It seems like there are lots of ways to prevent man in the middle attacks. I've read many on here and on the rest of the internet. According to wiki you need a secure channel as well to completely safeguard against it. I have two questions in regards to preventing it in the real world.

Does the US government monitor 100% of the lines dug in the US? Obviously (hopefully) data centers are secured but what is there to stop someone from driving out into the desert and physically tapping into a line?

In that scenario, is there anything that can be done by two nodes to detect someone started eaves dropping? (Maybe more of a physics question?) Are there any protocols like this already?

This question is in the scope of public key cryptography because if you have a secure channel you can just exchange a new key as needed.

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    I would assume at the very least there is encryption protecting someone from just eavesdropping. Commented Oct 23, 2014 at 20:38
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    Perhaps Encryption used to be prohibitive in terms of time to decode and encode but no and days it's pretty fast and effective. Also, I don't think you understand how public key encryption works. It's not like there is just a public key that everyone knows. Commented Oct 24, 2014 at 1:37
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    Why would the US government monitor lines owned and operated by private corporations? And why would anyone monitor physical lines when the majority of internet traffic is sent over cell towers?
    – MCW
    Commented Oct 24, 2014 at 12:23
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    @Carlos, even in your case, a MiTM attack would only be able to read data it could decode (having the private key) or data that unencrypted. Regardless, you, yourself do not provide the end-to-end encryption. I assume (because I do not have a source on hand) that the ISP and all the other infrastructure also encrypts all the data they send... Thus, while nothing is technically stopping you from doing a MiTMa, you would only get a mass of encrypted data. Commented Oct 24, 2014 at 14:31
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    @MarkC.Wallace, Why would the US government monitor lines owned and operated by private corporations? I almost spilled my coffee ;) Commented Oct 24, 2014 at 14:32

6 Answers 6


Physical surveillance of millions of miles of buried cables would be preposterously expensive. The US government already fails at efficiently preventing illegal immigration across the Mexican/USA boundary, which is one or two orders of magnitude shorter than the total length of cables.

Instead, US government does things like everybody else: with encryption (or so we hope, at least). A good encrypted tunnel (e.g. SSL) keeps attackers at bay.

Encryption ensures confidentiality. A good tunnel also provides data integrity, in the following sense: alterations are reliably detected. However, if an attacker uses a shovel to get to the cable, he can cut it (it has happened). To make communications more resilient, one must use redundancy; see this answer (when the attacker wields nuclear weapons, you have to think big in terms of redundancy).

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    I would say they fail at protecting the border as a matter of priority, rather than a matter of ability ;-). (Who doesn't want cheap labor!?) But yes, your point is clearly valid. Its been a while since i've taken cryptography but i recall a method where you can figure out an encryption key by repeated analyzing different messages. (Consider analyzing twitter posts which are short and therefore predictable) Wouldn't a 'trunk' line be vulnerable to this attack? Commented Oct 24, 2014 at 1:07
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    @CarlosBribiescas Figuring out an encryption key by analyzing many messages is not a universal property of cryptographic algorithms. It is merely a property of some particularly poor algorithms, or more charitably to the algorithms, some poor implementations of algorithms. Good cryptography, properly implemented and used, does not have such a weakness. If it did, it would not be good cryptography.
    – Xander
    Commented Oct 24, 2014 at 1:43
  • @CarlosBribiescas Also, a trunk line will carry a huge number of packets to/from many points. Each may use different encryption algorithms with different keys/lengths. Other difficulties exist that make it difficult enough to place a successful tap. Commented Oct 24, 2014 at 10:35
  • Not to mention the time it would take to splice fiber and connect both ends to your tap properly. Even just repairing a broken fiber line takes hours. I doubt someone will have that time before authorities are on their asses.
    – user41341
    Commented Oct 24, 2014 at 16:52
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    @bluefish it's not necessary to splice them, there are passive fiber taps that will leave the cable intact. Commented Oct 24, 2014 at 17:04

There are a few countermeasures they typically deploy. One is encryption, which is pretty straightforward. They also monitor their fiber optics for unexpected attenuation or a change in the scattering of the light. Additionally there are ways to configure fiber to detect acoustical disturbances, theoretically detecting the tap being placed.

