(Java) DSA R,S Signature Values

See more DSA Examples

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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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkCrypt2 crypt = new CkCrypt2();

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

    String hashStr = crypt.hashFileENC("qa_data/hamlet.xml");
    System.out.println("hash to sign: " + hashStr);

    CkDsa dsa = new CkDsa();

    String pemPrivateKey;
    pemPrivateKey = dsa.loadText("qa_data/dsa/dsaPrivKey2.pem");
    boolean success = dsa.FromPem(pemPrivateKey);
    if (success == false) {
        System.out.println(dsa.lastErrorText());
        return;
        }

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

    // Sign the hash.
    success = dsa.SignHash();
    if (success == false) {
        System.out.println(dsa.lastErrorText());
        return;
        }

    // Get the ASN.1 signature.
    String asnSig = dsa.getEncodedSignature("base64");
    System.out.println("Signature: " + asnSig);

    // Examine the details of the ASN.1 signature.
    // We want to get the r,s values as hex strings..
    CkAsn asn = new CkAsn();
    success = asn.LoadEncoded(asnSig,"base64");
    if (success == false) {
        System.out.println(asn.lastErrorText());
        return;
        }

    // Get the ASN.1 as XML.
    CkXml xml = new CkXml();
    success = xml.LoadXml(asn.asnToXml());
    System.out.println("Signature as XML: ");
    System.out.println(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.put_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
    // --------------------------------------------------------------------

    CkDsa dsa2 = new CkDsa();

    // 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) {
        System.out.println(dsa2.lastErrorText());
        return;
        }

    // Load the hash to be verified.
    success = dsa2.SetEncodedHash("hex",hashStr);
    if (success == false) {
        System.out.println(dsa2.lastErrorText());
        return;
        }

    // Load the ASN.1 signature:
    success = dsa2.SetEncodedSignature("base64",asnSig);
    if (success == false) {
        System.out.println(dsa2.lastErrorText());
        return;
        }

    // Verify:
    success = dsa2.Verify();
    if (success == false) {
        System.out.println(dsa2.lastErrorText());
        }
    else {
        System.out.println("DSA Signature Verified!");
        }
  }
}