(Visual Basic 6.0) Create XML Digital Signature using a DSA Key

Demonstrates how to create an XML digital signature using a DSA key.

This example requires Chilkat v9.5.0.69 or greater.

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

' The XML to be signed in this example contains the following:

' <?xml version="1.0" encoding="UTF-8" standalone="no"?>
' <Envelope>
'   <Header>
'     <Security>
'     </Security>
'   </Header>
'   <Body Id="abc">
'     <z:FooBar xmlns:z="https://www.example-code.com"/>
'   </Body>
' </Envelope>

' The above XML is available at https://www.chilkatsoft.com/exampleData/xmlToSign.xml
' Fetch the XML and then sign it..

Dim url As String
url = "https://www.chilkatsoft.com/exampleData/xmlToSign.xml"
Dim http As New ChilkatHttp
Dim sbXml As New ChilkatStringBuilder
Dim success As Long
success = http.QuickGetSb(url,sbXml)
If (success <> 1) Then
    Debug.Print http.LastErrorText
    Exit Sub
End If

' This example uses a DSA private key for signing.  
' There are many ways of getting an DSA private key using Chilkat.  This example
' will load it from an encrypted PEM file.

' In case you would like to use it, I put the DSA private key PEM file here:
' https://www.chilkatsoft.com/exampleData/dsa1024_secret.zip
' The password is "secret".
Dim dsaKey As New PrivateKey
success = dsaKey.LoadEncryptedPemFile("qa_data/dsa/dsa1024_secret.pem","secret")
If (success <> 1) Then
    Debug.Print dsaKey.LastErrorText
    Exit Sub
End If

' To create the XML digital signature (i.e. embed the signature within
' the XML), first specify what is desired, then call the method to 
' create the XML signature.
' 
' For example, the application must provide the following:
'     - Where to put the signature.
'     - What to sign.
'     - The algorithms to be used.
'     - The key to be used for signing.
' 

Dim xmlSigGen As New ChilkatXmlDSigGen

' In this example, we're going to put the signature within the Security element.
' To specify the location, set the SigLocation property to the XML path to this element,
' using vertical bar characters to separate tags.
xmlSigGen.SigLocation = "Envelope|Header|Security"

' An XML digital signature contains one or more references.  These can be references to the parts
' of the XML document to be signed (a same document reference), or can be external references.
' This example will add a single same-document reference.  We'll add a reference to the XML fragment
' at Body, which is indicated by providing the value of the "ID" attribute (where "ID" is case
' insensitive).  In this case, we specify "abc" because Body has an Id="abc".
' This causes the <Body> ... </Body> XML fragment to be signed.
' 
' For each same-document reference, we must also indicate the hash algorithm and XML canonicalization
' algorithm to be used.  For this example we'll choose SHA1 and Exclusive XML Canonicalization.
success = xmlSigGen.AddSameDocRef("abc","sha1","EXCL_C14N","","")

' Provide the DSA key to be used for signing:
success = xmlSigGen.SetPrivateKey(dsaKey)

' We're leaving the following properties at their default values:
' 
'    - SigNamespacePrefix (default is "ds")
'    - SignedInfoCanonAlg  (default is EXCL_C14N)
'    - KeyInfoType (default is "KeyValue", where the DSA public key is included in the Signature)

' Note: Each Reference has it's own specified algorithms for XML canonicalization and hashing,
' and the actual signature part (the SignedInfo) has it's own hash/canonicalization algorithm.
' They may or may not be the same.  In this example, we use Exclusive XML Canonicalization and SHA1 throughout.

' The default SignedInfoDigestMethod is sha256, which is a good choice.  This example will
' change it to sha1.
xmlSigGen.SignedInfoDigestMethod = "sha1"

' OK, everything's specified, so let's create the XML digital signature:
' This in-place signs the XML.  If successful, sbXml will contain the 
' XML with the digital signature at the specified location.
success = xmlSigGen.CreateXmlDSigSb(sbXml)
If (success <> 1) Then
    Debug.Print xmlSigGen.LastErrorText
    Exit Sub
End If

' Examine the signed XML:
Debug.Print sbXml.GetAsString()

' Below is the signed XML that is produced.
' Chilkat emits the Signature in compact form on a single line.  Whitespace in XML signatures
' matters.  Chilkat's opinion is that writing the Signature without whitespace minimizes the chance
' for problems with whatever software might be verifying the signature.

' <?xml version="1.0" encoding="UTF-8" standalone="no"?>
' <Envelope>
'   <Header>
'     <Security>
'     <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#"><ds:SignedInfo><ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/><ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#dsa-sha1"/><ds:Reference URI="#abc"><ds:Transforms><ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/></ds:Transforms><ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/><ds:DigestValue>77X3L6odxTBow1W1dIiqZW1foow=</ds:DigestValue></ds:Reference></ds:SignedInfo><ds:SignatureValue>Ci/KiAqoQLvNyK94n8TJwdJ6dVpIIy8tJg+9s8utmB92cW8lTd+U7g==</ds:SignatureValue><ds:KeyInfo><ds:KeyValue><ds:DSAKeyValue><ds:P>AN+Af9FvnqYl84Own8m/MHza9vVFEbpySOiWyeIM8diDjaES9i+UykaX9BGc0oaRJHtrHhe+gboMBGHfP+gYcgbqzeyVCi2kHghRD/TK7uI4jN8Yv8tfM6AO0QrDFfxFq4IV+qTZbSoCkbWaopQ+kEOY6B4btFxJ1YuE48mExMZ3</ds:P><ds:Q>AOCv5pwf4kvMW37Yzt0iH6URKOlD</ds:Q><ds:G>FO3eoDcpuU9Z25OQGFtC+M2ifczcKyRkFwTauGR3mIw0wePPiu3Ocr7A81SA8GQ9x3hWO5jyP//jL3jxYy8fgBg2RXwiic3nwT2rZfu50g6tPUpz1stKz/+Mxjulo6XuaMSOWwjU021IxVMzxQ1/L8QiwiIrwxvfQOaMY8HJgvw=</ds:G><ds:Y>JJmZQvWtrZ+Nb2YV47SfGAave8uOIedGlmg+CseoqKZC2aFcWM6kR0giUwQx834dhxQScRhqzxFxQPk/x+5hyG8LQbXW+BELmT1BiyodobYUAet4rSIt4EU4KU0iYw1drpcWT1jqI07l5xNi28heYSfSF5Odv2qwXxVKDSEeEkM=</ds:Y></ds:DSAKeyValue></ds:KeyValue></ds:KeyInfo></ds:Signature></Security>
'   </Header>
'   <Body Id="abc">
'     <z:FooBar xmlns:z="https://www.example-code.com"/>
'   </Body>
' </Envelope>

' The above signed XML contains the DSA public key in the DSAKeyValue fragment (within the ds:KeyInfo).
' The signature can easily be verified like this:

Dim verifier As New ChilkatXmlDSig

' First load the XML containing the signature(s) to be verified.
success = verifier.LoadSignatureSb(sbXml)
If (success <> 1) Then
    Debug.Print verifier.LastErrorText
    Exit Sub
End If

Dim bVerified As Long
bVerified = verifier.VerifySignature(1)
If (bVerified <> 1) Then
    Debug.Print verifier.LastErrorText
End If

Debug.Print "Signature verified = " & bVerified