Java

DSA Signature Create and Verify

See more DSA Examples

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

Java

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[])
  {
    boolean success = false;

    // 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");

    // Return the SHA-1 hash of a file.  The file may be any size.
    // The Chilkat Crypt component will stream the file when 
    // computing the hash, keeping the memory usage constant
    // and reasonable.
    // The 20-byte SHA-1 hash is returned as a hex-encoded string.
    String hashStr = crypt.hashFileENC("hamlet.xml");

    CkDsa dsa = new CkDsa();

    // Load a DSA private key from a PEM file.  Chilkat DSA
    // provides the ability to load and save DSA public and private
    // keys from encrypted or non-encrypted PEM or DER.
    // The LoadText method is for convenience only.  You may
    // use any means to load the contents of a PEM file into
    // a string.
    String pemPrivateKey;
    pemPrivateKey = dsa.loadText("dsa_priv.pem");
    success = dsa.FromPem(pemPrivateKey);
    if (success != true) {
        System.out.println(dsa.lastErrorText());
        return;
        }

    // You may optionally verify the key to ensure that it is a valid
    // DSA key.
    success = dsa.VerifyKey();
    if (success != true) {
        System.out.println(dsa.lastErrorText());
        return;
        }

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

    // Now that the DSA object contains both the private key and hash,
    // it is ready to create the signature:
    success = dsa.SignHash();
    if (success != true) {
        System.out.println(dsa.lastErrorText());
        return;
        }

    // If SignHash is successful, the DSA object contains the
    // signature.  It may be accessed as a hex or base64 encoded
    // string.  (It is also possible to access directly in byte array form via
    // the "Signature" property.)
    String hexSig = dsa.getEncodedSignature("hex");
    System.out.println("Signature:");
    System.out.println(hexSig);

    // -----------------------------------------------------------
    // Step 2: Verify the DSA Signature
    // -----------------------------------------------------------

    CkDsa dsa2 = new CkDsa();

    // Load the DSA public key to be used for verification:
    String pemPublicKey;
    pemPublicKey = dsa2.loadText("dsa_pub.pem");
    success = dsa2.FromPublicPem(pemPublicKey);
    if (success != true) {
        System.out.println(dsa2.lastErrorText());
        return;
        }

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

    // Load the signature:
    success = dsa2.SetEncodedSignature("hex",hexSig);
    if (success != true) {
        System.out.println(dsa2.lastErrorText());
        return;
        }

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