I'm an embedded engineer (not a network guru) building a piece of Linux-based equipment (a portable measurement instrument) that is normally not connected to the Internet, but we need to make it possible for the equipment to "call home" for support, including updates and troubleshooting, in a manner that compromises neither the product's security, nor the customer's network security nor our own company network.
The "call home" capability will be completely controlled by the user, perhaps by pressing a physical button to activate it, after the equipment has been connected to whatever network the customer chooses to use. For prototype and demonstrations systems, this network could be at someone's home or office or even via a phone connection (the equipment will contain only a wired Ethernet port, and the customer would need to provide a wired AP if WiFi access is desired).
Making the connection should require no per-call configuration at the user's end, nor within our box, so I'm thinking we can require the customer to provide DHCP, and not much else. We can also require the customer to first contact us before pressing the "call home" button, so we can have our support interface up only when needed.
When a unit does "call home", it merely makes a connection to a company system, doing nothing else until an engineer (well, me) directly connects to it. Other than the existence of the connection, we should get no (or minimal) information about the network the customer is using. So I'm thinking some kind of SSH connection, but that's as far as I have gotten.
If possible, it should "feel" as if I'm connecting locally, as if the unit were on my desk (perhaps with much more latency, loss, and minimal bandwidth).
But I have no idea whatsoever how to make an SSH connection (if that's the right tool to use for this) as two separate halves: The remote unit "calls" somewhere, presumably on one of our company systems, then that system notifies an engineer (me) that a "call home" has been initiated, then waits for the engineer to connect, forming the other half of the connection.
The connection need not identify the remote system (make, model, serial number, version, etc.): I'd do that manually after logging in securely.
If needed, I can create a new system on our end (Linux, BSD, Windows, whatever, physical or VM) that can be dedicated to just this function. I can get at least one static port mapped out to our corporate WAN, if needed (but something I'd prefer to avoid, if possible).
Ideally, I'd also like for there to be minimal information in the equipment itself, so that possession of the equipment by an adversary (or competitor) could not compromise customer or company networks, other units, nor the call-home technique itself. From what little I know, I'd guess a hostname or IP address, a port number, and a key would be needed, but less would be better!
I'd also like the system to require manual intervention at both ends, with minimal automation that can be buggy or be compromised. Once we implement and test the initial system, automation could be added as our experience with it, and confidence in it, grows.
That's about as far as my thinking has taken me. Beyond this, I'm pretty much clueless. Am I on the right track? What pieces am I missing? Is this already a popular thing to do, and I simply don't know what it is called? How simple and stupid can this capability be made for a couple of prototype systems?
EDIT: If it wasn't obvious already, please assume I'm a networking idiot who can be trusted only to follow an explicit recipe, and not much more. KISS applies!
Disclaimer: as long as no "real" answer is there I just provide my more or less theoretical thoughts with hope it helps.
Without reading in detail, I found http://www.vdomck.org/2005/11/reversing-ssh-connection.html to reverse a ssh-connection. If that is easy to follow (it should be easy, just ssh -R basically, see also http://www.brandonhutchinson.com/ssh_tunnelling.html) it means your remote device could connect to your network (and "Pete" is your Partner at the customer). The problem is that initiating a ssh-connection without user/password requires a authentication- private key on that device (so in non-friendly hands).
You could place a dumb ssh-server with no private data and no special access and even the password you could set just for that single connection (and tell your partner "Pete" via phone), let your phantasie play a bit to get a static half "ImGenious$%" and a dynamic half "1243" so you can give a short easy dynamic half over phone.
Then from that dumb ssh-server you can connect to your device as in the article.
I would suggest the call home functionality uses SSH to connect to your office. This requires your customer's network provides DHCP, Internet access and DNS capability. It also requires them to allow outbound connections on port 22. The latter is possibly an issue for some security minded customers who want to prevent unknown egress of data.
You will need a certificate for your SSH server so the certificate is valid for the domain name you choose. You will also need to make sure the SSH client on the server is configured to accept the signature of your server.
It sounds like the number of devices you will be maintaining is relatively low. For this reason, I would suggest generating unique public/private key pairs for each device. You can then load the public key into your server so logins are accepted via keys only.
If a device is compromised or stolen, you can delete the appropriate key from your server. The device will not be able to login again. The private key on the device only has value because you have decided to accept the associated public key on login. Remove this and it has no value. The added benefit is that you can identify a device by the key it has used to login (e.g. you can associate each key with a different user). You can then tie up the login with the information about the device/customer that you store on your systems.
If you use reverse SSH you can have the device connect in. Once you're ready, you can use the reverse part to connect through the tunnel that the device and your server have already setup to perform the maintenance.
