Beware Using Internal Encryption as an IT Security Blanket

It certainly sounds reasonable: networks are moving toward a perimeter-less model so the line between internal and external network is blurring. The introduction of cloud computing as overdraft protection (cloud-bursting) further blurs that perimeter such that it’s more a suggestion than a rule. That makes the idea of encrypting everything whether it’s on the internal or external network seem to be a reasonable one.

Or does it?


A recent post posits that PCI Standard or Not, Encrypting Internal Network Traffic is a Good Thing. The arguments are valid, but there is a catch (there’s always a catch). Consider this nugget from the article:

Bottom line is everyone with confidential data to protect should enable encryption on all internal networks with access to that data. In addition, layer 2 security features should be enabled on the access switches carrying said data. Be sure to unencrypt your data streams before sending them to IPS, DLP, and other deep packet inspection devices. This is easy to say but in many cases harder to implement in practice. If you run into any issues feel free to post them here.

I realize this is a controversial topic for security geeks (like myself) but given recent PCI breaches that took advantage of the above weaknesses, I have to error on the side of security. Sure more security doesn’t always mean better security, but smarter security always equals better security, which I believe is the case here. [emphasis added]

It is the reminder to decrypt data streams before sending them to IPS, DLP, and other “deep packet inspection devices” that brings to light one of the issues with such a decision: complexity of operations and management.

It isn’t just the additional latency inherent in the decryption of secured data streams required for a large number of the devices in an architecture to perform their tasks that’s the problem, though that is certainly a concern. The larger problem is the operational inefficiency that comes from the decryption of secured data at multiple points in the architecture.

See there’s this little thing called “keys” that have to be shared with every device in the data center that will decrypt data, and that means managing each of those key stores in their own right. Keys are the, well, key to the kingdom of data encryption and if they are lost or stolen it can be disastrous to the security of all affected systems and applications. By better securing data in flight through encryption of all data on the internal network an additional layer of insecurity is introduced that must be managed.

But let’s pretend this additional security issue doesn’t exist, that all systems on which these keys are stored are secure (ha!). Operations must still (a) configure every inline device to decrypt and re-encrypt the data stream and (b) manage the keys/certificates on every inline device. That’s in addition to managing the keys/certificates on every endpoint for which data is destined. There’s also the possibility that intermediate devices for which data will be decrypted before receiving – often implemented using spanned/mirrored ports on a switch/router – will require a re-architecting of the network in order to implement such an architecture.

Not only must each device be configured to decrypt and re-encrypt data streams, it must be configured to do so for every application that utilizes encryption on the internal network. For an organization with only one or two applications this might not be so onerous a task, but for organizations that may be using multiple applications, domains, and thus keys/certificates, the task of deploying all those keys/certificates and configuring each device and then managing them through the application lifecycle can certainly be a time-consuming process. This isn’t a linear mathematics problem, it’s exponential. For every key or certificate added the cost of managing that information increases by the number of devices that must be in possession of that key/certificate.


The real problem, as evinced by recent breaches of payment card processing vendors like Heartland Systems is not that data was or was not encrypted on the internal network, but that the systems through which that data was flowing were not secured. Attackers gained access through the systems, the ones we are pretending are secure for the sake of argument. Obviously, pretending they are secure is not a wise course of action. One cannot capture and sniff out unsecured data on an internal network without first being on the internal network.

This is a very important point so let me say it again: One cannot capture and sniff out unsecured data on an internal network without first being on the internal network.

It would seem, then, that the larger issue here is the security of the systems and devices through which sensitive data must travel and that encryption is really just a means of last resort for data traversing the internal network.

Internal encryption is often a band-aid which often merely covers up the real problem of insecure systems and poorly implemented security policies. Granted, in many industries internal encryption is a requirement and must be utilized, but those industries also accept and grant IT the understanding that costs will be higher in order to implement such an architecture. The additional costs are built into the business model already. That’s not necessarily true for most organizations where operational efficiency is now just as high a priority as any other IT initiative.

The implementation of encryption on internal networks can also lead to a false sense of security. It is important to remember that encrypted tainted data is still tainted data; it is merely hidden from security systems which are passive in nature unless the network is architected (or re-architected) such that the data is decrypted before being channeled through the solutions. Encryption hides data from prying eyes, it does nothing to ensure the legitimacy of the data. Simply initiating a policy of “all data on all networks must be secured via encryption” does not make an organization more secure and in fact it may lead to a less secure organization as it becomes more difficult and costly to implement security solutions designed to dig deeper into the data and ensure it is legitimate traffic free of taint or malicious intent.

Bottom line is everyone with confidential data to protect should enable encryption on all internal networks with access to that data.

The “bottom line” is everyone with confidential data to protect – which is just about every IT organization out there – needs to understand the ramifications of enabling encryption across the internal network both technically and from a cost/management perspective.

Encryption of data on internal networks is not a bad thing to do at all but it is also not a panacea. The benefits of implementing internal encryption need to be weighed against the costs and balanced with risk and not simply tossed blithely over the network like a security blanket.


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Published May 28, 2009
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