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(Java) ECDSA Sign and Verify

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

Chilkat Java Downloads

Java Libs for Windows, MacOS, Linux, Alpine Linux, Solaris

Java Libs for Android

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 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.
    CkPrivateKey privKey = new CkPrivateKey();
    boolean success = privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret");
    if (success == false) {
        System.out.println(privKey.lastErrorText());
        return;
        }

    // Sign the SHA256 hash of some data.
    CkBinData bd = new CkBinData();
    success = bd.LoadFile("qa_data/hamlet.xml");
    if (success == false) {
        System.out.println("Failed to load file to be hashed.");
        return;
        }

    CkCrypt2 crypt = new CkCrypt2();
    crypt.put_HashAlgorithm("sha256");
    crypt.put_EncodingMode("base64");
    String hashStr = crypt.hashBdENC(bd);

    CkEcc ecdsa = new CkEcc();
    CkPrng prng = new CkPrng();
    // 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:
    CkAsn asn = new CkAsn();
    asn.LoadEncoded(sig,"base64");
    CkXml xml = new CkXml();
    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.
    CkPublicKey pubKey = new CkPublicKey();
    success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem");
    if (success == false) {
        System.out.println(pubKey.lastErrorText());
        return;
        }

    // We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
    CkEcc ecc2 = new CkEcc();
    int result = ecc2.VerifyHashENC(hashStr,sig,"base64",pubKey);
    if (result != 1) {
        System.out.println(ecc2.lastErrorText());
        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:
    CkXml xml2 = new CkXml();
    xml2.put_Tag("sequence");
    xml2.NewChild2("int",r);
    xml2.NewChild2("int",s);

    CkAsn asn2 = new CkAsn();
    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...
  }
}

 

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