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

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

Chilkat Tcl Extension Downloads

Chilkat Tcl Extension Downloads

load ./chilkat.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...

set xml [new_CkXml]

set success [CkXml_LoadXmlFile $xml "qa_data/xml/govTalkMessageResponse.xml"]
if {$success == 0} then {
    puts [CkXml_lastErrorText $xml]
    delete_CkXml $xml
    exit
}

set Body [CkXml_getChildContent $xml "Body|Message|Body"]
puts "$Body"

set cert [new_CkCert]

set success [CkCert_LoadPfxFile $cert "qa_data/pfx/govTalkMessage_aaa.pfx" "aaa"]
if {$success == 0} then {
    puts [CkCert_lastErrorText $cert]
    delete_CkXml $xml
    delete_CkCert $cert
    exit
}

set crypt [new_CkCrypt2]

CkCrypt2_put_CryptAlgorithm $crypt "pki"
set success [CkCrypt2_SetDecryptCert $crypt $cert]
if {$success == 0} then {
    puts [CkCrypt2_lastErrorText $crypt]
    delete_CkXml $xml
    delete_CkCert $cert
    delete_CkCrypt2 $crypt
    exit
}

set bd [new_CkBinData]

# Append the bytes to bd.
set success [CkBinData_AppendEncoded $bd $Body "base64"]

# Decrypt in-place.
set success [CkCrypt2_DecryptBd $crypt $bd]
if {$success == 0} then {
    puts [CkCrypt2_lastErrorText $crypt]
    delete_CkXml $xml
    delete_CkCert $cert
    delete_CkCrypt2 $crypt
    delete_CkBinData $bd
    exit
}

# Save the decrypted data to a file.
set success [CkBinData_WriteFile $bd "qa_output/out.dat"]

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

delete_CkXml $xml
delete_CkCert $cert
delete_CkCrypt2 $crypt
delete_CkBinData $bd