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Physical Key Extraction Attacks on PCs

Physical Key Extraction Attacks on PCs, illustration

Credit: Iwona Usakiewicz / Andrij Borys Associates

Cryptography is ubiquitous. Secure websites and financial, personal communication, corporate, and national secrets all depend on cryptographic algorithms operating correctly. Builders of cryptographic systems have learned (often the hard way) to devise algorithms and protocols with sound theoretical analysis, write software that implements them correctly, and robustly integrate them with the surrounding applications. Consequentially, direct attacks against state-of-the-art cryptographic software are getting increasingly difficult.

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Key Insights


For attackers, ramming the gates of cryptography is not the only option. They can instead undermine the fortification by violating basic assumptions made by the cryptographic software. One such assumption is software can control its outputs. Our programming courses explain that programs produce their outputs through designated interfaces (whether print, write, send, or mmap); so, to keep a secret, the software just needs to never output it or anything that may reveal it. (The operating system may be misused to allow someone else's process to peek into the program's memory or files, though we are getting better at avoiding such attacks, too.)


Robert Okajima

The following letter was published in the Letters to the Editor in the August 2016 CACM (
--CACM Administrator

Highly classified information on personal computers in the U.S. today is largely protected from the attacks Daniel Genkin et al. described in their article "Physical Key Extraction Attacks on PCs" (June 2016). Here, I outline cost-effective defenses that will in the future completely defeat such attacks, while making even stronger cyberattacks extremely difficult.

For example, tiny Faraday cages can be constructed in a processor package so encryption/decryption can be performed without the possibility of inadvertent emanations that could be measured or exploited, because all external communication to a cage would be through optical fiber and the cage's power supply is filtered.(1) This way, encryption keys and encryption/decryption processes would be completely protected against the attacks described in the article. In such a Faraday cage, advanced cryptography (such as Learning With Errors) could not be feasibly attacked through any known method, including quantum computing.

Hardware can likewise help protect software, including operating systems and applications, through RAM-processor package encryption. All traffic between a processor package and RAM can be encrypted using a Faraday cage to protect a potentially targeted app (which is technically a process) from operating systems and hypervisors, other apps, and other equipment, including baseband processors, disk controllers, and USB controllers. Even a cyberattack that compromises an entire operating system or hypervisor would permit only denial of service to its applications and not give access to any application or related data storage. Similarly, every-word-tagged extensions of ARM and X86 processors can be used to protect each Linux kernel object and each Java object in an app from other such objects by using a tag on each word of memory that controls how memory can be used. Tagged memory can make it much more difficult for a cyberattacker to find and exploit software vulnerabilities because compromising a Linux kernel object or a Java application object does not automatically give power over any other object. Security-access operations by such objects can be strengthened through "inconsistency robustness" providing technology for valid formal inference on inconsistent information.(1) Such inconsistency robust inference is important because security-access decisions are often made on the basis of conflicting and inconsistent information.

Such individual processor-package cyberdefense methods and technologies will make it possible, within, say, the next five years, to construct a highly secure board with more than 1,000 general-purpose coherent cores, greatly diminishing dependence on datacenters and thereby decreasing centralized points of vulnerability.(1)

These technologies promise to provide a comprehensive advantage over cyberattacks. The U.S., among all countries, has the most to lose through its current cyberdefense vulnerabilities. In light of its charter to defend the nation and its own multitudinous cyberdefense vulnerabilities, the Department of Defense is the logical agency to initiate an urgent program to develop and deploy strong cyberdefenses using these technologies and methods. Industry and other government agencies should then quickly incorporate them into their own operations.

Carl Hewitt
Palo Alto, CA



We agree that high-security designs can mitigate physical side channels. However, they are typically difficult to design, expensive to manufacture, reduce performance, and are unavailable in most commercial and consumer contexts. Moreover, their security depends on understanding the feasible attacks. Faraday cages, optical couplers, and power filters would not stop acoustic leakage through vents or self-amplification attacks that induce leakage at frequencies below the filter's design specification. The problem of creating inexpensive hardware or software that adequately mitigates all feasible side-channel attacks thus remains open.

Daniel Genkin, Lev Pachmanov, Itamar Pipman, Adi Shamir, and Eran Tromer
Tel Aviv, Israel

(1) Hewitt, C. Security Without IoT Mandatory Backdoors: Using Distributed Encrypted Public Recording to Catch & Prosecute Suspects. Social Science Research Network, June 16, 2016;

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