i am trying to encrypt some videos and then decrypting them later when required. the code works fine but since the key is generated randomly, if i encrypt a video and exit the application i wont be able to decrypt it again since next time when i open the application the keys are changed. I am using Gson to save my keys. but even that did not work.
The below is my encryption class code. Thanks in advance.
package com.example.videoplay;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.AlgorithmParameterSpec;
import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import com.google.gson.Gson;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Environment;
import android.preference.PreferenceManager;
import android.util.Log;
public class Encrypter {
Context contxt;
File inFile;
File outFile;
File outFile_dec;
SecretKey key;
byte[] keyData;
SecretKey key2;
byte[] iv;
AlgorithmParameterSpec paramSpec;
private final static int IV_LENGTH = 16; // Default length with Default 128
// key AES encryption
private final static int DEFAULT_READ_WRITE_BLOCK_BUFFER_SIZE = 1024;
private final static String ALGO_RANDOM_NUM_GENERATOR = "SHA1PRNG";
private final static String ALGO_SECRET_KEY_GENERATOR = "AES";
private final static String ALGO_VIDEO_ENCRYPTOR = "AES/CBC/PKCS5Padding";
public static String str_key,str_paramSpec,str_key2;
@SuppressWarnings("resource")
public static void encrypt(SecretKey key, AlgorithmParameterSpec paramSpec, InputStream in, OutputStream out)
throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException,
InvalidAlgorithmParameterException, IOException {
try {
byte[] iv = new byte[] { (byte) 0x8E, 0x12, 0x39, (byte) 0x9C,
0x07, 0x72, 0x6F, 0x5A, (byte) 0x8E, 0x12, 0x39, (byte) 0x9C,
0x07, 0x72, 0x6F, 0x5A };
paramSpec = new IvParameterSpec(iv);
Cipher c = Cipher.getInstance(ALGO_VIDEO_ENCRYPTOR);
c.init(Cipher.ENCRYPT_MODE, key, paramSpec);
out = new CipherOutputStream(out, c);
int count = 0;
byte[] buffer = new byte[DEFAULT_READ_WRITE_BLOCK_BUFFER_SIZE];
while ((count = in.read(buffer)) >= 0) {
out.write(buffer, 0, count);
}
} finally {
out.close();
}
}
@SuppressWarnings("resource")
public static void decrypt(SecretKey key, AlgorithmParameterSpec paramSpec, InputStream in, OutputStream out)
throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException,
InvalidAlgorithmParameterException, IOException {
try {
byte[] iv = new byte[] { (byte) 0x8E, 0x12, 0x39, (byte) 0x9C,
0x07, 0x72, 0x6F, 0x5A, (byte) 0x8E, 0x12, 0x39, (byte) 0x9C,
0x07, 0x72, 0x6F, 0x5A };
paramSpec = new IvParameterSpec(iv);
Cipher c = Cipher.getInstance(ALGO_VIDEO_ENCRYPTOR);
c.init(Cipher.DECRYPT_MODE, key, paramSpec);
out = new CipherOutputStream(out, c);
int count = 0;
byte[] buffer = new byte[DEFAULT_READ_WRITE_BLOCK_BUFFER_SIZE];
while ((count = in.read(buffer)) >= 0) {
out.write(buffer, 0, count);
}
} finally {
out.close();
}
}
public Encrypter(Context ctx) {
//
inFile = new File(Environment.getExternalStorageDirectory().getPath() +MainActivity.Directory+MainActivity.filename );
outFile = new File(Environment.getExternalStorageDirectory().getPath() + MainActivity.Directory+"/"+MainActivity.temponlyfilename);
outFile_dec = new File(Environment.getExternalStorageDirectory().getPath() + MainActivity.Directory+MainActivity.filename);
contxt=ctx;
try {
//........................................................................................
SharedPreferences mPrefs = PreferenceManager.getDefaultSharedPreferences(ctx);
String json = mPrefs.getString("pref_str_key", "empty");
if(json.equalsIgnoreCase("empty"))
{
key = KeyGenerator.getInstance(ALGO_SECRET_KEY_GENERATOR).generateKey();
keyData = key.getEncoded();
key2 = new SecretKeySpec(keyData, 0, keyData.length, ALGO_SECRET_KEY_GENERATOR); //if you want to store key bytes to db so its just how to //recreate back key from bytes array
iv = new byte[IV_LENGTH];
SecureRandom.getInstance(ALGO_RANDOM_NUM_GENERATOR).nextBytes(iv); // If
// storing
// separately
paramSpec = new IvParameterSpec(iv);
Editor prefsEditor = mPrefs.edit();
Gson gson = new Gson();
str_key = gson.toJson(key);
prefsEditor.putString("pref_str_key", str_key);
str_key2 = gson.toJson(2);
prefsEditor.putString("pref_str_key2", str_key2);
prefsEditor.commit();
}else
{
Gson gson = new Gson();
str_key = mPrefs.getString("pref_str_key", "");
key = gson.fromJson(str_key, SecretKey.class);
str_key2 = mPrefs.getString("pref_str_key2", "");
key2 = gson.fromJson(str_key2, SecretKey.class);
}
//........................................................................................
} catch (Exception e) {
e.printStackTrace();
}
}
public File Decrypt(File dir)
{
File dirout = new File(dir.getParent()+"/temp.ts");
try {
Encrypter.decrypt(key2, paramSpec, new FileInputStream(dir), new FileOutputStream(dirout));
outFile_dec.delete();
} catch (Exception e) {
e.printStackTrace();
}
return dirout;
}
public File Encrypt(File dir) {
File dirout = new File(dir.getParent()+"/temp.ts");
// TODO Auto-generated method stub
try {
Encrypter.encrypt(key, paramSpec, new FileInputStream(dir), new FileOutputStream(dirout));
dir.delete();
} catch (Exception e) {
e.printStackTrace();
}
return dirout;
}
public void DecryptFromTo(File dir,File dirout)
{
try {
Encrypter.decrypt(key2, paramSpec, new FileInputStream(dir), new FileOutputStream(dirout));
} catch (Exception e) {
e.printStackTrace();
}
}
}
