(Unicode C++) DSA R,S Signature Values

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Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature.

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#include <CkCrypt2W.h>
#include <CkDsaW.h>
#include <CkAsnW.h>
#include <CkXmlW.h>

void ChilkatSample(void)
    {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkCrypt2W crypt;

    crypt.put_EncodingMode(L"hex");
    crypt.put_HashAlgorithm(L"sha-1");

    const wchar_t *hashStr = crypt.hashFileENC(L"qa_data/hamlet.xml");
    wprintf(L"hash to sign: %s\n",hashStr);

    CkDsaW dsa;

    const wchar_t *pemPrivateKey = 0;
    pemPrivateKey = dsa.loadText(L"qa_data/dsa/dsaPrivKey2.pem");
    bool success = dsa.FromPem(pemPrivateKey);
    if (success == false) {
        wprintf(L"%s\n",dsa.lastErrorText());
        return;
    }

    // Load the hash to be signed into the DSA object:
    success = dsa.SetEncodedHash(L"hex",hashStr);
    if (success == false) {
        wprintf(L"%s\n",dsa.lastErrorText());
        return;
    }

    // Sign the hash.
    success = dsa.SignHash();
    if (success == false) {
        wprintf(L"%s\n",dsa.lastErrorText());
        return;
    }

    // Get the ASN.1 signature.
    const wchar_t *asnSig = dsa.getEncodedSignature(L"base64");
    wprintf(L"Signature: %s\n",asnSig);

    // Examine the details of the ASN.1 signature.
    // We want to get the r,s values as hex strings..
    CkAsnW asn;
    success = asn.LoadEncoded(asnSig,L"base64");
    if (success == false) {
        wprintf(L"%s\n",asn.lastErrorText());
        return;
    }

    // Get the ASN.1 as XML.
    CkXmlW xml;
    success = xml.LoadXml(asn.asnToXml());
    wprintf(L"Signature as XML: \n");
    wprintf(L"%s\n",xml.getXml());

    // Sample XML shown here.
    // The r and s values are the two hex strings in the XML.

    // <?xml version="1.0" encoding="utf-8"?>
    // <sequence>
    //     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
    //     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
    // </sequence>

    // Pretend we're starting with r,s
    const wchar_t *r = L"2C187F3AB6E47A66497B86CE97BB39E2133810F5";
    const wchar_t *s = L"588E53D3F7B69636B48FD7175E99A3961BD7D775";

    // Build the XML that will be converted to ASN.1
    xml.Clear();
    xml.put_Tag(L"sequence");
    xml.NewChild2(L"int",r);
    xml.NewChild2(L"int",s);

    // Convert the XML to ASN.1
    success = asn.LoadAsnXml(xml.getXml());

    // Emit the signature as DER encoded ASN.1 (base64)
    asnSig = asn.getEncodedDer(L"base64");

    // --------------------------------------------------------------------
    // Verify the signature using the asnSig we built from the r,s values
    // --------------------------------------------------------------------

    CkDsaW dsa2;

    // Load the DSA public key to be used for verification:
    const wchar_t *pemPublicKey = 0;
    pemPublicKey = dsa2.loadText(L"qa_data/dsa/dsaPubKey2.pem");
    success = dsa2.FromPublicPem(pemPublicKey);
    if (success == false) {
        wprintf(L"%s\n",dsa2.lastErrorText());
        return;
    }

    // Load the hash to be verified.
    success = dsa2.SetEncodedHash(L"hex",hashStr);
    if (success == false) {
        wprintf(L"%s\n",dsa2.lastErrorText());
        return;
    }

    // Load the ASN.1 signature:
    success = dsa2.SetEncodedSignature(L"base64",asnSig);
    if (success == false) {
        wprintf(L"%s\n",dsa2.lastErrorText());
        return;
    }

    // Verify:
    success = dsa2.Verify();
    if (success == false) {
        wprintf(L"%s\n",dsa2.lastErrorText());
    }
    else {
        wprintf(L"DSA Signature Verified!\n");
    }
    }