Extract private key from pfx file or certificate store WITHOUT using OpenSSL on Windows

Question

As the title suggests I would like to export my private key without using OpenSSL or any other third party tool. If I need a .cer file or .pfx file I can easily export these via MMC or PowerShell pkiclient but I can't find a way to get the private key.

https://docs.microsoft.com/en-us/powershell/module/pkiclient/export-certificate?view=win10-ps

Using an online tool like https://www.sslshopper.com/ssl-converter.html is not OK.

PSVersion:

PS C:\Users\oscar> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      5.1.17134.228
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.17134.228
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

I can get the public key like this:

(Get-PfxCertificate -FilePath C:\Users\oscar\Desktop\localhost.pfx).GetPublicKey()

And export the entire certificate like this:

(Get-PfxCertificate -FilePath C:\Users\oscar\Desktop\localhost.pfx).GetRawCertData()

Result from

PS C:\Users\oscar> $mypwd = ConvertTo-SecureString -String "MyPassword" -Force -AsPlainText
PS C:\Users\oscar> $mypfx = Get-PfxData -FilePath C:\Users\oscar\Desktop\localhost.pfx -Password $mypwd
PS C:\Users\oscar> $mypfx

OtherCertificates EndEntityCertificates
----------------- ---------------------
{}                {[Subject]...


PS C:\Users\oscar> $mypfx.EndEntityCertificates

Thumbprint                                Subject
----------                                -------
8ED4971564E35099D6DB490C3756E2AD43AAAAAA  CN=localhost

Tested the command from @Brad but I got the error below.

Private key is NOT plain text exportable

certutil -exportPFX -p "myPassword" -privatekey -user my <Certificate Serial Number> C:\localhost.pfx

Similar to Certificate Export Wizard in MMC certificates, only export to .pfx available if the key is included.

Answer 1

I had the same problem and solved it with the help of PSPKI Powershell module from PS Gallery. While I understand that you look for a solution that preferably uses some built in functionality in Windows, installing a module from PS Gallery might be acceptable. At least it was in my case.

First install the PSPKI module (I assume hat the PSGallery repository has already been set up):

Install-Module -Name PSPKI

The PSPKI module provides a Cmdlet Convert-PfxToPem which converts a pfx-file to a pem-file which contains the certificate and pirvate key as base64-encoded text:

Convert-PfxToPem -InputFile C:\path\to\pfx\file.pfx -Outputfile C:\path\to\pem\file.pem

Now, all we need to do is splitting the pem-file with some regex magic. For example, like this:

(Get-Content C:\path\to\pem\file.pem -Raw) -match "(?ms)(\s*((?<privatekey>-----BEGIN PRIVATE KEY-----.*?-
----END PRIVATE KEY-----)|(?<certificate>-----BEGIN CERTIFICATE-----.*?-----END CERTIFICATE-----))\s*){2}"

$Matches["privatekey"] | Set-Content "C:\path\to\key\file.pem"
$Matches["certificate"] | Set-Content "C:\path\to\certificate\file.pem"