ObscuredSharedPreferences.java by RightHandedMonkey

gistfile1.java

import java.io.UnsupportedEncodingException;
import java.util.Map;
import java.util.Set;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;

import com.worxforus.Base64Support;

import android.content.Context;
import android.content.SharedPreferences;
import android.provider.Settings;
import android.provider.Settings.Secure;
import android.util.Log;


/**
 * Taken from https://github.com/RightHandedMonkey/WorxForUs_Library/blob/master/src/com/worxforus/android/ObscuredSharedPreferences.java
 * Thanks to emmby at http://stackoverflow.com/questions/785973/what-is-the-most-appropriate-way-to-store-user-settings-in-android-application/6393502#6393502
 * 
 * Documentation: http://right-handed-monkey.blogspot.com/2014/04/obscured-shared-preferences-for-android.html
 * This class has the following additions over the original:
 *  additional logic for handling the case for when the preferences were not originally encrypted, but now are.
 *  The secret key is no longer hard coded, but defined at runtime based on the individual device.  
 *  The benefit is that if one device is compromised, it now only affects that device.
 * 
 * Simply replace your own SharedPreferences object in this one, and any data you read/write will be automatically encrypted and decrypted.
 * 
 * Updated usage:
 *    ObscuredSharedPreferences prefs = ObscuredSharedPreferences.getPrefs(this, MY_APP_NAME, Context.MODE_PRIVATE);
 *    //to get data
 *    prefs.getString("foo", null);
 *    //to store data
 *    prefs.edit().putString("foo","bar").commit();
 */
public class ObscuredSharedPreferences implements SharedPreferences {
    protected static final String UTF8 = "UTF-8";
    //this key is defined at runtime based on ANDROID_ID which is supposed to last the life of the device
    private static char[] SEKRIT=null; 
    private static byte[] SALT=null;
    
    private static char[] backup_secret=null;
    private static byte[] backup_salt=null;

    protected SharedPreferences delegate;
    protected Context context;
    private static ObscuredSharedPreferences prefs = null;
    
    //Set to true if a decryption error was detected
    //in the case of float, int, and long we can tell if there was a parse error
    //this does not detect an error in strings or boolean - that requires more sophisticated checks
    public static boolean decryptionErrorFlag = false; 
  
    /**
     * Constructor
     * @param context
     * @param delegate - SharedPreferences object from the system
     */
    public ObscuredSharedPreferences(Context context, SharedPreferences delegate) {
        this.delegate = delegate;
        this.context = context;
        //updated thanks to help from bkhall on github
        ObscuredSharedPreferences.setNewKey(Settings.Secure.getString(context.getContentResolver(), Settings.Secure.ANDROID_ID));
        ObscuredSharedPreferences.setNewSalt(Settings.Secure.getString(context.getContentResolver(), Settings.Secure.ANDROID_ID));
    }
    
    /**
     * Only used to change to a new key during runtime.
     * If you don't want to use the default per-device key for example
     * @param key
     */
    public static void setNewKey(String key) {
    	SEKRIT = key.toCharArray();
    }
    
    /**
     * Only used to change to a new salt during runtime.
     * If you don't want to use the default per-device code for example
     * @param salt - this must be a string in UT
     */
    public static void setNewSalt(String salt) {
    	try {
			SALT = salt.getBytes(UTF8);
		} catch (UnsupportedEncodingException e) {
	        throw new RuntimeException(e);
		}
    }

    /**
     * Accessor to grab the preferences in a singleton.  This stores the reference in a singleton so it can be accessed repeatedly with 
     * no performance penalty
     * @param c - the context used to access the preferences.
     * @param appName - domain the shared preferences should be stored under
     * @param contextMode - Typically Context.MODE_PRIVATE
     * @return
     */
    public synchronized static ObscuredSharedPreferences getPrefs(Context c, String appName, int contextMode) {
    	if (prefs == null) {
    		//make sure to use application context since preferences live outside an Activity
    		//use for objects that have global scope like: prefs or starting services
	    		prefs = new ObscuredSharedPreferences( 
	       			 c.getApplicationContext(), c.getApplicationContext().getSharedPreferences(appName, contextMode) );
    	}
    	return prefs;
    }
    
    public class Editor implements SharedPreferences.Editor {
        protected SharedPreferences.Editor delegate;

        public Editor() {
            this.delegate = ObscuredSharedPreferences.this.delegate.edit();                    
        }

        @Override
        public Editor putBoolean(String key, boolean value) {
            delegate.putString(key, encrypt(Boolean.toString(value)));
            return this;
        }

        @Override
        public Editor putFloat(String key, float value) {
            delegate.putString(key, encrypt(Float.toString(value)));
            return this;
        }

        @Override
        public Editor putInt(String key, int value) {
            delegate.putString(key, encrypt(Integer.toString(value)));
            return this;
        }

        @Override
        public Editor putLong(String key, long value) {
            delegate.putString(key, encrypt(Long.toString(value)));
            return this;
        }

        @Override
        public Editor putString(String key, String value) {
            delegate.putString(key, encrypt(value));
            return this;
        }

        @Override
        public void apply() {
        	//to maintain compatibility with android level 7 
        	delegate.commit();
        }

        @Override
        public Editor clear() {
            delegate.clear();
            return this;
        }

        @Override
        public boolean commit() {
            return delegate.commit();
        }

        @Override
        public Editor remove(String s) {
            delegate.remove(s);
            return this;
        }

		@Override
		public android.content.SharedPreferences.Editor putStringSet(String key, Set<String> values) {
			throw new RuntimeException("This class does not work with String Sets.");
		}
    }

    public Editor edit() {
        return new Editor();
    }


    @Override
    public Map<String, ?> getAll() {
        throw new UnsupportedOperationException(); // left as an exercise to the reader
    }
    
