(Android™) RSA Encrypt and Decrypt Credit Card Numbers

Android™ sample code to RSA public-key encrypt and decrypt credit card numbers. The RSA key is loaded from an unencrypted PKCS8 file. Chilkat provides many ways of setting the key -- loading from both encrypted and unencrypted PEM, PKCS8, DER, PVK, etc. Keys may be loaded from files or in-memory representations. (The RSA component also provides the ability to generate RSA keys.)

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// 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();

    CkPrivateKey key = new CkPrivateKey();

    // Load an RSA private key from a file:
    boolean success = key.LoadAnyFormatFile("rsaPrivateKey.key","");
    if (success != true) {
        Log.i(TAG, key.lastErrorText());
        return;
        }

    // Get the key as XML:
    String keyXml;
    keyXml = key.getXml();

    // We'll encrypt with the public key and decrypt with the private
    // key.  (It's also possible to do the reverse.)
    // Note: An RSA private key is composed of different parts internally: modulus, exponent, P, Q, etc.
    // An RSA public-key is a sub-set of the private key.
    // Therefore, when you have a private key, you really have
    // both public and private keys.
    success = rsa.ImportPublicKey(keyXml);
    if (success != true) {
        Log.i(TAG, rsa.lastErrorText());
        return;
        }

    // Encrypt a VISA credit card number:
    // 1234-5678-0000-9999
    String ccNumber = "1234567800009999";

    boolean usePrivateKey = false;
    rsa.put_EncodingMode("base64");
    String encryptedStr = rsa.encryptStringENC(ccNumber,usePrivateKey);
    Log.i(TAG, "Encrypted:");
    Log.i(TAG, encryptedStr);

    // Now decrypt:
    CkRsa rsaDecryptor = new CkRsa();

    rsaDecryptor.put_EncodingMode("base64");
    success = rsaDecryptor.ImportPrivateKey(keyXml);

    usePrivateKey = true;
    String decryptedStr = rsaDecryptor.decryptStringENC(encryptedStr,usePrivateKey);

    Log.i(TAG, "Decrypted:");
    Log.i(TAG, decryptedStr);

    // Important: RSA encryption should only be used to encrypt small amounts of data.
    // It is typically used for encrypting symmetric encryption
    // keys such that a symmetric encryption algorithm, such as 
    // AES is then used to encrypt/decrypt bulk data

  }

  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."
  }
}