Encryption key stolen by examining a power LED

And side channel it is a source of information that can be used to acquire details about the behavior or characteristics of a system, even when this data is not explicitly disclosed. We have seen what side channel attacks are in the case of processors and when they can be dangerous. A new frontier is represented by the possibility of subtracting the cryptographic key during the operation of major smart card readers and other similar devices using a system based on video cryptanalysis. Without resorting to expensive equipment or launching invasive attacks.

What are attacks Key-leaking side channel

The attacks Key-leaking side channel exploit the information ofside channel” to get sensitive information, such as encryption keys and other confidential data. The attackers analyze data associated with the system operation, such as power consumption, run time or electromagnetic radiation. Subtle details about system behavior can reveal information about the cryptographic keys in use.

In a encrypted teleprinter that the United States Army and Navy used during World War II to transmit communications that were not to be read by German and Japanese spies, one of the side channel oldest known to date. By entering a specific letter, then automatically encrypted, the operation highlighted a unique behavior on a oscilloscope place nearby. And this to the great amazement of the engineers of the Bell Labs who designed the terminal.

Although the cryptographic algorithm used in the device itself was valid, the electromagnetic emissions enacted were sufficient to provide an attacker with a useful tool to derive the secret key.

Steal a cryptographic key by examining the behavior of a power LED

A well-known researcher, Ben Nassi, demonstrated how it is possible to derive a cryptographic key using an advanced video analysis technique. Using a camera pointing at the smart card reader equipped with an operating LED, it is possible to successfully extract a chiave ECDSA a 256 bit.

I Power LED they are designed to indicate when a device is turned on. They typically emit a light that varies in brightness e color depending on the power consumption of the connected device. This is due to the fact that in many devices the LED is connected directly to the supply line of the electric circuit, without using filters and voltage stabilizers.

One of the most significant aspects of the work conducted by Nassi lies in the fact that the attacker does not have to connect probes, equip himself with an oscilloscope or work on radio frequencies. Just take care to properly adjust the sampling rate intensity/brightness of the power LED (method rolling shutter).

Evidence of the video cryptanalysis used to trace the cryptographic key has been published on YouTube

The demo posted on YouTube shows the process of video capture which portrays the LED behavior of a smart card reader while performing cryptographic operations. The same thing was done in order to extract the SIKE key from a smartphone Samsung Galaxy S8. The SIKE key (Supersingular Isogeny Key Encapsulation) rests its operation on a public key cryptographic algorithm developed to be resistant to post-quantum attacks. Described as resistant to attacks made by the use of quantum computersHowever, SIKE was recently defeated with an older Xeon-based system.

To the naked eye, the captured video da Nassi seems insignificant. Analyzing i video frames for different RGB values ​​in the green channel, an attacker can identify the start and end of a cryptographic operation. The origin of vulnerability it’s in cryptographic libraries; however, the power LEDs provide the infrastructure needed to visually exploit the safety issue.

At least six smartcard readers from five manufacturers sold on Amazon are vulnerable to a direct attack. Samsung Galaxy S8 is vulnerable to an indirect attack“, Nassi explains. “And there are likely other devices out there that are vulnerable to video-based cryptanalysis“.

The researchers recommend several countermeasures that manufacturers can take to strengthen devices against video cryptanalysis. Chief among these is avoiding the use of power LEDs by integrating for example a capacitor that works as a “low-pass filter”. Another option is to use an op amp between the power rail and the power LED.


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