    @Override
    public boolean getBoolean(String key, boolean defValue) {
    	//if these weren't encrypted, then it won't be a string
    	String v;
    	try {
			v = delegate.getString(key, null);
    	} catch (ClassCastException e) {
    		return delegate.getBoolean(key, defValue);
    	}
    	//Boolean string values should be 'true' or 'false'
    	//Boolean.parseBoolean does not throw a format exception, so check manually
    	String parsed = decrypt(v);
    	if (!checkBooleanString(parsed) ) {
    		//could not decrypt the Boolean.  Maybe the wrong key was used.
			decryptionErrorFlag = true;
        	Log.e(this.getClass().getName(), "Warning, could not decrypt the value.  Possible incorrect key used.");
    	}
        return v!=null ? Boolean.parseBoolean(parsed) : defValue;
    }

    /**
     * This function checks if a valid string is received on a request for a Boolean object
     * @param str
     * @return
     */
    private boolean checkBooleanString(String str) {
    	return ("true".equalsIgnoreCase(str) || "false".equalsIgnoreCase(str)); 
    }

    @Override
    public float getFloat(String key, float defValue) {
    	String v;
    	try {
			v = delegate.getString(key, null);
    	} catch (ClassCastException e) {
    		return delegate.getFloat(key, defValue);
    	}
    	try {
			return Float.parseFloat(decrypt(v));
		} catch (NumberFormatException e) {
			//could not decrypt the number.  Maybe we are using the wrong key?
			decryptionErrorFlag = true;
        	Log.e(this.getClass().getName(), "Warning, could not decrypt the value.  Possible incorrect key.  "+e.getMessage());
		}
    	return defValue;
    }

    @Override
    public int getInt(String key, int defValue) {
    	String v;
    	try {
			v = delegate.getString(key, null);
    	} catch (ClassCastException e) {
    		return delegate.getInt(key, defValue);
    	}
    	try {
			return Integer.parseInt(decrypt(v));
		} catch (NumberFormatException e) {
			//could not decrypt the number.  Maybe we are using the wrong key?
			decryptionErrorFlag = true;
        	Log.e(this.getClass().getName(), "Warning, could not decrypt the value.  Possible incorrect key.  "+e.getMessage());
		}
    	return defValue;
    }

    @Override
    public long getLong(String key, long defValue) {
    	String v;
    	try {
			v = delegate.getString(key, null);
    	} catch (ClassCastException e) {
    		return delegate.getLong(key, defValue);
    	}
    	try {
			return Long.parseLong(decrypt(v));
		} catch (NumberFormatException e) {
			//could not decrypt the number.  Maybe we are using the wrong key?
			decryptionErrorFlag = true;
        	Log.e(this.getClass().getName(), "Warning, could not decrypt the value.  Possible incorrect key.  "+e.getMessage());
		}
    	return defValue;
    }

    @Override
    public String getString(String key, String defValue) {
        final String v = delegate.getString(key, null);
        return v != null ? decrypt(v) : defValue;
    }

    @Override
    public boolean contains(String s) {
        return delegate.contains(s);
    }

    @Override
    public void registerOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener onSharedPreferenceChangeListener) {
        delegate.registerOnSharedPreferenceChangeListener(onSharedPreferenceChangeListener);
    }

    @Override
    public void unregisterOnSharedPreferenceChangeListener(OnSharedPreferenceChangeListener onSharedPreferenceChangeListener) {
        delegate.unregisterOnSharedPreferenceChangeListener(onSharedPreferenceChangeListener);
    }

	@Override
	public Set<String> getStringSet(String key, Set<String> defValues) {
		throw new RuntimeException("This class does not work with String Sets.");
	}

	/**
	 * Push key allows you to hold the current key being used into a holding location so that it can be retrieved later
	 * The use case is for when you need to load a new key, but still want to restore the old one.
	 */
	public static void pushKey() {
		backup_secret = SEKRIT;
	}
	
	/**
	 * This takes the key previously saved by pushKey() and activates it as the current decryption key
	 */
	public static void popKey() {
		SEKRIT = backup_secret;
	}
	
	/**
	 * pushSalt() allows you to hold the current salt being used into a holding location so that it can be retrieved later
	 * The use case is for when you need to load a new salt, but still want to restore the old one.
	 */
	public static void pushSalt() {
		backup_salt = SALT;
	}
	
	/**
	 * This takes the value previously saved by pushSalt() and activates it as the current salt
	 */
	public static void popSalt() {
		SALT = backup_salt;
	}
	
    protected String encrypt( String value ) {

        try {
            final byte[] bytes = value!=null ? value.getBytes(UTF8) : new byte[0];
            SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
            SecretKey key = keyFactory.generateSecret(new PBEKeySpec(SEKRIT));
            Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
            pbeCipher.init(Cipher.ENCRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
            return new String(Base64Support.encode(pbeCipher.doFinal(bytes), Base64Support.NO_WRAP),UTF8);
        } catch( Exception e ) {
            throw new RuntimeException(e);
        }

    }

    protected String decrypt(String value){
        try {
            final byte[] bytes = value!=null ? Base64Support.decode(value,Base64Support.DEFAULT) : new byte[0];
            SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
            SecretKey key = keyFactory.generateSecret(new PBEKeySpec(SEKRIT));
            Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
            pbeCipher.init(Cipher.DECRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
            return new String(pbeCipher.doFinal(bytes),UTF8);
        } catch( Exception e) {
        	Log.e(this.getClass().getName(), "Warning, could not decrypt the value.  It may be stored in plaintext.  "+e.getMessage());
        	return value;
        }
    }
}