Related
I do not trust anything, so I want to write my own firewall. I'm not satisfied with the application firewalls in Linux and Windows and the distro firewalls are not adequate for my purposes. I'm frustrated with distro firewalls, most of them like pfSense, OPN Sense, ipfire just seem to give illusion of firewall but all they do is packet filtering. I'm unable to block everything and only allow few websites with it, I have created a rule to block DNS requests, applied that rule and rebooted the firewall distro but it doesn't seem to have any effect. I either have to block everything or allow everything, both of which are undesirable. The sc*mbags seemed to have deliberately made the interface unintuitive to sell service, they claim their firewalls are free but made the interface obtuse, so that they can steal money by selling service.
I'm thinking of writing my own firewall, one of this will be an application which will run on the client system and the other would be standalone distro, both will run together to allow better management. The application on the client will create a special packet signed with the hash of the application, OS, etc and the intermediary firewall distro will check this hash and allow rules and policies to be created based on this hash. Does the TCP/IP protocol allow this?
I have searched the net for resources about network API on Linux, and there are three resources about writing my own firewall, two are questions here and one is netfilter. I don't know anything about TCP/IP protocol, so I don't know if I can use the packets made TCP/IP to achieve this or I have to creatively find a way to create a special packet.
I am trying to identify computers with a unique code based on their machine. However, I can't find any way to do this. I've tried to use mac addresses, but you can only the server's mac address when you're using a linux server. I would use the clients ip address, but it can change if they're using a proxy or vpn, or even if they just unplug their router for a bit.
Can anyone recommend something that would be good for this?
Thanks.
There is no secure way to uniquely identify computers based on hardware, and why should you?
The better practice would be to use an artificial key.
If you want to identify a person - you give it an ID (passport, driving license...), do the same here:
Use the session (apache generates automatically a session ID), or generate a UUID (there are many ways to do this). Or if you need to go beyond - use ssh key pairs, save them somewhere on the PC.
Now to the problem:
1. A client could lie about his hardware, his mac address, VIN/PID, serial number of the SATA cable. You can (and must) never trust such info!
2. Clients hardware could change, and then?
I suspect we're all familiar with how facebook and google and the like detect if you're using a different device than usual, I was wondering what the most reliable way to do this is?
I'm talking about the old 'It looks like you're signing in from a different device', and then when you confirm etc, it usually sends you an email and asks whether you want to trust this device or not.
Obviously one could just set a cookie, one that maybe get's checked and logged each visit, but what about when the user signs out? Do we keep the cookie?
Is there any other reliable method to 'trust' a 'device' other than setting cookies? Or is this the best/most reliable way to do it?
The most reliable way to detect a device change is to create a fingerprint of the browser/device the browser is running on. This is a complex topic to get 100% right, and there are commercial offerings that are pretty darn good but not flawless. I worked at one of those companies several years ago.
There is now at least one open source fingerprinting project Client JS. I have not used it, but it seems to cover the bases.
Just setting a cookie is not very reliable because on average users clear cookies about every 30-45 days unless you use a network that attempts to re-set the cookie (paid services). Even those are not flawless.
Just using the IP address is useless. Some devices legitimately have many IPs in a short period of time (laptop at home, work and Starbucks or most any mobile device), while sometimes a single IP is shared by a large number of users (all the folks at Starbucks or behind a corporate proxy server).
UPDATE
Thoughts on your similar hash code.
It is a complex topic to get right. I had a small team for a few years. We got pretty darn good, but you can never be 100% accurate even when people are not intentionally trying to trick you.
If the CPU changes, it's probably a different device.
The same physical device can have many user agents. Each browser on the device has a different user agent, and privacy mode of browsers have different user agents with far less entropy.
Fonts doesn't change very quickly for a given physical device, though it's not a great source of entropy on mobile devices (few fonts installed, and typically all the same ones for a given type of device).
OS is generally stable, until it suddenly changes. Does it matter in your case if every device appears to be a new device when it updates to Windows 10?
Color depth will be pretty stable. If the user installs a new graphic card, this may change. Does that matter in your case?
If you can accept thinking some devices are new when in fact they are the same and vice-versa, this type of similarity hash may work for you. Note that you can never use this type of fingerprint to uniquely identify a device for a purpose that requires positive identification such as access to secure data. It's great for making probabilistic decisions such as serving an appropriate ad.
Need a basic direction in the following project.
There is a linux based controller doing some industrial control stuff.
The box is equipped with cellular modem and is capable to get online through cellular carrier. Cellular communication is used because controller is mostly installed where no cables or short range radio is available. Places where sun don't normally shine :)
The task is to allow internet clients to connect directly to the box for some basic control/monitoring stuff. The problem is connectivity - how clients will discover the box? - I'd like to have the box act as a server (if possible). Assuming that cellular carrier allows the box to get online doesn't necessarily mean that the box will get public IP so that anyone would be able to get connected. To my understanding the cellular network acts as a gateway from those who are working inside of it, and reaching someone in that network from outside isn't possible. Am I wrong? We are looking for a generic solution, not a solution around particular cellular provider. The controller is installed in different countries, we need to find the standard way to "webify" it.
