Code signing in PowerShell

Introduction

Code signing helps prove that a script or program is safe and comes from a trusted source. It stops others from changing your code without permission.

When you want to share a PowerShell script with others and ensure it is not changed.

When running scripts on a system that requires signed scripts for security.

When distributing software to customers who need to trust your code.

When automating tasks in a company that enforces script signing policies.

Syntax

PowerShell

Set-AuthenticodeSignature -FilePath <path-to-script> -Certificate <certificate-object>

You need a code signing certificate to sign scripts.

The can be obtained from your certificate store or a file.

Examples

This signs the script located at C:\Scripts\MyScript.ps1 using the certificate stored in the variable $cert.

PowerShell

Set-AuthenticodeSignature -FilePath "C:\Scripts\MyScript.ps1" -Certificate $cert

This finds a certificate with 'MyCodeSigningCert' in its subject and uses it to sign the script.

PowerShell

$cert = Get-ChildItem -Path Cert:\CurrentUser\My | Where-Object { $_.Subject -like "*MyCodeSigningCert*" } | Select-Object -First 1
Set-AuthenticodeSignature -FilePath "C:\Scripts\MyScript.ps1" -Certificate $cert

Sample Program

This script looks for a code signing certificate in the current user's certificate store. If it finds one, it signs the script at C:\Scripts\ExampleScript.ps1 and prints a success message. If not, it tells you no certificate was found.

PowerShell

$cert = Get-ChildItem -Path Cert:\CurrentUser\My | Where-Object { $_.Subject -like "*Code Signing*" } | Select-Object -First 1
if ($cert) {
    Set-AuthenticodeSignature -FilePath "C:\Scripts\ExampleScript.ps1" -Certificate $cert
    Write-Output "Script signed successfully."
} else {
    Write-Output "No suitable code signing certificate found."
}

Important Notes

You must have a valid code signing certificate installed on your computer.

Unsigned scripts may be blocked from running depending on your system's execution policy.

Always keep your private key secure to prevent misuse.

Summary

Code signing proves your script is from you and has not been changed.

Use Set-AuthenticodeSignature with a certificate to sign scripts.

Signed scripts help keep your system safe and trusted.

Practice

1. What is the main purpose of code signing a PowerShell script?

easy

A. To prove the script is from a trusted source and has not been altered

B. To make the script run faster

C. To encrypt the script content

D. To convert the script into an executable file

Solution

1. Step 1: Understand code signing purpose

   Code signing is used to verify the identity of the script author and ensure the script has not been changed.

2. Step 2: Compare options

   Only To prove the script is from a trusted source and has not been altered describes this purpose correctly. Other options describe unrelated actions like encryption or performance.

3. Final Answer:

   To prove the script is from a trusted source and has not been altered -> Option A

4. Quick Check:

   Code signing = prove trust and integrity [OK]

Hint: Code signing proves trust and no changes [OK]

Common Mistakes:

• Thinking code signing encrypts the script
• Believing code signing speeds up execution
• Confusing code signing with file conversion

2. Which PowerShell command is used to sign a script with a certificate?

easy

A. New-ScriptSignature

B. Sign-ScriptCertificate

C. Set-AuthenticodeSignature

D. Add-ScriptCertificate

Solution

1. Step 1: Identify the correct cmdlet for signing

   The official PowerShell cmdlet to sign scripts is Set-AuthenticodeSignature.

2. Step 2: Verify other options

   Other options are not valid PowerShell commands for signing scripts.

3. Final Answer:

   Set-AuthenticodeSignature -> Option C

4. Quick Check:

   Sign script cmdlet = Set-AuthenticodeSignature [OK]

Hint: Remember: Set-AuthenticodeSignature signs scripts [OK]

Common Mistakes:

• Using non-existent cmdlets like Sign-ScriptCertificate
• Confusing signing with creating certificates
• Misspelling the cmdlet name

3. What will be the output of this PowerShell command if the script is successfully signed?

Set-AuthenticodeSignature -FilePath 'script.ps1' -Certificate $cert

medium

A. The script file is deleted

B. An error message about missing parameters

C. No output is shown

D. A Signature object showing Status as Valid

Solution

1. Step 1: Understand Set-AuthenticodeSignature output

   This cmdlet returns a Signature object with a Status property indicating if signing succeeded.

2. Step 2: Interpret successful signing output

   If signing succeeds, Status will be 'Valid'. No deletion or silent output occurs.

3. Final Answer:

   A Signature object showing Status as Valid -> Option D

4. Quick Check:

   Successful signing = Status Valid output [OK]

Hint: Successful signing returns Status Valid object [OK]

Common Mistakes:

• Expecting no output after signing
• Thinking the script file is deleted
• Confusing error messages with success

4. You run this command but get an error: Set-AuthenticodeSignature : Cannot find the certificate. What is the likely cause?

medium

A. The script is already signed

B. The certificate variable is empty or invalid

C. PowerShell version is too old

D. The script file path is incorrect

Solution

1. Step 1: Analyze the error message

   The error says it cannot find the certificate, meaning the $cert variable is likely empty or invalid.

2. Step 2: Check other options

   Incorrect file path causes a different error. PowerShell version or existing signature do not cause this specific error.

3. Final Answer:

   The certificate variable is empty or invalid -> Option B

4. Quick Check:

   Certificate missing error = invalid $cert [OK]

Hint: Check certificate variable if 'Cannot find certificate' error [OK]

Common Mistakes:

• Assuming file path is the problem
• Thinking PowerShell version causes this error
• Believing script already signed causes this error

5. You want to sign multiple scripts in a folder using the same certificate. Which PowerShell snippet correctly signs all .ps1 files?

hard

A. Get-ChildItem -Path . -Filter '*.ps1' | ForEach-Object { Set-AuthenticodeSignature -FilePath $_.FullName -Certificate $cert }

B. Set-AuthenticodeSignature -FilePath '*.ps1' -Certificate $cert

C. ForEach ($file in '*.ps1') { Set-AuthenticodeSignature -FilePath $file -Certificate $cert }

D. Get-Content '*.ps1' | Set-AuthenticodeSignature -Certificate $cert

Solution

1. Step 1: Identify correct way to get all .ps1 files

   Get-ChildItem -Filter '*.ps1' lists all script files in the folder.

2. Step 2: Apply signing to each file

   Using ForEach-Object to call Set-AuthenticodeSignature on each file with the certificate is correct.

3. Step 3: Check other options

   Set-AuthenticodeSignature -FilePath '*.ps1' -Certificate $cert tries to sign a wildcard path directly (invalid). ForEach ($file in '*.ps1') { Set-AuthenticodeSignature -FilePath $file -Certificate $cert } treats '*.ps1' as a string list (wrong). Get-Content '*.ps1' | Set-AuthenticodeSignature -Certificate $cert pipes file content, not file paths (wrong).

4. Final Answer:

   Get-ChildItem -Path . -Filter '*.ps1' | ForEach-Object { Set-AuthenticodeSignature -FilePath $_.FullName -Certificate $cert } -> Option A

5. Quick Check:

   Use Get-ChildItem + ForEach-Object to sign all scripts [OK]

Hint: Use Get-ChildItem and ForEach-Object to sign multiple files [OK]

Common Mistakes:

• Trying to sign wildcard paths directly
• Using file content instead of file paths
• Treating '*.ps1' as a list of files