Accountability of Things: Large-Scale Tamper-Evident Logging for Smart Devices

Our modern world relies on a growing number of interconnected and interacting devices, leading to a plethora of logs establishing audit trails for all kinds of events. Simultaneously, logs become increasingly important for forensic investigations, and thus, an adversary will aim to alter logs to avoid culpability, e.g., by compromising devices that generate and store logs. Thus, it is essential to ensure that no one can tamper with any logs without going undetected. However, existing approaches to establish tamper evidence of logs do not scale and cannot protect the increasingly large number of devices found today, as they impose large storage or network overheads. Additionally, most schemes do not provide an efficient mechanism to prove that individual events have been logged to establish accountability when different devices interact. This paper introduces a novel scheme for practical large-scale tamper-evident logging with the help of a trusted third party. To achieve this, we present a new binary hash tree construction designed around timestamps to achieve constant storage overhead with a configured temporal resolution. Additionally, our design enables the efficient construction of shareable proofs, proving that an event was indeed logged. Our evaluation shows that - using practical parameters - our scheme can localize any tampering of logs with a sub-second resolution, with a constant overhead of ~8KB per hour per device.