Generate Self-signed certificate with Root CA Signer

Question

Scenario: I am using PowerShell on Windows Server 2012r2 to generate a Root certificate and want to use that to sign a newly created Intermediate and Web certificate in dynamic generated (and destroyed) dev/test environments. The scripts are deployed remotely, and the intent is to keep it pure PowerShell if possible. In Windows 10/2016 this is relatively easy, after generating the Root certificate:

$Cert = New-SelfSignedCertificate -Signer $Root -Subject "CN=$Subject"

I've generated the Root certificate using COM X509Enrollment.CX509CertificateRequestCertificate and Security.Cryptography.X509Certificates.X509Certificate2 in a bastardized PS that I've had for some time, mainly because I needed to ensure that the Subject and Usage were set very specifically. I am not quite certain how to use this to sign the standard certificate without the above (which I have used before).

There are some examples using Bouncy Castle (see below) in C# that I could tie into PowerShell, but then I would need to deploy this additionally on the dynamic dev/test environments and I want to be able to do this in Powershell (via COM if needed) with the least dependencies.

• C# Generate Self Signed Certificates on the Fly
• How do I use Bouncy Castle in Powershell

Answer 1

The ultimate solution in my case, avoiding makecert and openssl was to use Powershell and BouncyCastle. I forked the PSBouncyCastle repo from PSBouncyCastle by RLipscombe and pushed 1.8.1 Bouncy Castle in. My forked version is the one I've used for the script, the fork resides at Forked: PSBouncyCastle.New.

I then used StackOverflow: C# Generate Certificates on the Fly as inspiration to write the following powershell below, I will be adding this to my GitHub and commenting, and I will amend this as soon as I do:

Import-Module -Name PSBouncyCastle.New

function New-SelfSignedCertificate {
  [CmdletBinding()]
  param (
    [string]$SubjectName,
    [string]$FriendlyName = "New Certificate",
    [object]$Issuer,
    [bool]$IsCA = $false,
    [int]$KeyStrength = 2048,
    [int]$ValidYears = 2,
    [hashtable]$EKU = @{}
  )

  # Needed generators
  $random = New-SecureRandom
  $certificateGenerator = New-CertificateGenerator

  if($Issuer -ne $null -and $Issuer.HasPrivateKey -eq $true)
  {
    $IssuerName = $Issuer.IssuerName.Name
    $IssuerPrivateKey = $Issuer.PrivateKey
  }
  # Create and set a random certificate serial number
  $serial = New-SerialNumber -Random $random
  $certificateGenerator.SetSerialNumber($serial)

  # The signature algorithm
  $certificateGenerator.SetSignatureAlgorithm('SHA256WithRSA')

  # Basic Constraints - certificate is allowed to be used as intermediate.
  # Powershell requires either a $null or reassignment or it will return this from the function
  $certificateGenerator = Add-BasicConstraints -isCertificateAuthority $IsCA -certificateGenerator $certificateGenerator

  # Key Usage
  if($EKU.Count -gt 0) 
  {
    $certificateGenerator = $certificateGenerator | Add-ExtendedKeyUsage @EKU
  }
  # Create and set the Issuer and Subject name
  $subjectDN = New-X509Name -Name ($SubjectName)
  if($Issuer -ne $null) {
    $IssuerDN = New-X509Name -Name ($IssuerName)
  }
  else 
  {
    $IssuerDN = New-X509Name -Name ($SubjectName)
  }  
  $certificateGenerator.SetSubjectDN($subjectDN)
  $certificateGenerator.SetIssuerDN($IssuerDN)

  # Authority Key and Subject Identifier
  if($Issuer -ne $null)
  {
    $IssuerKeyPair = ConvertTo-BouncyCastleKeyPair -PrivateKey $IssuerPrivateKey
    $IssuerSerial = [Org.BouncyCastle.Math.BigInteger]$Issuer.GetSerialNumber()
    $authorityKeyIdentifier = New-AuthorityKeyIdentifier -name $Issuer.IssuerName.Name -publicKey $IssuerKeyPair.Public -serialNumber $IssuerSerial
    $certificateGenerator = Add-AuthorityKeyIdentifier -certificateGenerator $certificateGenerator -authorityKeyIdentifier $authorityKeyIdentifier
  }

  # Validity range of the certificate
  [DateTime]$notBefore = (Get-Date).AddDays(-1)
  if($ValidYears -gt 0) {
    [DateTime]$notAfter = $notBefore.AddYears($ValidYears)
  }
  $certificateGenerator.SetNotBefore($notBefore)
  $certificateGenerator.SetNotAfter($notAfter)


  # Subject public key ~and private
  $subjectKeyPair = New-KeyPair -Strength $keyStrength -Random $random
  if($IssuerPrivateKey -ne $null)
  {
    $IssuerKeyPair = [Org.BouncyCastle.Security.DotNetUtilities]::GetKeyPair($IssuerPrivateKey)
  }
  else 
  {
    $IssuerKeyPair = $subjectKeyPair
  }
  $certificateGenerator.SetPublicKey($subjectKeyPair.Public)

  # Create the Certificate
  $IssuerKeyPair = $subjectKeyPair
  $certificate = $certificateGenerator.Generate($IssuerKeyPair.Private, $random)
  # At this point you have the certificate and need to convert it and export, I return the private key for signing the next cert
  $pfxCertificate = ConvertFrom-BouncyCastleCertificate -certificate $certificate -subjectKeyPair $subjectKeyPair -friendlyName $FriendlyName
  return $pfxCertificate
}

A few examples of usage for this powershell would be:

Generate a Root CA

$TestRootCA = New-SelfSignedCertificate -subjectName "CN=TestRootCA" -IsCA $true
Export-Certificate -Certificate $test -OutputFile "TestRootCA.pfx" -X509ContentType Pfx

Generate a Standard Self Signed

$TestSS = New-SelfSignedCertificate -subjectName "CN=TestLocal"
Export-Certificate -Certificate $TestSS -OutputFile "TestLocal.pfx" -X509ContentType Pfx

Generate a certificate, signing with a root certificate

$TestRootCA = New-SelfSignedCertificate -subjectName "CN=TestRootCA" -IsCA $true
$TestSigned = New-SelfSignedCertificate -subjectName "CN=TestSignedByRoot" -issuer $TestRootCA

Export-Certificate -Certificate $test -OutputFile "TestRootCA.pfx" -X509ContentType Pfx
Export-Certificate -Certificate $test -OutputFile "TestRootCA.pfx" -X509ContentType Pfx

Generate a Self-Signed with Specific Usage

$TestServerCert = New-SelfSignedCertificate -subjectName "CN=TestServerCert" -EKU @{ "ServerAuthentication" = $true }

Note that the -EKU parameter accepts via splatting, it does this to ensure that anything added to Add-ExtendedKeyUsage is validly passed. It accepts the following certificate usages:

• DigitalSignature
• NonRepudiation
• KeyEncipherment
• DataEncipherment
• KeyAgreement
• KeyCertSign
• CrlSign
• EncipherOnly
• DecipherOnly

This fits my need and seems to work across all Windows Platforms we are using for dynamic environments.