Create a self-signed certificate with PowerShell

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Tim Buntrock

Tim Buntrock is one of three enterprise administrators for the Active Directory service of a "global player" in the contact center business. He is a certified engineer for MCTS, MCITP, MCSA and MCPS.

Latest posts by Tim Buntrock (see all)

• Create a self-signed certificate with PowerShell - Thu, Aug 9 2018
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A self-signed certificate is a certificate you sign with your own private key. In contrast, an external public internet certificate authority (CA) signs a public certificate. You can also have your own private CA in which you can issue a private certificate.

Here, we are only concerned about self-signed certificates and creating them with PowerShell. Note that you need at least PowerShell 4 to follow the instructions in this article.

The command below uses the cmdlet New-SelfSignedCertificate to create a certificate and store it in the certificate store of the local machine.

New-SelfSignedCertificate -certstorelocation cert:\localmachine\my -dnsname wifi.domain.com

In this example, I use the fully qualified domain name (FQDN) "wifi.domain.com." You can use the internet domain of your organization.

Creating a self signed certificate with New SelfSignedCertificate

Copy the thumbprint to use later on. This is the thumbprint in the example above: AA99819711BB1A0572F15C2C3369DE078A1FCBE3

Next, we store a password into the variable $pw:

$pw = ConvertTo-SecureString -String "Pazzword" -Force -AsPlainText

The following command uses the Export-PfxCertificate cmdlet and the thumbprint from above to export the certificate to a file.

Export-PfxCertificate -cert cert:\localMachine\my\AA99819711BB1A0572F15C2C3369DE078A1FCBE3 -FilePath $env:USERPROFILE\Desktop\Cert.pfx -Password $pw

If you have to follow the procedure often, you can use this little script:

$Certname = Read-Host "Enter Certificate Name"
$Cert = New-SelfSignedCertificate -certstorelocation cert:\localmachine\my -dnsname $Certname
$pw = ConvertTo-SecureString -String "Pazzword" -Force -AsPlainText
$thumbprint = $Cert.Thumbprint

The script uses the Read-Host cmdlet to prompt the user for the certificate name. It then stores the certificate, password, and thumbprint in variables it then uses to export the certificate to a file.

Create a certificate with a PowerShell script

After the script runs, you should see the certificate on your desktop and in the certificate store.

Certificate file on the desktop

The certificate in the Certificates snap in

By default, the certificate will expire in one year. If you want to specify the certificate expiration, you just have to use the -NotAfter parameter with the New-SelfSignedCertificate cmdlet:

$YearsToExpire = Read-Host “How many years should this certificate be valid”
$Cert = New-SelfSignedCertificate -certstorelocation cert:\localmachine\my -dnsname $Certname -NotAfter (Get-Date).AddYears($YearsToExpire)

This is the entire script:

# Create and export a self-signed certificate
# Script by Tim Buntrock

# Define certificate name
$Certname = Read-Host “Enter Certificate Name”
# Define expiration
$YearsToExpire = Read-Host “How many years should this certificate be valid”
Write-Host "Creating Certifcate $Certname" -ForegroundColor Green
# Create certificate
$Cert = New-SelfSignedCertificate -certstorelocation cert:\localmachine\my -dnsname $Certname -NotAfter (Get-Date).AddYears($YearsToExpire)
Write-Host "Exporting Certificate $Certname to $env:USERPROFILE\Desktop\$Certname.pfx" -ForegroundColor Green
# Set password to export certificate
$pw = ConvertTo-SecureString -String "Pazzword" -Force -AsPlainText
# Get thumbprint
$thumbprint = $Cert.Thumbprint
# Export certificate
Export-PfxCertificate -cert cert:\localMachine\my\$thumbprint -FilePath $env:USERPROFILE\Desktop\$Certname.pfx -Password $pw