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...     »