Retrofitting Leakage Resilient Authenticated Encryption to Microcontrollers

The security of Internet of Things (IoT) devices relies on fundamentalconcepts such as cryptographically protected firmware updates. In this contextattackers usually have physical access to a device and therefore side-channel attackshave to be considered. This makes the protection of required cryptographic keysand implementations challenging, especially for commercial off-the-shelf (COTS)microcontrollers that typically have no hardware countermeasures. In this work, wedemonstrate how unprotected hardware AES engines of COTS microcontrollers canbe efficiently protected against side-channel attacks by constructing a leakage resilientpseudo random function (LR-PRF). Using this side-channel protected building block,we implement a leakage resilient authenticated encryption with associated data(AEAD) scheme that enables secured firmware updates. We use concepts fromleakage resilience to retrofit side-channel protection on unprotected hardware AESengines by means of software-only modifications. The LR-PRF construction leveragesfrequent key changes and low data complexity together with key dependent noise fromparallel hardware to protect against side-channel attacks. Contrary to most otherprotection mechanisms such as time-based hiding, no additional true randomness isrequired. Our concept relies on parallelS-boxesin the AES hardware implementation,a feature that is fortunately present in many microcontrollers as a measure to increaseperformance. In a case study, we implement the protected AEAD scheme for twopopular ARMCortex-Mmicrocontrollers with differing parallelism. We evaluate theprotection capabilities in realistic IoT attack scenarios, where non-invasive EM probesor power consumption measurements are employed by the attacker. We show thatthe concept provides the side-channel hardening that is required for the long-termsecurity of IoT devices.      «

The security of Internet of Things (IoT) devices relies on fundamentalconcepts such as cryptographically protected firmware updates. In this contextattackers usually have physical access to a device and therefore side-channel attackshave to be considered. This makes the protection of required cryptographic keysand implementations challenging, especially for commercial off-the-shelf (COTS)microcontrollers that typically have no hardware countermeasures. In this work, wedemonstrate how unprotecte...     »