I'm making an Android app that generates an Excel file using JExcelApi. The content of the fiel is also available as plain text but it's not stored anywhere (I'm using it for displaying it on a TextView; the content isn't too complex).
To simplify things I store the Excel file on the SD card root directory. I know it's not good practice, but this app is not meant for wide distribution and it's only used for internal purposes in my company, so I'm not too worried about it. When the app generates the file, you can either press a "send XLS" button on the main view which will create a SEND_ACTION intent so you can send the file through email, Dropbox or whatever, or you can just simply plug the phone to a computer, mount it as USB storage and get the file.
However, soon we're going to need to send the app to some of our clients and some changes need to be done. We don't want our clients to access the XLS file, so I need to protect it somehow. Unfortunately, JExcelApi does not support password protected files, so I need to find an alternative way to protect it.
Regarding the "send" button: I was thinking about adding a simple password dialog, so that the user needs to type in a hard-coded password first before the intent is sent. I still haven't taken a look at this, though.
What worries me the most is the XLS file. Ideally, it should still be available on the SD card's root folder, but I realize that this may make things much harder than necessary. Using the app's private storage would be option because the file would be "invisible", but this can be easily beaten by using a rooted phone. I've taken a look around the Cipher class but I'm not sure how I could apply it to my case: the JExcelApi manages the opening and saving of files by itself and I can't use CipherOutputStream to save the file; I also need to be able to decrypt the file on a PC.
What should I do? Is there any way to encrypt the file in Android in a way that would make it possible to decrypt it on a PC? Should I find some other Excel APIs that support password protection (are there even any)?
About the security requirements: the content of the report is not critical and it wouldn't be a big deal if our clients got access to it (I mean, the content itself is displayed on screen!), but I'd like to make it annoying enough that our clients would cease to insist accessing the XLS file, if they ever tried to.
TL;DR: how do I encrypt any kind of file in Android?
I'm not very familiar with encryption on Android, but there's the Bouncycastle library that can be used for encrytion on Android. There might be some pitfalls, but apparently you can also use Android's own Cipher class for en-/decrypting using different algorithms.
If you want to share the encrypted data you'll have to have a shared key in order to let the recipient decrypt it.
Related
I would like to make video/audio/pdf files hidden inside Internal/External storage in Android. Our requirement is making the files visible only in our Android application but not any other apps like Es File Explorer and not even when connecting the device to Desktop/Laptop.
I have googled it a lot and found the following ways but with few disadvantages.
Creating folder/file with prefix "." - It has the disadvantages that we cannot prevent it to be visible in some File explorer apps with the option "Show hidden files" and we cannot prevent the files from getting displayed when connected to Desktop/Laptop.
Storing the files inside App specific folder - Storing large memory files in the path returned by android.Content.Context.getFilesDir() will lead to the poor performance of the device and most of the devices will not have large internal memory size.
How to overcome the disadvantages and make our application to meet the requirement ?
Well hiding files to user accessable storage is not recommend without encryption.
Youtube,Gaana, saavan, hotstar all these media related apps used to encrypt their data and stores in data location which is visible to users but they can't share or use in other ways as the data is encrypted.
You can use CipherOutputStream and CipherInputStream for encryption and decryption of file in android.
There are two ways through which you can achieve your goal
Download a file and encrypt it, when you want to play that file decry-pt it in a temporary file and play it which I not recommend as it can increase the chances of data grabbing.
if you want to play encrypted file on the fly (not decrypting it in a temp file) then you can use Libmedia library. It streams encrypted file on local host and play it from there
Original answer : https://stackoverflow.com/a/35426842/9565955
Your first proposed solution won't work since it would make files accessible to anyone.
Second solution is perfect if you have limited file sizes. In case of large memory files it is always better to store them in External storage. But this would make it publicly accessible. To prevent that you can encrypt the files and store them in external storage.
Some suggestions while doing so :
Randomise the filenames so won't be easy to guess.
Refer this for simple file encryption.
Do not use static key for encryption as it can be reverse
engineered. Use different key for every file.
Do not store the original key in db/shared preference. Store the
hash of it instead.
You can even hash the key n times and then store in db. This would
make procedure a bit slow but provides more security as one has to
know the exact value of n to get the original key.
For added security you can even consider using Android's KeyStore to
derive the IV.
