(Android™) Decrypt 256-bit AES GCM Produced by Something Unknown

Demonstrates how to decrypt something produced elsewhere (unknown) with 256-bit AES GCM.

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.

    // We have the following to decrypt:

    // Key (Base64): 
    String keyBase64 = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

    // IV (Base64Url):
    String ivBase64Url = "xrvaINMLqotAbWRK";

    // ciphertext (base64url):
    String cipherBase64Url = "RtGNAS-zQOxSB8W0HfqJjCoyt9KgImW_l-HjVC40hOOl-RNfRF3hzDIT1kvFVF8i_KX9XmqAftb6lyq-jLCEc_MSgqt3q1ixv3Ez4SbS3G5e3qGzLwxIMi2sCt00aDNwK2ipsJ4aw8s7ePPnl4oY-y1st9rwCWR0rrgEZwS9jmS4uJWGPn9K3jbKRnMslznDbtFLNJctMVXBTP-cv47JelxLCBOQSlK29rMuEFrhHR_VQrPq6gtZaBVSXZSYT0XOklp7nu9mVhrMCRtBCC5oiu5MPE5JYx4ANo3hUY7_NyQl2bpn9GfRXrdvqRGE-gy2upj-cDkm0t_tV8xmYge9DBQTH3B_4BGl2qTk_o-m7pEmKkS8XSdQhGcuFlykqrkE8SzB5I8esfzWOM0pwxbz0H_VaylKYHY=";

    CkCrypt2 crypt = new CkCrypt2();

    crypt.put_CryptAlgorithm("aes");
    crypt.put_CipherMode("gcm");
    crypt.put_KeyLength(256);

    boolean success = crypt.SetEncodedAad("random","ascii");
    crypt.SetEncodedKey(keyBase64,"base64");
    crypt.SetEncodedIV(ivBase64Url,"base64url");

    // The cipher text contains the 16-byte auth tag at the end.
    // get it separately..
    CkBinData bdEncrypted = new CkBinData();
    CkBinData bdAuthTag = new CkBinData();
    success = bdEncrypted.AppendEncoded(cipherBase64Url,"base64url");

    int numBytes = bdEncrypted.get_NumBytes();
    String authTagHex = bdEncrypted.getEncodedChunk(numBytes - 16,16,"hex");

    Log.i(TAG, "Auth tag in hex: " + authTagHex);

    success = bdAuthTag.AppendEncoded(authTagHex,"hex");
    bdEncrypted.RemoveChunk(numBytes - 16,16);

    // Use this special value to tell Chilkat to ignore the auth tag.
    success = crypt.SetEncodedAuthTag("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF","hex");

    // Decrypt
    crypt.put_EncodingMode("base64");
    String originalText = crypt.decryptStringENC(bdEncrypted.getEncoded("base64"));
    if (crypt.get_LastMethodSuccess() == false) {
        Log.i(TAG, crypt.lastErrorText());
        }
    else {
        Log.i(TAG, originalText);
        Log.i(TAG, "Success.");
        }

    // Decrypted text

  }

  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."
  }
}