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The NSA Warns of TLS Inspection

The NSA has released a security advisory warning of the dangers of TLS inspection:

Transport Layer Security Inspection (TLSI), also known as TLS break and inspect, is a security process that allows enterprises to decrypt traffic, inspect the decrypted content for threats, and then re-encrypt the traffic before it enters or leaves the network. Introducing this capability into an enterprise enhances visibility within boundary security products, but introduces new risks. These risks, while not inconsequential, do have mitigations.

[…]

The primary risk involved with TLSI’s embedded CA is the potential abuse of the CA to issue unauthorized certificates trusted by the TLS clients. Abuse of a trusted CA can allow an adversary to sign malicious code to bypass host IDS/IPSs or to deploy malicious services that impersonate legitimate enterprise services to the hosts.

[…]

A further risk of introducing TLSI is that an adversary can focus their exploitation efforts on a single device where potential traffic of interest is decrypted, rather than try to exploit each location where the data is stored.Setting a policy to enforce that traffic is decrypted and inspected only as authorized, and ensuring that decrypted traffic is contained in an out-of-band, isolated segment of the network prevents unauthorized access to the decrypted traffic.

[…]

To minimize the risks described above, breaking and inspecting TLS traffic should only be conducted once within the enterprise network. Redundant TLSI, wherein a client-server traffic flow is decrypted, inspected, and re-encrypted by one forward proxy and is then forwarded to a second forward proxy for more of the same,should not be performed.Inspecting multiple times can greatly complicate diagnosing network issues with TLS traffic. Also, multi-inspection further obscures certificates when trying to ascertain whether a server should be trusted. In this case, the “outermost” proxy makes the decisions on what server certificates or CAs should be trusted and is the only location where certificate pinning can be performed.Finally, a single TLSI implementation is sufficient for detecting encrypted traffic threats; additional TLSI will have access to the same traffic. If the first TLSI implementation detected a threat, killed the session, and dropped the traffic, then additional TLSI implementations would be rendered useless since they would not even receive the dropped traffic for further inspection. Redundant TLSI increases the risk surface, provides additional opportunities for adversaries to gain unauthorized access to decrypted traffic, and offers no additional benefits.

Nothing surprising or novel. No operational information about who might be implementing these attacks. No classified information revealed.

News article.

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Russians Hack FBI Comms System

Yahoo News reported that the Russians have successfully targeted an FBI communications system:

American officials discovered that the Russians had dramatically improved their ability to decrypt certain types of secure communications and had successfully tracked devices used by elite FBI surveillance teams. Officials also feared that the Russians may have devised other ways to monitor U.S. intelligence communications, including hacking into computers not connected to the internet. Senior FBI and CIA officials briefed congressional leaders on these issues as part of a wide-ranging examination on Capitol Hill of U.S. counterintelligence vulnerabilities.

These compromises, the full gravity of which became clear to U.S. officials in 2012, gave Russian spies in American cities including Washington, New York and San Francisco key insights into the location of undercover FBI surveillance teams, and likely the actual substance of FBI communications, according to former officials. They provided the Russians opportunities to potentially shake off FBI surveillance and communicate with sensitive human sources, check on remote recording devices and even gather intelligence on their FBI pursuers, the former officials said.

It’s unclear whether the Russians were able to recover encrypted data or just perform traffic analysis. The Yahoo story implies the former; the NBC News story says otherwise. It’s hard to tell if the reporters truly understand the difference. We do know, from research Matt Blaze and others did almost ten years ago, that at least one FBI radio system was horribly insecure in practice — but not in a way that breaks the encryption. Its poor design just encourages users to turn off the encryption.

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Detecting Drone Surveillance with Traffic Analysis

This is clever:

Researchers at Ben Gurion University in Beer Sheva, Israel have built a proof-of-concept system for counter-surveillance against spy drones that demonstrates a clever, if not exactly simple, way to determine whether a certain person or object is under aerial surveillance. They first generate a recognizable pattern on whatever subject­ — a window, say — someone might want to guard from potential surveillance. Then they remotely intercept a drone’s radio signals to look for that pattern in the streaming video the drone sends back to its operator. If they spot it, they can determine that the drone is looking at their subject.

In other words, they can see what the drone sees, pulling out their recognizable pattern from the radio signal, even without breaking the drone’s encrypted video.

The details have to do with the way drone video is compressed:

The researchers’ technique takes advantage of an efficiency feature streaming video has used for years, known as “delta frames.” Instead of encoding video as a series of raw images, it’s compressed into a series of changes from the previous image in the video. That means when a streaming video shows a still object, it transmits fewer bytes of data than when it shows one that moves or changes color.

That compression feature can reveal key information about the content of the video to someone who’s intercepting the streaming data, security researchers have shown in recent research, even when the data is encrypted.

Research paper and video.

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More on the NSA’s Use of Traffic Shaping

“Traffic shaping” — the practice of tricking data to flow through a particular route on the Internet so it can be more easily surveiled — is an NSA technique that has gotten much less attention than it deserves. It’s a powerful technique that allows an eavesdropper to get access to communications channels it would otherwise not be able to monitor.

There’s a new paper on this technique:

This report describes a novel and more disturbing set of risks. As a technical matter, the NSA does not have to wait for domestic communications to naturally turn up abroad. In fact, the agency has technical methods that can be used to deliberately reroute Internet communications. The NSA uses the term “traffic shaping” to describe any technical means the deliberately reroutes Internet traffic to a location that is better suited, operationally, to surveillance. Since it is hard to intercept Yemen’s international communications from inside Yemen itself, the agency might try to “shape” the traffic so that it passes through communications cables located on friendlier territory. Think of it as diverting part of a river to a location from which it is easier (or more legal) to catch fish.

The NSA has clandestine means of diverting portions of the river of Internet traffic that travels on global communications cables.

Could the NSA use traffic shaping to redirect domestic Internet traffic — ­emails and chat messages sent between Americans, say­ — to foreign soil, where its surveillance can be conducted beyond the purview of Congress and the courts? It is impossible to categorically answer this question, due to the classified nature of many national-security surveillance programs, regulations and even of the legal decisions made by the surveillance courts. Nevertheless, this report explores a legal, technical, and operational landscape that suggests that traffic shaping could be exploited to sidestep legal restrictions imposed by Congress and the surveillance courts.

News article. NSA document detailing the technique with Yemen.

This work builds on previous research that I blogged about here.

The fundamental vulnerability is that routing information isn’t authenticated.

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