2015 – excellent work by Jochen Hoenicke on using an inexpensive oscilloscope to monitor the power drawn by a TREZOR bitcoin wallet to determine what data it was processing.

He writes:

There were some discussions on reddit whether TREZOR, a hardware wallet for securely storing Bitcoins, can be attacked using side channels like power fluctuations, electromagnetic radiations or similar. Such an attack would allow for retrieving the private key that gives access to the Bitcoins stored on the TREZOR. Usually the discussions of side-channel attacks mention the code that signs a Bitcoin transaction. To sign a transaction on the TREZOR, you need to enter the secret PIN first. So this is not useful in the scenario where the attacker has physical access to the device but does not know the PIN.

He explains how you can recover a private key from a TREZOR, if it still runs with firmware 1.3.1.  It is an interesting read on how to take a device and see what is happening inside based on the power it is drawing.

Jochen did the right thing and informed Satoshi Labs of his result first. This is why the latest firmware, 1.3.3, will ask for a PIN when computing the public key. Also Satoshi included his suggested patches in the latest firmware that will reduce the information leaked through side-channels during computation of public keys, signatures, and decryption.

Read the entire investigation on Jochen’s website.

Do you like this type of investigation, let us know in the comments!