Public/New-RSASignatureFromCertificate.ps1
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function New-RSASignatureFromCertificate { <# .SYNOPSIS Creates a new signature based on content using the private key of a certificate identified by its thumbprint. .DESCRIPTION Creates a new signature based on content using the private key of a certificate identified by its thumbprint. The certificate must be available in the LocalMachine\My certificate store and have a private key. .PARAMETER Content Specifies the content string to be signed. .PARAMETER Thumbprint Specifies the thumbprint of the certificate. .NOTES Author: Florian Salzmann Contact: @FlorianSLZ Created: 2024-06-21 Updated: 2024-06-21 Version history: 1.0.0 - (2024-06-21) Function created Credits to Nickolaj Andersen for the initial function. #> param( [parameter(Mandatory = $true, HelpMessage = "Specify the content string to be signed.")] [ValidateNotNullOrEmpty()] [string]$Content, [parameter(Mandatory = $true, HelpMessage = "Specify the thumbprint of the certificate.")] [ValidateNotNullOrEmpty()] [string]$Thumbprint ) Process { try { # Retrieve the certificate based on thumbprint $Certificate = Get-ChildItem -Path "Cert:\LocalMachine\My" -Recurse | Where-Object { $_.Thumbprint -eq $Thumbprint } if ($Certificate -ne $null -and $Certificate.HasPrivateKey) { # Get the RSA private key $RSAPrivateKey = [System.Security.Cryptography.X509Certificates.RSACertificateExtensions]::GetRSAPrivateKey($Certificate) if ($RSAPrivateKey -ne $null) { # Compute SHA256 hash of the content $SHA256Managed = [System.Security.Cryptography.SHA256Managed]::Create() $EncodedContentData = [System.Text.Encoding]::UTF8.GetBytes($Content) $ComputedHash = $SHA256Managed.ComputeHash($EncodedContentData) # Sign the hash with RSA private key $SignatureSigned = $RSAPrivateKey.SignHash($ComputedHash, [System.Security.Cryptography.HashAlgorithmName]::SHA256, [System.Security.Cryptography.RSASignaturePadding]::Pkcs1) # Convert signature to Base64 string $SignatureString = [System.Convert]::ToBase64String($SignatureSigned) return $SignatureString } else { Write-Error "Failed to retrieve RSA private key from the certificate." } } else { Write-Error "Certificate with thumbprint $Thumbprint not found or does not have a private key." } } catch { Write-Error "Error while creating RSA certificate signature: $_" } } } |