(Java) RSA Sign Binary Data and Verify (Recover the Original Data)

Demonstrates how to RSA sign binary data and then verify/recover the original data.

Note: This example uses methods introduced in Chilkat v9.5.0.77.

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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.

    // Load an RSA private key for signing.
    CkPrivateKey privKey = new CkPrivateKey();
    boolean success = privKey.LoadEncryptedPemFile("qa_data/pem/rsa_passwd.pem","passwd");
    if (success != true) {
        System.out.println(privKey.lastErrorText());
        return;
        }

    CkRsa rsa = new CkRsa();
    rsa.ImportPrivateKeyObj(privKey);

    // We have some binary data (in hex) to sign
    String originalData = "0102030405060708090A";
    CkBinData bd = new CkBinData();
    bd.AppendEncoded(originalData,"hex");

    // If successful, the contents of bd are replaced with the RSA signature.
    success = rsa.OpenSslSignBd(bd);
    if (success != true) {
        System.out.println(rsa.lastErrorText());
        return;
        }

    // Show the RSA signature in base64
    System.out.println(bd.getEncoded("base64"));

    // ------------------------------------------
    // Get the public key from the private key
    CkPublicKey pubKey = privKey.GetPublicKey();

    // Verify the signature and extract the original data.
    CkRsa rsa2 = new CkRsa();
    rsa2.ImportPublicKeyObj(pubKey);

    boolean bVerified = rsa2.OpenSslVerifyBd(bd);
    System.out.println("signature verified: " + bVerified);

    // Show the original data:
    System.out.println("original data: " + bd.getEncoded("hex"));
  }
}