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://learn.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"

Answer 2

Based on what PowerShellGuy mentioned.

Will that work for you?

# first get your cert, either via pure .NET, or through the PSDrive (Cert:\)

# this is just an example

# get cert from PSDrive
$cert = Get-ChildItem Cert:\LocalMachine\My | where Subject -eq 'CN=MySubject'

# get cert from .NET
$My     = [System.Security.Cryptography.X509Certificates.StoreName]::My
$Store  = [System.Security.Cryptography.X509Certificates.X509Store]::new($My,'localmachine')
$Store.Open([System.Security.Cryptography.X509Certificates.OpenFlags]::MaxAllowed)

$cert   = $Store.Certificates | where Subject -eq 'CN=MySubject'

# get private key
# PKCS8, way #1
$BytesPkcs8 = $cert.PrivateKey.ExportPkcs8PrivateKey()
[System.Convert]::ToBase64String($BytesPkcs8)

# PKCS8, way #2
$Pkcs = [System.Security.Cryptography.CngKeyBlobFormat]::Pkcs8PrivateBlob
$BytesPkcs8 = $cert.PrivateKey.Key.Export($Pkcs)
[System.Convert]::ToBase64String($BytesPkcs8)

# RSA
$BytesRsa = $cert.PrivateKey.ExportRSAPrivateKey()
[System.Convert]::ToBase64String($BytesRsa)

So is that Base64 string what you're looking for?

Answer 3

Try this script which exports the private key in Pkcs8 format

Azure PowerShell - Extract PEM from SSL certificate