encryption – EXPLOINSIGHTS, INC. Sys-Admin

So we’ve been asked ‘How do you share files from Nextcloud securely’?

It’s a fair question because if you END-TO-END encrypt a file, you can’t actually share the file unless you also share a means of decrypting it. And we don’t share our end-to-end encryption keys, EVER.

So how do we manage sharing? How do we protect our files as we hand them over to our customers? The short answer is with LAYERS of security:

Our files are protected by one of several levels of independent security:

Robust SSL/TLS connectivity (HTTPS all digital coms)

End-to-end encryption for files

Server-side encryption for files

Full Disk Encryption (FDE) for computer drives (server or desktop)

We can ignore FDE here as it doesn’t really come into play (it’s only really applicable here to a stolen PC).

For normal at-rest files, we have end-to-end AND server-side encryption in play. So our files are protected against threats of all kinds. You just can’t get at our data without TWO separate sets of credentials, neither of which are connected, neither of which are stored in a file.

When we share a file, we have to remove one of these layers (the end-to-end encryption), and that of course makes the protection weaker during the process of sharing FOR THAT FILE, since it only has server-side encryption to keep it safe. Note that this is not “bad” – the file is still encrypted, and it’s safe from even quite determined hackers. But you know, we like to be a bit paranoid and very responsible, so we bring other measures in play.

Firstly, here’s a real file from our server we created with end-to-end encryption still applied:

It’s very exciting. #notReally. You can see, the name is complete gibberish. And for the record, if you download this ‘blob’ and view it in Notepad, this is what you get:

“îe¤ÎÈCÀ’0pMi%?/£`ÕÕäÔ}CÇ+>ê3Ø½[Æ~©HïïþÑàß·”M*ÓÝì?L‚L*x)š!ýU\nW£7zšK‚ubÎ
91Ïií=¡l‰¸üN#åS›¬Æàçý*¨”PÔãºÕë*,8ƒÇŠûìÒ†Áè‹™p\\©Jšs|Ö_ž›”ÒÿEÊ ÈÈõÁÁ”

And as you will see later, the real file is actually a simple text message.

Once the file has end-to-end encryption removed, we can now more easily find it on the server AS THE SYS-ADMIN (or as a hacker that has somehow penetrated our system). It takes a while, but you can find it:

Wow, there it is. Plain as day. This file is actually present in an lxc container. If you can ‘see’ this, you are ither a SysAdmin or an unauthorized hacker. But the good news, you are not at the system root (you just think you are), so your damage potential is still very limited.

The file we created especially for this demo is shown among other directories. The server ADMIN or hacker (not necessarily the owner of the file) can “see” the file, so it seems. But before everyone panics, let’s take a close look at what he or she can actually “see”. There’s a file name and permissions and modification time and apparent size (meta-data if you will). You can also see file/folder names too. Gosh, does that mean the SYS-ADMIN or hacker can snoop on my files? Let’s look at the contents using cat:

Well that doesn’t look terribly useful. As you can see, the DATA are still encrypted. Albeit this time via the SERVER keys. A hacker and even the SysAdmin can’t look at file contents (but it’s true, he or she can see the name and other file meta data). So, the file is still quite well protected against hacking and theft.

In fact, the ONLY way you can view these data is if you unlock the server-side encryption that’s now in effect for that file. And for this, you either need an exploit that works against Nextcloud’s encryption (very unlikely) OR you need to somehow secure the credentials needed to login to the Nextcloud account which will then unlock these files. For that, you need a Nextcloud password AND 2FA code (one that changes every 30 seconds), so that too we think is quite safe from unauthorized disclosure. But when you do enter those data, the file becomes fully decrypted and is then more visible, albeit over an HTTPS connection only (our final level of protection):

So “finally”, this is a file we can read: HelloWorld.txt, that says “Hello everyone. Have a nice day”. So the Nextcloud user can read the file (just as he/she should).

When it comes to SHARING this file, we actually share an HTTPS:// link for that file that includes the decryption credentials for that file. In Nextcloud, this is what that looks like:

You can see on the bottom right that a sharing link has been created. We also add a PASSWORD to that link and an EXPIRATION DATE for the link, so that the link will not be active for long AND you need the extra password to access the file. We send the LINK to the file via regular email. Regular email is not terribly safe. It can be intercepted. We know that. But let’s continue:

This link looks like this:

https://cloudvault.exploinsights.com/index.php/s/aeX7irmbWfneipn

(The link won’t exist for long, so it’s probably not worth trying, sorry!).

