(C) 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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#include <C_CkHttp.h>
#include <C_CkStringBuilder.h>
#include <C_CkPrivateKey.h>
#include <C_CkXmlDSigGen.h>
#include <C_CkXmlDSig.h>

void ChilkatSample(void)
    {
    const char *url;
    HCkHttp http;
    HCkStringBuilder sbXml;
    BOOL success;
    HCkPrivateKey dsaKey;
    HCkXmlDSigGen xmlSigGen;
    HCkXmlDSig verifier;
    BOOL bVerified;

    // 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..

    url = "https://www.chilkatsoft.com/exampleData/xmlToSign.xml";
    http = CkHttp_Create();
    sbXml = CkStringBuilder_Create();
    success = CkHttp_QuickGetSb(http,url,sbXml);
    if (success != TRUE) {
        printf("%s\n",CkHttp_lastErrorText(http));
        CkHttp_Dispose(http);
        CkStringBuilder_Dispose(sbXml);
        return;
    }

    // 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".
    dsaKey = CkPrivateKey_Create();
    success = CkPrivateKey_LoadEncryptedPemFile(dsaKey,"qa_data/dsa/dsa1024_secret.pem","secret");
    if (success != TRUE) {
        printf("%s\n",CkPrivateKey_lastErrorText(dsaKey));
        CkHttp_Dispose(http);
        CkStringBuilder_Dispose(sbXml);
        CkPrivateKey_Dispose(dsaKey);
        return;
    }

    // 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.
    // 

    xmlSigGen = CkXmlDSigGen_Create();

    // 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.
    CkXmlDSigGen_putSigLocation(xmlSigGen,"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.
    CkXmlDSigGen_AddSameDocRef(xmlSigGen,"abc","sha1","EXCL_C14N","","");

    // Provide the DSA key to be used for signing:
    CkXmlDSigGen_SetPrivateKey(xmlSigGen,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.
    CkXmlDSigGen_putSignedInfoDigestMethod(xmlSigGen,"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 = CkXmlDSigGen_CreateXmlDSigSb(xmlSigGen,sbXml);
    if (success != TRUE) {
        printf("%s\n",CkXmlDSigGen_lastErrorText(xmlSigGen));
        CkHttp_Dispose(http);
        CkStringBuilder_Dispose(sbXml);
        CkPrivateKey_Dispose(dsaKey);
        CkXmlDSigGen_Dispose(xmlSigGen);
        return;
    }

    // Examine the signed XML:
    printf("%s\n",CkStringBuilder_getAsString(sbXml));

    // 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:

    verifier = CkXmlDSig_Create();

    // First load the XML containing the signature(s) to be verified.
    success = CkXmlDSig_LoadSignatureSb(verifier,sbXml);
    if (success != TRUE) {
        printf("%s\n",CkXmlDSig_lastErrorText(verifier));
        CkHttp_Dispose(http);
        CkStringBuilder_Dispose(sbXml);
        CkPrivateKey_Dispose(dsaKey);
        CkXmlDSigGen_Dispose(xmlSigGen);
        CkXmlDSig_Dispose(verifier);
        return;
    }

    bVerified = CkXmlDSig_VerifySignature(verifier,TRUE);
    if (bVerified != TRUE) {
        printf("%s\n",CkXmlDSig_lastErrorText(verifier));
    }

    printf("Signature verified = %d\n",bVerified);


    CkHttp_Dispose(http);
    CkStringBuilder_Dispose(sbXml);
    CkPrivateKey_Dispose(dsaKey);
    CkXmlDSigGen_Dispose(xmlSigGen);
    CkXmlDSig_Dispose(verifier);

    }