Java

ECDSA Sign and Verify

See more ECC Examples

Demonstrates how to create an ECDSA signature on the SHA256 hash of some data, and then verify. Chilkat2 Java

import com.chilkatsoft.chilkat2.Asn;
import com.chilkatsoft.chilkat2.BinData;
import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Crypt2;
import com.chilkatsoft.chilkat2.Ecc;
import com.chilkatsoft.chilkat2.PrivateKey;
import com.chilkatsoft.chilkat2.Prng;
import com.chilkatsoft.chilkat2.PublicKey;
import com.chilkatsoft.chilkat2.Xml;

public class ChilkatExample {

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

        // First load an ECDSA private key to be used for signing.
        PrivateKey privKey = new PrivateKey();
        try {
            privKey.loadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem", "secret");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Sign the SHA256 hash of some data.
        BinData bd = new BinData();
        try {
            bd.loadFile("qa_data/hamlet.xml");
        } catch (ChilkatException e) {
            System.out.println("Failed to load file to be hashed.");
            return;
        }

        Crypt2 crypt = new Crypt2();
        crypt.setHashAlgorithm("sha256");
        crypt.setEncodingMode("base64");
        String hashStr = crypt.hashBdENC(bd);

        Ecc ecdsa = new Ecc();
        Prng prng = new Prng();
        // Returns ASN.1 signature as a base64 string.
        String sig = ecdsa.signHashENC(hashStr, "base64", privKey, prng);
        System.out.println("sig = " + sig);

        // The signature is in ASN.1 format (which may be described as the "encoded DSS signature").
        // SEQUENCE (2 elem)
        //   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
        //   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...

        // If you wish, you can get the r and s components of the signature like this:
        Asn asn = new Asn();
        asn.loadEncoded(sig, "base64");
        Xml xml = new Xml();
        xml.loadXml(asn.asnToXml());

        System.out.println(xml.getXml());

        // We now have this:
        // <?xml version="1.0" encoding="utf-8"?>
        // <sequence>
        //     <int>6650D422D86BA4A228B5617604E59052591B9B2C32EF324C44D09EF67E5F0060</int>
        //     <int>0CFD9F6AC85042FC70F672C141BA6B2A4CAFBB906C3D907BCCC1BED62B28326F</int>
        // </sequence>

        // Get the "r" and "s" as hex strings
        String r = xml.getChildContentByIndex(0);
        String s = xml.getChildContentByIndex(1);

        System.out.println("r = " + r);
        System.out.println("s = " + s);

        // --------------------------------------------------------------------
        // Now verify against the hash of the original data.

        // Get the corresponding public key.
        PublicKey pubKey = new PublicKey();
        try {
            pubKey.loadFromFile("qa_data/ecc/secp256r1-pub.pem");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
        Ecc ecc2 = new Ecc();
        int result = ecc2.verifyHashENC(hashStr, sig, "base64", pubKey);
        if (result != 1) {
            System.out.println(ecc2.getLastErrorText());
            return;
        }

        System.out.println("Verified!");

        // Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
        Xml xml2 = new Xml();
        xml2.setTag("sequence");
        xml2.newChild2("int", r);
        xml2.newChild2("int", s);

        Asn asn2 = new Asn();
        asn2.loadAsnXml(xml2.getXml());
        String encodedSig = asn2.getEncodedDer("base64");
        System.out.println("encoded DSS signature: " + encodedSig);

        // You can go to https://lapo.it/asn1js/  and copy/paste the base64 encodedSig into the online tool, then press the "decode" button.
        // You will see the ASN.1 such as this:

        // SEQUENCE (2 elem)
        //   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
        //   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...
    }
}