If you click on the link and it’s still active, it will bring up THIS page:

Which is still not the file. You need that password. We do not send the password with the link. We don’t even send the password via email. We send that via another means, say WhatsApp, or Signal or even SMS. So, to get to this file, you need the link (from an email sent to you) AND the password (sent in a different way) sent to you. Finally, if you get the link and the password, you can click/enter the top secret password assigned to protect this file, you get rewarded in this case with this:

The file. In decrypted form. Finally! You can download the file but ONLY via https:// (SSL/TLS) connection (our final layer), so even then it remains encrypted-in-transit until it hits your download folder. Only then do we relinquish our management –> OVER TO YOU! 🙂

So that’s how we share our data. it is ALWAYS protected with up to four layers of encryption: FDE, End-to-End, Server-side and lastly SSL/TLS.

These “layers” are gradually stripped off as we get closer and closer to sharing a file with you, but only when it lands on your machine is our last (but strong) layer of encryption removed. We use 2FA credentials to share our data and even the Sys-Admin (or unauthorized hacker) has very little access to our data: they NEVER see raw decrypted data, but occasionally they can sometimes view a file name and some basic meta-data.

Is this perfect? No. We are always looking to improve it. This system is our latest and greatest implementation, but it won’t be our last. Is this pretty good? We think so! What do you think?

So this is how we ROLL our file-sharing; how we securely share data with our customer. What do you do?

Comments by email only – [email protected] or you can catch us on Twitter @SysAdminEI

So like all SysAdmins, we have a lot to worry about in order to continually meet the burdens of compliance. For us, data residency (location) and digital “state” (encryption status) is very important.

We have had a productive few days improving the PERFORMANCE of our systems by using better-integrated software. So, why is PERFORMANCE being addressed under compliance? Well, simply, because if you make a compliant system easier to use, users are more likely to use them, and thus be more compliant.

It’s no secret, we are great fans of Nextcloud – we self-host our cloud server, and because we use that to host our data, we use several different security layers to help thwart accidental and malicious exposure. Our cloud server, based at our office HQ in Tennessee, is where we store all of our important data. So we try to make it secure.

Firstly, our cloud server can only be accessed by HTTPS (SSL/TLS). Logging in requires 2FA credentials:

This gets you to the next step:

So this is good. And we have server-side encryption enabled in Nextcloud, which provides an additional layer of security – not even the SysAdmin can read the client data on the server.

This is cool. Server-side encryption does help us with sharing of files to customers, but because the decryption key is stored on the server, we don’t like to rely solely on that for protecting our important data.

So our data are end-to-end encrypted with Cryptomator – an open source, AES encryption software package, with apps for Linux, Windows and Android (we use all three) – and even apps for IOS for those that like their Apples too (we don’t).

Of course, one of the things that makes this system “inconvenient” is that it’s hard to access end-to-end cloud-encrypted files quickly. On the server, they look like THIS:

Not entirely useful. Really hard to work on a file like this. You have to physically download your encrypted file(s) (say using the webdav sync software platform, like the great one provided by Nextcloud) and store them locally on your device, then decrypt them locally, on your device, so you can work on them. This is fine when you are in your office, but what about when you are on the road (as we often are)?

Data residency and security issues can arise with this method of working when on travel, so you can’t download files en-mass to your device and decrypt them all when you are in the “wrong place”. You have to wait until you can get back to a right location before you can work. Customers don’t really like the delays this can cause them, and we don’t blame them. And worse still, in that situation, even when you are done, you have to delete (or even ERASE) files on your PC if you are going back on travel etc. again to a location where data residency becomes an issue. Then when you get to a secure location again, you have to repeat this entire process for working on your files again. This is hard to do. Believe us, we know, as we have had to do this, but we now have a better way.

A more secure but LESS CONVENIENT way is to somehow only download the files you need as you need them, and decrypt and work on them etc. ONLY AS YOU NEED THEM. This is more secure, as you only have one decrypted file on your device (the one you are working on in your word processor etc), but how can that be done and be done CONVENIENTLY?

Obviously, this “convenience v security” issue is one we have spent a lot of time looking at. We have used webdavs connected to our cloud servers and tried to selectively sync folder(s). It’s not efficient, not pretty, not fast (actually really slow) and sometimes it just doesn’t work.

But thankfully we now have a much faster, reliable, efficient, effective yet totally compliant way of addressing the problem of keeping files end-to-end encrypted yet still be able to work on them ONE AT A TIME even when you are in a location that can otherwise bring data residency issues.

For us, this requires several systems that have to work together, but they are built (mostly) on Open Source software that has, in some cases, been tried and tested for many years so is probably as good as you can get today:

OpenSSH – for Secure Shell connectivity;
Nextcloud server;
Nextcloud sync clients;
Cryptomator;
2FA Authentication credential management apps;
And last but not least…Mountain Duck.

