public void putString(String key, String value) {
        if (mEditor == null) {
            mEditor = mPreferences.edit();
        }
        String obfuscatedValue = mObfuscator.obfuscate(value, key);
        mEditor.putString(key, obfuscatedValue);
    }
Constructor.

@param sp A SharedPreferences instance provided by the system.
@param o The Obfuscator to use when reading or writing data.
android/android_framework/base/src/main/java/com/google/android/vending/licensing/PreferenceObfuscator.java