The software (and hardware) in the box is ours, we can basically do anything, but I am looking for the right way to do it in order to avoid surprises with different providers later. BTW, the solution doesn't necessarily have to be technical, may be it's possible to buy a permanent IP's per box, or setup VPNs.. Which way should I dig to? What questions to ask?
Your ideas are welcome!
Your summary of the problem is basically correct. I've implemented several systems that do this, and the odds of success are good.
The way you tackle this will depend on the number of remote units you expect a single user to interact with. If each user will handle only one or two devices, it's plausible to implement the web server on the remote device. If each user handles many devices, consider centralising as much administration as possible. I've implemented this using Zenoss for data logging, and a custom control server.
If the web server sits on the remote device, you can either buy a SIM with a static IP, or use a proxy server. I recommend setting up a proxy server unless the number of devices is very small.
There are three options for SIMs:
Static IP with an address on the public Internet will be expensive, and negotiating the deal with each provider in each country will be irksome. No proxy server is required.
Private APN SIMs will give you the option of a static address, but in a private address range. Negotiation with the mobile network is still required, and you will require a proxy server to sit between the public Internet and the private address range,
Standard data SIMs will connect to the Internet through NAT. You can use these to host your service by opening a VPN connection (we used openvpn) to your server. You can now reach the devices directly by connecting to the same VPN, or through a proxy server.
If you use openvpn, here are some more tips:
Give each unit a public serial number, and a private key. Store these in the firmware of the unit, and in a central database. Put the public serial number on the outside of the unit. You can use an openvpn login script to ensure that a particular unit always appears at the correct IP address, which keeps the proxy configuration static.
You can control openvpn's bandwidth usage by adjusting its keepalive behaviour, and how often it renegotiates. Measure and tune this before a large deployment.
The NAT timeouts in the mobile networks are generally between 5 and 15 minutes. The device must send a packet to the server often enough to keep NAT alive.
Cheap SIM deals may be web only with limited ports.
Other tips:
GPRS modem firmware can (rarely) crash internally. If your hardware supports it, provide software with the ability to power cycle the modem.
Test your box in areas with poor coverage in your own country before you send out international shipments.
This is a typical problem with "mobile agent" appearing in different places or using different providers (in this case just one provider, but it's almost the same). Usually it's solved using some kind of home agent - a server that the mobile connects to and gives details about how to reach it or if it can't be reached directly then the home agent acts as a proxy.
Client always contact the home agent first and then if it is possible they contact the mobile or if it's not they use the server as a proxy.
In some cases dynamic dns might be sufficient in other you need real proxy/ façade.
There's a good book: Andrew S. Tanenbaum & Maarten van Steen :"Distributed Systems: Principles and Paradigms"
You can ask cellular provider to give you a SIM card with internet access and fixed IP address. Then you can host any server you like. Do not forget that you are dealing with limited bandwidth.
I have a new set up for software development for iOS devices. I am using MACs for the development and the company may grow from three employees right now to 20 in near future. I want to make the MACs secure so that the client code is safe and does not leave office.
Few ways I can think of a notorious employee trying to do that is
Get it on USB-key/External-Disk
Burn it on CD/DVD
Transfer it to a bluetooth device
Transfer it to Infra-Red Device
Email it as an attachment
Upload it to Dropbox or any such service
FTP to a remote server
To handle this one by one I need to do following
Disable USB access to user accounts (only admin allowed to insert a new device). But often times we need to stick in iphone/ipod touch to do on-device testing. How can I restrict the devices or get notified when someone tried to put a foreign device in any of the USB slots?
Disable CD/DVD write functions except for admin. Can I do this?
Disable bluetooth access. And if someone tries to pair a device, can I get notified or maitain a log?
Wireless keyboard and mouse use Infra-Red (IR) technology. How can I limit these devices?
Need to block all outgoing emails except company emails. Can I keep a tab on all outgoing traffic (may be by file size) so that I know some one is trying to up-load a file?
Again disable access to such website. But then every 15 days a new service springs up. How do I tackle this?
Disable ftp outgoing services. Can I do this?
Importantly is there a monitoring software that will allow me to do this? I don't mind paying. But since this is a start-up I cannot spend a fortune on this. And of-course I prefer open source solutions for the control it gives me to extend and scratch my specialized itch :)
Finally I hope I wont be judged as a bad boss or something. I am all for developer freedom but we are into consulting business and protecting client code takes priority.
Thanks for your time and looking forward to your help.
Dev.
If you don't trust your developer not to run off with your source code, don't hire them. They can find a way around your "solution"
If you can't trust any developers to not steal your source code, work alone. Anything known by two people is no longer a secret.