## 7 Related Work  
In this section, we conducted a literature review in the area of remote memory attestation, which is closely related to our study. In a trusted computing environment, remote attestation generally requires specific hardware, which is commonly called the trusted platform module (TPM) [29]. Nonetheless, remote attestation schemes based on the TPM [30] cannot be directly applied to the smart grid because of the limitation of hardware and software on specific devices deployed in the smart grid. To avoid the limitation of the hardware, software-based attestation schemes have been developed for legacy systems. For example, [PERSON] _et al._ proposed a software-based attestation for embedded devices called SWATT [11]. In SWATT, the verifier sends a challenge request to remote devices, which activates the verification procedure on remote devices with a generated checksum. Then, remote devices respond to the checksum of the verifier. Notice that if the adversary launches the memory verification attack that attempts to compute the correct checksum, the verifier can still detect the slowdown raised by the extra if statements. [PERSON] _et al._ also proposed FIRE (Forgery-resilient Intrusion detection, Recovery, and Establishments of keys) [31], SCUBA (Secure Code Update By Attestation) [9] and SAKE (Software Attestation for Key Establishment) [32], which all use indisputable code execution (ICE) to verify the correction of memory in remote devices based on the response time of remote devices. In addition, [PERSON] _et al._ proposed a verification called Pioneer [33], which verifies the code integrity and enforces untampered code execution on an untrusted legacy host.  
[PERSON] _et al._ proposed a one-way memory attestation protocol (OMAP) for smart meters [10], which uses built-in values as challenges to compute the checksum. Although OMAP does not need the challenge sent from the verifier, it may be subject to the memory replication attack. [PERSON] _et al._ proposed a software-based attestation technique, namely SMATT [34], to address issues, including the verification overhead for large-scale networks and the evasion of attestation by the memory replication. Nonetheless, SMATT requires a public key infrastructure (PKI), which is considered as the basis for the secure communication between smart meters and verifiers. Nonetheless, using the public key in the smart grid is still questionable due to the hardware and software deployment in the smart grid, which consists of a number of heterogeneous devices. [PERSON] proposed an attestation scheme, namely CAK (cumulative attestation kernel) [35], which addresses the inconsistencies of time-of-use-to-time-of-check (TOUTTOC). CAK is a cumulative attestation for embedded systems to prevent the attack in the verification process. It requires asymmetric key pairs for devices, which limit its use in the smart grid.  
In this paper, we proposed a low-cost remote memory attestation for the smart grid. Different from existing attestation schemes, our proposed attestation scheme takes into account the impacts of the network delay on the detection of remote nodes and does not require key management and specific hardware or software support. Therefore, our proposed scheme can be useful in the smart grid that consists of numerous legacy devices.