(PowerShell) Decrypt a govtalk.gov.uk SOAP GovTalkMessage

Demonstrates how to decrypt the content contained in the XML of a GovTalkMessage SOAP response.

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Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# This example assumes the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

# The GovTalkMessage response looks something like this:

# <?xml version="1.0" encoding="utf-8"?>
# <GovTalkMessage xmlns="http://www.govtalk.gov.uk/CM/envelope">
#   <EnvelopeVersion>3.1</EnvelopeVersion>
#   <Header>
#     <MessageDetails>
#       <Class>CSSZ_DZDPN</Class>
#       <Qualifier>request</Qualifier>
#       <Function>submit</Function>
#       <TransactionID />
#       <AuditID />
#       <CorrelationID>aaaaa</CorrelationID>
#       <ResponseEndPoint PollInterval="0" />
#       <Transformation>XML</Transformation>
#       <GatewayTest />
#       <GatewayTimestamp />
#     </MessageDetails>
#     <SenderDetails>
#       <IDAuthentication>
#         <SenderID />
#         <Authentication>
#           <Method>clear</Method>
#           <Role />
#           <Value />
#         </Authentication>
#       </IDAuthentication>
#       <X509Certificate />
#       <EmailAddress>somebody@example.com</EmailAddress>
#     </SenderDetails>
#   </Header>
#   <GovTalkDetails>
#     <Keys>
#       <Key Type="vars">9999999999</Key>
#     </Keys>
#     <GatewayAdditions>
#       <Source>VREP</Source>
#     </GatewayAdditions>
#   </GovTalkDetails>
#   <Body>
#     <Message xmlns="http://www.cssz.cz/XMLSchema/envelope" version="1.2" eType="DZDPN20">
#       <Header>
#         <Signature xmlns:dt="urn:schemas-microsoft-com:datatypes" dt:dt="bin.base64">MIIJ0A ... UMw=
# </Signature>
#         <Vendor productName="some product name" version="2019" />
#       </Header>
#       <Body xmlns:dt="urn:schemas-microsoft-com:datatypes" encrypted="yes" contentEncoding="gzip" dt:dt="bin.base64">MIIF2w ... N2vW</Body>
#     </Message>
#   </Body>
# </GovTalkMessage>

# We want to get the content of the Body and decrypt it.

# First, let's get the content of the Body XML element, which is a base64 string starting with MIIF2w...

$xml = New-Object Chilkat.Xml
$success = $xml.LoadXmlFile("qa_data/xml/govTalkMessageResponse.xml")
if ($success -eq $false) {
    $($xml.LastErrorText)
    exit
}

$Body = $xml.GetChildContent("Body|Message|Body")
$($Body)

$cert = New-Object Chilkat.Cert
$success = $cert.LoadPfxFile("qa_data/pfx/govTalkMessage_aaa.pfx","aaa")
if ($success -eq $false) {
    $($cert.LastErrorText)
    exit
}

$crypt = New-Object Chilkat.Crypt2
$crypt.CryptAlgorithm = "pki"
$success = $crypt.SetDecryptCert($cert)
if ($success -eq $false) {
    $($crypt.LastErrorText)
    exit
}

$bd = New-Object Chilkat.BinData
# Append the bytes to bd.
$success = $bd.AppendEncoded($Body,"base64")

# Decrypt in-place.
$success = $crypt.DecryptBd($bd)
if ($success -eq $false) {
    $($crypt.LastErrorText)
    exit
}

# Save the decrypted data to a file.
$success = $bd.WriteFile("qa_output/out.dat")

# If the decrypted data is non-text (binary) then we can examine it in an encoding, such as hex:
$("Decrypted bytes as hex: " + $bd.GetEncoded("hex"))