Ledger Donjon recovers Coldcard Mk2 PIN and seed by laser fault injection

On 18 May 2020 Ledger’s security team, Donjon, disclosed an attack on the Microchip ATECC508A secure memory chip used in the Coldcard Mk2. Ledger says it found the chip vulnerability in May 2019, shared full details with Microchip in June 2019 and also notified Coinkite; it presented the work at SSTIC 2020.

According to Donjon, laser fault injection bypasses the chip’s access checks so that data slots configured as secret, such as the PIN slot and the pairing secret, can be read out. From there an attacker can either brute-force the PIN hash offline to learn the PIN, or talk to the chip directly to read and decrypt the seed. The attack is invasive: the case is opened, the chip desoldered, its package milled down to the silicon and mounted on a laser platform. Ledger estimates the equipment at about $200,000 and describes the work as requiring serious expertise.

Coinkite states the research does not affect the Coldcard Mk3, which had already moved to the ATECC608A and added a PIN attempt limit before Ledger’s report; Ledger likewise says the Mk3 is not impacted. Coinkite says the steps allow only one attempt each and that probably only nation-state-like actors could carry them out, and argues the $200,000 figure understates the skill involved. There is no firmware fix for the Mk2 chip.

What Coinkite advises:

• Consider upgrading to the Coldcard Mk3.