On Coldcard MK1 and MK2 devices, a side channel for the row-based OLED display was found.

Summary

On Coldcard MK1 and MK2 devices, a side channel for the row-based OLED display was found. The power consumption of each row-based display cycle depends on the number of illuminated pixels, allowing a partial recovery of display contents. For example, a hardware implant in the USB cable might be able to leverage this behavior to recover confidential secrets such as the PIN and BIP39 mnemonic. In other words, the side channel is relevant only if the attacker has enough control over the device's USB connection to make power-consumption measurements at a time when secret data is displayed. The side channel is not relevant in other circumstances, such as a stolen device that is not currently displaying secret data. On Coldcard MK1 and MK2 devices, a side channel for the row-based OLED display was found. The power consumption of each row-based display cycle depends on the number of illuminated pixels, allowing a partial recovery of display contents. For example, a hardware implant in the USB cable might be able to leverage this behavior to recover confidential secrets such as the PIN and BIP39 mnemonic. In other words, the side channel is relevant only if the attacker has enough control over the device's USB connection to make power-consumption measurements at a time when secret data is displayed. The side channel is not relevant in other circumstances, such as a stolen device that is not currently displaying secret data. NOTE: At Coinkite, we’ve already mitigated it, even though we feel strongly that it is not a legitimate issue. In our opinion, it is both unproven (might not even work) and also completely impractical—even if it could be made to work perfectly