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. Chilkat2 Java

import com.chilkatsoft.chilkat2.Asn;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Crypt2;
import com.chilkatsoft.chilkat2.Dsa;
import com.chilkatsoft.chilkat2.Xml;

public class ChilkatExample {

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

        Crypt2 crypt = new Crypt2();

        crypt.setEncodingMode("hex");
        crypt.setHashAlgorithm("sha-1");

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

        Dsa dsa = new Dsa();

        String pemPrivateKey = dsa.loadText("qa_data/dsa/dsaPrivKey2.pem");
        try {
            dsa.fromPem(pemPrivateKey);

            // Load the hash to be signed into the DSA object:
            dsa.setEncodedHash("hex", hashStr);

            // Sign the hash.
            dsa.signHash();
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            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..
        Asn asn = new Asn();
        try {
            asn.loadEncoded(asnSig, "base64");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Get the ASN.1 as XML.
        Xml xml = new Xml();
        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.setTag("sequence");
        xml.newChild2("int", r);
        xml.newChild2("int", s);

        // Convert the XML to ASN.1
        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
        // --------------------------------------------------------------------

        Dsa dsa2 = new Dsa();

        // Load the DSA public key to be used for verification:
        String pemPublicKey = dsa2.loadText("qa_data/dsa/dsaPubKey2.pem");
        try {
            dsa2.fromPublicPem(pemPublicKey);

            // Load the hash to be verified.
            dsa2.setEncodedHash("hex", hashStr);

            // Load the ASN.1 signature:
            dsa2.setEncodedSignature("base64", asnSig);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Verify:
        try {
            dsa2.verify();
            System.out.println("DSA Signature Verified!");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
        }
    }
}