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

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();

crypt.EncodingMode = "hex";
crypt.HashAlgorithm = "sha-1";

string hashStr = crypt.HashFileENC("qa_data/hamlet.xml");
Debug.WriteLine("hash to sign: " + hashStr);

Chilkat.Dsa dsa = new Chilkat.Dsa();

string pemPrivateKey;
pemPrivateKey = dsa.LoadText("qa_data/dsa/dsaPrivKey2.pem");
bool success = dsa.FromPem(pemPrivateKey);
if (success == false) {
    Debug.WriteLine(dsa.LastErrorText);
    return;
}

// Load the hash to be signed into the DSA object:
success = dsa.SetEncodedHash("hex",hashStr);
if (success == false) {
    Debug.WriteLine(dsa.LastErrorText);
    return;
}

// Sign the hash.
success = dsa.SignHash();
if (success == false) {
    Debug.WriteLine(dsa.LastErrorText);
    return;
}

// Get the ASN.1 signature.
string asnSig = dsa.GetEncodedSignature("base64");
Debug.WriteLine("Signature: " + asnSig);

// Examine the details of the ASN.1 signature.
// We want to get the r,s values as hex strings..
Chilkat.Asn asn = new Chilkat.Asn();
success = asn.LoadEncoded(asnSig,"base64");
if (success == false) {
    Debug.WriteLine(asn.LastErrorText);
    return;
}

// Get the ASN.1 as XML.
Chilkat.Xml xml = new Chilkat.Xml();
success = xml.LoadXml(asn.AsnToXml());
Debug.WriteLine("Signature as XML: ");
Debug.WriteLine(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
string r = "2C187F3AB6E47A66497B86CE97BB39E2133810F5";
string s = "588E53D3F7B69636B48FD7175E99A3961BD7D775";

// Build the XML that will be converted to ASN.1
xml.Clear();
xml.Tag = "sequence";
xml.NewChild2("int",r);
xml.NewChild2("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("base64");

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

Chilkat.Dsa dsa2 = new Chilkat.Dsa();

// Load the DSA public key to be used for verification:
string pemPublicKey;
pemPublicKey = dsa2.LoadText("qa_data/dsa/dsaPubKey2.pem");
success = dsa2.FromPublicPem(pemPublicKey);
if (success == false) {
    Debug.WriteLine(dsa2.LastErrorText);
    return;
}

// Load the hash to be verified.
success = dsa2.SetEncodedHash("hex",hashStr);
if (success == false) {
    Debug.WriteLine(dsa2.LastErrorText);
    return;
}

// Load the ASN.1 signature:
success = dsa2.SetEncodedSignature("base64",asnSig);
if (success == false) {
    Debug.WriteLine(dsa2.LastErrorText);
    return;
}

// Verify:
success = dsa2.Verify();
if (success == false) {
    Debug.WriteLine(dsa2.LastErrorText);
}
else {
    Debug.WriteLine("DSA Signature Verified!");
}