Ledger Donjon decrypts Blockstream Jade firmware via ESP32 side channel

At Black Hat USA 2022 Ledger Donjon researchers Karim M. Abdellatif, Olivier Hériveaux and Adrian Thillard presented a side-channel attack that breaks the flash encryption of Espressif’s ESP32-V3 microcontroller, using the Blockstream Jade as the practical target. Ledger published a write-up on 15 February 2023, and the technical paper appeared on IACR ePrint (2023/090).

According to Donjon, the Jade’s firmware sits encrypted in an external flash chip. By measuring power consumption while the chip decrypts that flash at start-up, the researchers recovered the AES-256 key with correlation power analysis; against a real Jade they removed the ESP32, collected about 500,000 traces in about 2 hours and recovered the key. The decrypted firmware contains the keys the device uses to talk to Blockstream’s blind PIN server. Donjon notes that the PIN is not stored in the flash and is verified remotely by that server, and describes the result as enabling cloning the wallet and injecting a backdoor that sends transactions to substituted addresses, an evil-maid scenario; the write-up does not claim the seed or PIN were extracted.

The researchers say they first contacted Blockstream and Espressif in October 2021. Espressif published advisory AR2022-003 and, according to the researchers, said future products would include countermeasures; the slides add that the ESP32-S2, -C3 and -S3 are also impacted. Neither Ledger’s write-up nor the talk describes a Blockstream response or firmware fix.