They also have a standard in place that has requirements revolving around the conduits, carriers, etc. for sensitive data. The standard is named NSTISSI 7003 and there are also some summaries out there if you'd like to know more. Additionally, they use the TEMPEST standard which discusses how to protect against electromagnetic radiation leaking which could theoretically be detected without physically breaching the conduit the cables are run through. TEMPEST also covers eavesdropping but the eavesdropping portion has not been released as far as I know.

  • Thomas' post looks at the overall picture (resiliency of the network) without bothering with nitty-gritty details, while yours directly answers the question. Commented Oct 25, 2014 at 20:43
  • Yeah, and thanks for directly addressing the physical aspect of the question thoroughly. Adding to my original question, do you know if they physically monitor(instead of protect) lines? In example, they could bury devices to monitor physical disturbances near the lines. That would be more practical. Commented Oct 25, 2014 at 21:00
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    Dark fiber can be used to detect acoustic vibrations which could detect somebody messing with the fiber. There may be other methods I'm unaware of. This way they only need to have people available to physically inspect where the disturbance occurred. Vendors in this space boast an ~10 meter resolution on detection, so you wouldn't have to travel miles to find it. Commented Oct 25, 2014 at 21:32
  • This is the correct answer. For some more examples of physical technologies and procedures used to monitor cables that carry protect high-security data over them see en.wikipedia.org/wiki/Protective_distribution_system. (Note that while a lot of the "bury everything in concrete"-type measures are outdated (for many use cases, anyway; probably not for the cable conduits that connect Minuteman missile silos) many links that are protected as such are still in use. To the consternation of many who have to send data/voice over the old, low-bandwidth connections. Commented Oct 23, 2015 at 20:59

Internet lines don't need to be secured. Encryption allows one to set up a secure channel within an insecure medium.

In short, no, the US does not monitor the physical lines because it doesn't need to. There is infrastructure monitoring, but that's not what you are asking about.


I used to be a sysadmin for the military; we were told that there were a (small) number of monitored connections between the military and public Internet -- the idea being that the military could cut itself off from the rest of the world but still maintain internal communications.
I wasn't important enough to be able to personally verify whether this was true, but that would be a simple and fairly effective layer of security. (I should also note that this was a number of years ago.)

I can't speak to the rest of the US government. But, as other respondents have noted, monitoring the entire cable plant would be prohibitively expensive.

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    I'm pretty sure this is actually true. Also, SIPRNet and JWICS are completely physically isolated from the internet, IIRC.
    – reirab
    Commented Oct 24, 2014 at 14:10

I think this has already happened in the past. Usual countermeasures are encryption secured by previously exchanged keys, monitoring of physical characteristics of a channel, and IDS. In the future quantum cryptography should solve this issue somewhat through the use of quantum entanglement. Oh, and most lines belong to private companies anyway...


If a single link existed, I would understand increased physical security to protect that link. However with the internet having been built on a mesh topology, traffic can take any number of routes to its destination. This gets to the point of prior posts noting it is not financially possible to physically protect all of those links.

While I've never been involved in government organizations, I'm sure they have "things" in place to monitor links (i.e. Health of the Internet). Detecting anything from up/down status to performance degradation. This would be more efficient way to monitor then to have a physical presence.

As others have pointed out, use of encryption makes MitM a mostly moot point. I say mostly because it depends on the encryption being used. Using encryption carries with it a significant level of latency which may or may not be acceptable for a particular use case. If latency is the primary driver one may elect for a less secure method of encryption. You mentioned the use of public key encryption. You're right that it is designed with a goal of placing traffic on an untrusted network by way of exchanging public keys. However asymmetric encryption is orders of magnitude slower than symmetric encryption so that would be a point of consideration.

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