I have use AES encryption to secure my data in sdcard.It work fine but take some time to decrypt mp3 file as file size is large.
when I checked file stored in other application like whats-app ,Facebook etc.. it is encrypted in different way.
Is there is any other option which I can apply to secure my files in sdcard. Please help me.
First, I will start my mentioning that you should evaluate files size and encryption/decryption time versus file importance. For example, we may want a 500mb file be only accessible by our application through Android, in which case we can set the required permissions. Because this file is not that important for us, we may decide not to encrypt it and encrypt the small and important files.
This said, I would suggest looking into faster/less reliable encryption schemes which will produce faster results. Following that you mentioned Facebook, you can look at Conceal, an open source framework developed by Facebook.
I am writing an app for my final year project, so it's more so for proof of concept so it doesn't have to be the best app in the world.
It is like a file locker app that you can add and remove files from the app and when they are stored they will be encrypted. There will be a login of some sort for the user to enter and be verified on a DB.
I am still a novice in android so I still have a way to go, but I am getting there!
I was thinking when the file (which could be a doc, pdf, jpg, video file etc) is added to the app it would be stored in the internal storage (from what I have read it seems to be the best place to store app related content) and a record of the name and file type would be added to the DB and also the encrypted file name. So when the user looks at the app they will see a thumbnail of the pic and the file name, kinda like the My Files app shows up files within a folder.
My question is it best not to store the file directly into the DB but just use the DB as a reference with the file details, if so how could this be done?
Also I was thinking that an AES 128bit encryption method would be best suited for this. I have tried a couple of encryption examples but have only been able to do this with a txt file, when i tried it with a jpg the app just sat there and did nothing. It showed the encrypted and decrypted jpg but this was not viewable.
Would anyone be able to suggest a good way of encrypting any file type that would suit for my app?
Any help would be greatly appreciated!
Cheers,
Owen
If you want to do this properly, here are a few tips:
Don't store files in the database, unless you know in advance that they're going to be really titchy. Store them somewhere else, with a reference to them in the database.
The best place for them if they're smallish is internal storage in the app's private file space. But if you want to be able to store encrypted arbitrary data then you'll need to hit external storage.
Don't store the decryption key!
Ideally, you should find a way not to write the file anywhere when you decrypt it. That might not be possible, though, if you need to open it in another application afterwards. If you write the encrypted files to external storage, you should at the very least write the decrypted version to internal storage where there's some operating system protection against other apps reading it. If you write the decrypted file to external storage, anything will be able to get at it.
AES with a 128-bit key will do you fine.
I have some audio files that my app is downloading, and due to the size of the files it would be nice if I could store them on the user's external storage. However I need them to remain private to my application. Is there any way to accomplish this?
Not literally.
You could encrypt them, but then you would have to handle the playing yourself, in order to decrypt them (or play some game like streaming them from a local "server" which decrypts them as it reads).
Realize also that even things within your .apk itself are accessible on most devices (you will need to use care in obfuscating the encryption key), and the contents of your app's private storage folder are readable on the multitude of rooted devices.
One simple suggestion would be to encrypt your file and then store it in external memory. This would keep the data safe and secured. Other application wont be able to access it. To accomplish this you need to convert the file into ByteStream. Then using encryption function encrypt it and store to external memory. Change the extension of your file to some user-defined extension like myExt and store all in certain folder. When you want to use those files in your application, decrypt it and use it. The encryption key will help you to securely protect data.
As per my knowledge this will prevent other application to access your information.
I want to save some files on SDCard which will be downloaded from net. The user should not be able to have direct access to it. I mean the file should be secure and it should not be transferred to other device and if its transferred then it should not be in readable format. Is there a particular directory on SDCard where these files can be saved and be secure too? Also this files should be automatically deleted on uninstall of the app. I guess there is a direct way of that in Android 2.2 but not below that. So, if someone has any idea of doing that then please let me know.
Encryption. If you're concerned about the user reading a file that's the closest answer you'll find -- but you need a secure way to store the decryption key also, which is not really attainable.
Realistically, anything that must not be viewed by the device owner must not be on the device.
If the files are in the physical possession of a dedicated user there is no practical way to make them impossible to copy. You can make them DIFFICULT to copy, but not impossible.
If you use encryption as #mah pointed out, and then don't store the key on the device: fetch the key from a server, retain it in memory and never write out the decrypted file or the key to disk you might be ok in deterring the casual pirate. The dedicated souls will figure it out.