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"));