Code signing in PowerShell - Step-by-Step Execution

Concept Flow - Code signing

Write Script File

↓

Generate Signing Certificate

↓

Sign Script with Certificate

↓

Verify Signature

↓

Run Script

↓

Execution Allowed if Signature Valid

↓

END

This flow shows how a script is created, signed with a certificate, verified, and then allowed to run if the signature is valid.

Execution Sample

PowerShell

Set-AuthenticodeSignature -FilePath .\MyScript.ps1 -Certificate $cert
Get-AuthenticodeSignature -FilePath .\MyScript.ps1

This code signs a PowerShell script file with a certificate and then checks the signature status.

Execution Table

Step	Action	Input/Condition	Result	Output
1	Sign Script	File: MyScript.ps1, Certificate: $cert	Signature added to script	Signature.Status = Valid
2	Verify Signature	File: MyScript.ps1	Check signature validity	Signature.Status = Valid
3	Run Script	Signature.Status == Valid	Script runs successfully	Script output or actions executed
4	Run Script	Signature.Status != Valid	Script blocked or warning shown	No script execution

💡 Execution stops if signature is invalid or missing, preventing script run.

Variable Tracker

Variable	Start	After Signing	After Verification	After Run
$cert	Certificate object loaded	Certificate object loaded	Certificate object loaded	Certificate object loaded
Signature.Status	None	Valid	Valid	Valid or Invalid depending on verification
Script Execution	Not started	Not started	Ready to run	Executed or blocked

Key Moments - 3 Insights

Why does the script not run if the signature is invalid?

Because the verification step (see execution_table step 4) checks the signature status and blocks execution if it is not valid to protect from untrusted code.

What happens if you sign the script with a wrong or expired certificate?

The signature status will be invalid during verification (execution_table step 2), causing the script to be blocked at run time.

Is the certificate variable ($cert) changed after signing?

No, $cert remains the same certificate object throughout (see variable_tracker), it is used to sign but not modified.

Visual Quiz - 3 Questions

Look at the execution_table, what is the signature status immediately after signing the script?

A Valid

B Invalid

C None

D Expired

💡 Hint

Check execution_table row 1, Output column shows Signature.Status after signing.

At which step does the script get blocked if the signature is invalid?

A Step 1 - Signing

B Step 4 - Running with invalid signature

C Step 3 - Running

D Step 2 - Verification

💡 Hint

Look at execution_table row 4 where script is blocked due to invalid signature.

If the certificate variable $cert was null, what would happen during signing?

A Script signs successfully

B Signature status becomes Valid anyway

C Signing fails, no signature added

D Script runs without signature

💡 Hint

Refer to variable_tracker and execution_table step 1 where certificate is required for signing.

Concept Snapshot

Code signing in PowerShell:
- Use Set-AuthenticodeSignature with a certificate to sign scripts.
- Use Get-AuthenticodeSignature to verify signature status.
- Script runs only if signature is valid.
- Protects from running untrusted or altered scripts.
- Certificate must be valid and trusted.

Full Transcript

Code signing in PowerShell involves creating a script file, then using a certificate to sign it with the Set-AuthenticodeSignature command. This adds a digital signature to the script. Later, the signature is checked using Get-AuthenticodeSignature to confirm it is valid. If the signature is valid, the script is allowed to run safely. If invalid or missing, the script is blocked to protect the system from untrusted code. The certificate used for signing remains unchanged during this process. This ensures scripts are trusted and have not been tampered with before execution.