Remote mobile and embedded devices are used to deliver increasingly impactful services, such as medical rehabilitation and assistive technologies. Secure system logging is beneficial in these scenarios to aid audit and forensic investigations particularly if devices bring harm to end-users. Logs should be tamper-resistant in storage, during execution, and when retrieved by a trusted remote verifier. In recent years, Trusted Execution Environments (TEEs) have emerged as the go-to root of trust on constrained devices for isolated execution of sensitive applications. Existing TEE-based logging systems, however, focus largely on protecting server-side logs and offer little protection to constrained source devices. In this paper, we introduce EmLog -- a tamper-resistant logging system for constrained devices using the GlobalPlatform TEE. EmLog provides protection against complex software adversaries and offers several additional security properties over past schemes. The system is evaluated across three log datasets using an off-the-shelf ARM development board running an open-source, GlobalPlatform-compliant TEE. On average, EmLog runs with low run-time memory overhead (1MB heap and stack), 430--625 logs second throughput, and five-times persistent storage overhead versus unprotected logs.
@cite_10: In many real-world applications, sensitive information must be kept it log files on an untrusted machine. In the event that an attacker captures this machine, we would like to guarantee that he will gain little or no information from the log files and to limit his ability to corrupt the log files. We describe a computationally cheap method for making all log entries generated prior to the logging machine's compromise impossible for the attacker to read, and also impossible to modify or destroy undetectably.
@cite_22: 
@cite_25: Trustable log data is essential in digital forensic investigations in order to allow reliable reconstruction of events. Existing solutions do not provide adequate protection, exposing the log-producing application to software-based attacks. In this paper we provide a solution based on Trusted Computing using a Trusted Platform Module (TPM) and AMD’s Secure Virtual Machine technology (SVM). While current solutions only protect against manipulation of existing logs, we go one step further by establishing hardware-based trust in the log producing application. Our solution ensures confidentiality, integrity and non-repudiation during creation, storage and transmission of log data.
@cite_2: Auditing system logs is an important means of ensuring systems' security in situations where run-time security mechanisms are not sufficient to completely prevent potentially malicious activities. A fundamental requirement for reliable auditing is the integrity of the log entries. This paper presents an infrastructure for secure logging that is capable of detecting the tampering of logs by powerful adversaries residing on the device where logs are generated. We rely on novel features of trusted hardware TPM to ensure the continuity of the logging infrastructure across power cycles without help from a remote server. Our infrastructure also addresses practical concerns including how to handle high-frequency log updates, how to conserve disk space for storing logs, and how to efficiently verify an arbitrary subset of the log. Importantly, we formally state the tamper-proofness guarantee of our infrastructure and verify that our basic secure logging protocol provides the desired guarantee. To demonstrate that our infrastructure is practical, we implement a prototype and evaluate its performance.
Early work by @cite_22 explored trusted hardware (Java iButton) to protect the initial PSK of the Schneier and Kelsey scheme @cite_10 . Later, @cite_2 suggested a using a TPM with a forward integrity scheme based on branched key chaining. Logs are divided into epochs (blocks), each comprising a sequence of hash-chained log entries (sub-epochs). The root entries of each epoch are hash-chained with past epochs, which creates a two-dimensional hash chain to prevent in which an attacker re-orders log blocks to mislead auditors. For each new epoch, the previous epoch's logs are securely stored using the TPM's seal functionality, which encrypts the logs with a TPM-bound key so only that particular TPM can decrypt unseal' them. B "o @cite_25 explore the use of AMD's Secure Virtual Machine (SVM) -- an early inception of the TEE -- for launching a syslog client daemon and logging application from the TPM's secure boot chain. The logger executes with access to TPM-bound key-pairs for encrypting and signing log entries. Upon request, the logs are decrypted and transmitted to the verifying party; the TPM keys are certified for authenticating that signed logs originated from the SVM.