Decrypt a govtalk.gov.uk SOAP GovTalkMessage

Demonstrates how to decrypt the content contained in the XML of a GovTalkMessage SOAP response.
Chilkat C# Downloads

bool success = false;

// 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...

Chilkat.Xml xml = new Chilkat.Xml();
success = xml.LoadXmlFile("qa_data/xml/govTalkMessageResponse.xml");
if (success == false) {
    Debug.WriteLine(xml.LastErrorText);
    return;
}

string Body = xml.GetChildContent("Body|Message|Body");
Debug.WriteLine(Body);

Chilkat.Cert cert = new Chilkat.Cert();
success = cert.LoadPfxFile("qa_data/pfx/govTalkMessage_aaa.pfx","aaa");
if (success == false) {
    Debug.WriteLine(cert.LastErrorText);
    return;
}

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();
crypt.CryptAlgorithm = "pki";
success = crypt.SetDecryptCert(cert);
if (success == false) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

Chilkat.BinData bd = new Chilkat.BinData();
// Append the bytes to bd.
success = bd.AppendEncoded(Body,"base64");

// Decrypt in-place.
success = crypt.DecryptBd(bd);
if (success == false) {
    Debug.WriteLine(crypt.LastErrorText);
    return;
}

// 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:
Debug.WriteLine("Decrypted bytes as hex: " + bd.GetEncoded("hex"));