SSH is an established, reliable secure service used globally to securely connect to servers. If configured correctly, they are very reliable. We believe ours are configured properly and hardened, not least because NONE of our SSH connections work with a username/password login. Every connection requires a strong public/private key combination, and every key itself is further password protected; and, each SSH connection ALSO requires a second-factor (2FA) code. We think that’s pretty good. We have already explained Nextcloud and Cryptomator. 2FA apps are the apps that generate the six-digit code that changes on your phone every 30 seconds. We have written about a new one we like (PIN protected), so we won’t go into that anymore. That leaves ‘Mountain Duck’. Yes ‘Mountain Duck‘. We know, it’s not a name one naturally gives to a secure file-access system, but bear with us (and in any case, we didn’t name it!). Put simply, Mountain duck allows us to use our 2FA protected SSH connections to our servers to access our files, but it does so in a really neat way:

In the image above, taken from their we site, note the text we circled in red. Mountain Duck comes with CRYPTOMATOR integration. So this effectively makes Mountain Duck a ‘Windows explorer’ that can be 2FA-connected via SSH to a server to access and decrypt in real-time Cryptomator end-to-end encrypted files stored on our HQ-based servers. To that, we say:

Just WOW.

So how does this work in the real world; how do we use this?

Well we have a Nextcloud sync client that syncs each users files to a separate LXC container running on the corporate server. Each container is used to sync the users files between the Nextcloud server and the Nextcloud user files. Both the Nextcloud server AND the Nextcloud client files are ultimately stored in the HQ facilities, albeit in very different LXC containers. Files are end-to-end encrypted in both the Nextcloud server and the Nextcloud client container. All are further protected by full disk encryption and SSL/TLS connectivity.

Whether we are on the road OR in the office, we work on our files by logging into our Nextcloud client container using OpenSSH and Mountain Duck.

It’s all a lot simpler than it might sound: First, we connect to our Nextcloud client containers via strong SSH credentials via Mountain Duck’s friendly interface, which asks first for our private key password:

And then asks for our 2FA code:

The 2FA code is generated on an our 2FA App on our encrypted, locked android smartphone, in a PIN protected app (We use ‘Protectimus‘ and also ‘andOTP‘).

With these credentials, Mountain Duck logs into our Nextcloud client container via the secure SSH connection, and then it accesses our end-to-end encrypted files but in doing so, it automatically detects our Cryptomator Vault (because it’s built into Mountain Duck) And it then allows us (if we want) to UNLOCK our Cryptomator Vault and access it:

So in one operation and three “codes”, we can securely connect to our Nextcloud client container via secure SSH and access our end-to-end encrypted files from anywhere in the world (where there’s internet!).

And Mountain Duck makes this easier because it allows you to bookmark the connection: open Mountain Duck and click a bookmark to the SSH server then enter your SSH password/2FA code. Mountain Duck logs into your server and accesses the files located there. It can even remember your passwords if you want (we don’t do that, as we don’t trust Windows much at all), but you could configure this to JUST require a 2FA code if you want.

The whole process takes, maybe, 30 seconds including the time to get the phone out and obtain a 2FA code. Not bad! And once you have done that, you can work on your END TO END encrypted files stored on your office based Nextcloud client container files from anywhere in the world. No files are needed to be on your PC – in the office or on the road. Everything remains solidly encrypted so if you do get hacked, there are no readable data that can be stolen, so at least that threat is low. And everything is going through modern, secure OpenSSH transfer protocols, which in our case, makes us sleep a lot better than having some proprietary code with back-doors and all sorts of unpleasant surprises that always seem to arise.

The catch? Well, you do need internet connectivity or you can do NOTHING on your data. The risk in the office is low, but when your on the road it does happen, so it’s still not perfect. 🙂

Also, you do have to set this stuff up with some poor SysAdmin. But if we can do it, probably anyone can?

Finally, this is what it looks like for real after we go through that hard-to-explain-but-easy-to-do login. A window appears and you can see your files just like a normal file view on your Windows PC.

Above is a regular Windows Explorer window, accessing the Nextcloud client container files via fast and secure SSH. The folder ‘Vault’ is actually a Cryptomator end-to-end encrypted folder, but because we have entered the credentials (above), it can be accessed like any other. Files inside can be copied, edited, saved, shared, printed etc. just as files in the other folders. It’s totally transparent, and it’s TOTALLY AWESOME. The files in the Nextcloud client container (and the Nextcloud server) remain fully encrypted all the time. A file ONLY gets decrypted when it’s selected and downloaded by the user. Viewing a file in explorer (as in the view above) does NOT decrypt it – you have to double-click etc. the file to initiate downloading and decryption. All your changes get immediately sync’d to the Nextcloud client container (which immediately sync’s everything back to the server). Nothing gets stored on the PC you are using to work on your files unless you deliberately save it to the device.

So, THIS is how WE roll our own end-to-end encrypted data storage. How do you do yours?

questions or comments by email only [email protected]

Tag: encryption

Securely Sharing Files from Nextcloud

Meeting Compliance with the aid of Nextcloud, Cryptomator and Mountain Duck