(Android™) Generate RSA Key and Sign a String

See more RSA Examples

Demonstrates how to generate a new RSA public/private key pair and use it to generate a signature for a string. The (binary) digital signature is returned as a hexidecimalized string.

Chilkat Android™ Downloads Android™ Java Libraries Android C/C++ Libraries

// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // This example assumes the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkRsa rsa = new CkRsa();

    // Generate a 2048-bit RSA key.
    boolean success = rsa.GenerateKey(2048);

    // To return the signature in hex.
    rsa.put_EncodingMode("hex");

    String strData = "This is the string to be signed.";

    // Sign the SHA256 hash of the string.
    String hexSig = rsa.signStringENC(strData,"sha256");

    Log.i(TAG, hexSig);
    Log.i(TAG, rsa.lastErrorText());

    // Now verify the signature:
    success = rsa.VerifyStringENC(strData,"sha256",hexSig);
    if (success == true) {
        Log.i(TAG, "Signature verified!");
        }
    else {
        Log.i(TAG, rsa.lastErrorText());
        }

    // Try it with an invalid signature:
    success = rsa.VerifyStringENC(strData,"sha256","not a valid sig");
    if (success == true) {
        Log.i(TAG, "Signature verified!");
        }
    else {
        Log.i(TAG, rsa.lastErrorText());
        }

    // Try it with invalid data:
    success = rsa.VerifyStringENC("Not the original data","sha256",hexSig);
    if (success == true) {
        Log.i(TAG, "Signature verified!");
        }
    else {
        Log.i(TAG, rsa.lastErrorText());
        }

    // Try it with the wrong hash algorithm:
    success = rsa.VerifyStringENC(strData,"sha-1",hexSig);
    if (success == true) {
        Log.i(TAG, "Signature verified!");
        }
    else {
        Log.i(TAG, rsa.lastErrorText());
        }


  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}