B8A9B9A0B0",
        "digestAlgorithm": "sha256",
        "timestampUrl": "http://timestamp.comodoca.com"
}

  1. Save and run yarn | yarn build

  2. In the console output, you should see the following output.

info: signing app
info: running signtool "C:\\Program Files (x86)\\Windows Kits\\10\\bin\\10.0.19041.0\\x64\\signtool.exe"
info: "Done Adding Additional Store\r\nSuccessfully signed: APPLICATION FILE PATH HERE

Which shows you have successfully signed the .exe.

And that's it! You have successfully signed your .exe file.

BONUS: Sign your application with GitHub Actions.​

We can also create a workflow to sign the application with GitHub actions.

GitHub Secrets​

We need to add a few GitHub secrets for the proper configuration of the GitHub Action. These can be named however you would like.

The secrets we used are as follows

GitHub SecretsValue for Variable
WINDOWS_CERTIFICATEBase64 encoded version of your .pfx certificate, can be done using this command certutil -encode certificate.pfx base64cert.txt
WINDOWS_CERTIFICATE_PASSWORDCertificate export password used on creation of certificate .pfx

Workflow Modifications​

  1. We need to add a step in the workflow to import the certificate into the Windows environment. This workflow accomplishes the following

    1. Assign GitHub secrets to environment variables
    2. Create a new certificate directory
    3. Import WINDOWS_CERTIFICATE into tempCert.txt
    4. Use certutil to decode the tempCert.txt from base64 into a .pfx file.
    5. Remove tempCert.txt
    6. Import the .pfx file into the Cert store of Windows & convert the WINDOWS_CERTIFICATE_PASSWORD to a secure string to be used in the import command.

  2. We will be using the tauri-action publish template.

name: 'publish'
on:
  push:
    branches:
      - release

jobs:
  publish-tauri:
    strategy:
      fail-fast: false
      matrix:
        platform: [macos-latest, ubuntu-latest, windows-latest]

    runs-on: ${{ matrix.platform }}
    steps:
      - uses: actions/checkout@v2
      - name: setup node
        uses: actions/setup-node@v1
        with:
          node-version: 12
      - name: install Rust stable
        uses: actions-rs/toolchain@v1
        with:
          toolchain: stable
      - name: install webkit2gtk (ubuntu only)
        if: matrix.platform == 'ubuntu-latest'
        run: |
          sudo apt-get update
          sudo apt-get install -y webkit2gtk-4.0
      - name: install app dependencies and build it
        run: yarn && yarn build
      - uses: tauri-apps/tauri-action@v0
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        with:
          tagName: app-v__VERSION__ # the action automatically replaces \_\_VERSION\_\_ with the app version
          releaseName: 'App v__VERSION__'
          releaseBody: 'See the assets to download this version and install.'
          releaseDraft: true
          prerelease: false
  1. Right above -name: install app dependencies and build it you will want to add the following step
- name: import windows certificate
  if: matrix.platform == 'windows-latest'
  env:
    WINDOWS_CERTIFICATE: ${{ secrets.WINDOWS_CERTIFICATE }}
    WINDOWS_CERTIFICATE_PASSWORD: ${{ secrets.WINDOWS_CERTIFICATE_PASSWORD }}
  run: |
    New-Item -ItemType directory -Path certificate
    Set-Content -Path certificate/tempCert.txt -Value $env:WINDOWS_CERTIFICATE
    certutil -decode certificate/tempCert.txt certificate/certificate.pfx
    Remove-Item -path certificate -include tempCert.txt
    Import-PfxCertificate -FilePath certificate/certificate.pfx -CertStoreLocation Cert:\CurrentUser\My -Password (ConvertTo-SecureString -String $env:WINDOWS_CERTIFICATE_PASSWORD -Force -AsPlainText)

  1. Save and push to your repo.

  2. Your workflow can now import your windows certificate and import it into the GitHub runner, allowing for automated code signing!