## 2 Literature Review
### Smart Economy
#### 2.6.2 Countermeasures  
Under the same assumption, this research [128] focuses on the relevance of mobility and the strength of elliptic curve cryptography in heterogeneous wireless sensor networks to secure smart city applications. The results of the various simulations revealed that the proposed dynamic approach to secure smart city applications algorithm improves application security by lowering the energy consumption, the number of calculations required, and the storage space necessary for the elliptic curve cryptography keys. In particular, in the proposed approach, a powerful mobile cluster head performs operations that demand more computation and use more battery sensors regularly, such as the development, maintenance, and distribution of elliptic curve cryptography keys and periodic rekeying. Because the powerful mobile cluster head has no energy limits and is considered impenetrable, it is a periodic distributor of cryptographic keys to all the data sensors in different applications. However, the internet-based economy creates several threats, such as unlawful data copying and digital copyright infringement, posing the problem of preserving the security and copyright of important data housed in databases. This study [122] presents a unique approach, Lossless Database Watermarking in the Homomorphic Encryption domain (HOPE-L), to solve this difficulty. The method combines database encryption (homomorphic encryption, order-preserving encryption) and information concealing (lossless data-based watermarking) technologies. To be more explicit, the information concealing technique uses the homomorphic encryption algorithm's features to incorporate hidden data. Throughout the data-embedding process, no distortion is introduced. As a result, the proposed approach combines the watermark within the encrypted data without losing any information. The watermark may validate the copyright, and the receivers can retrieve the original database without losing any data. Theorem and analysis show that HOPE-L can attain additional embedding space without distortion. Extensive testing demonstrates that the operating method is time-efficient, the embedded watermark is resilient, and HOPE-L outperforms previous techniques and can withstand typical database assaults. In contrast, the creative contribution of blockchain to smart economy activities may enhance corporate operations and provide a real-time view of all financial data. On-demand products, for example, of a signed contract in the shortest period feasible, may considerably assist financial operations. This process's approval time is too lengthy, creating an opportunity to use blockchain as a solution. As a consequence of merging the smart economy with cutting-edge technology, company operations in smart cities may be strengthened by safely using smart contracts in day-to-day activities. This project [123] focuses on the document of understanding (DOU) contract, which serves as the foundation for the relationship between a consumer service and the supplier of that service. The authors leveraged local resources and used design thinking and agile principles to construct a local blockchain ledger for this assignment. As a result, they produced a proof-of-concept blockchain demo that has the whole precise history of the agreement, with immutable transactions and transparency, while providing protection and privacy to the participant's information. They registered the time required to obtain the DOU contract signed off by everyone engaged in the process with this demo, significantly improving it. It may also be reproduced in other areas that handle sensitive data and financial reporting. It must be noted that advanced persistent threat (APT) attacks [129] are one of the significant security challenges confronting smart economy sectors in smart cities. APT is a stealthy threat actor that acquires unauthorized network access and stays undiscovered for a lengthy period.