# Cloud Storage Data Verification Using Signcryption Scheme
## 1 Introduction  
Cloud computing is not a new concept and has had rapid development since it was first introduced. Cloud computing serves various services that bring convenience to its users. This technology allows users to employ computational resources and services such as infrastructure, storage, and applications--well-known cloud service providers (CSPs) such as AWS, Azure, Google Cloud, and IBM. It enables users to access their data every time from everywhere. Unfortunately, cloud computing also comes with security challenges such as unreliable CSPs [1; 2]. Users grant CSPs the right to do any operation on their data when they outsource data to CSPs. As a result, the user has limited control over what happens to their data. Furthermore, because the original data is already kept in CSPs, users may remove it from their local storage. The ability of CSPs to conceal errors from users for their own gain is a serious issue with loss of data possession [3; 4]. Additionally, CSPs could encounter internal or external security issues, including mistakenly erasing or modifying infrequently accessed user data to lessen storage requirements and claims that all data is still saved in the cloud [2]. Data integrity could also be in danger if a malicious actor infiltrated the CSPs' systems [1; 2; 3; 4; 5]. Therefore, data integrity verification is necessary to ensure the integrity of users' data stored in cloud storage. In the data verification process, it is impractical and inefficient for the verifier to download all the data in advance because stored data may be huge. Additionally, the verifier might not have sufficient resources. More importantly, there is no assurance of neutral data verification, and thus endangers users' privacy. As a result, numerous studies have been conducted to provide auditing protocols for cloud systems. A survey in [2] describes some desirable properties of data auditing protocol. There are three main properties that are vital to the verification process. * Public verifiability. The size of data to be verified may vary. Users may have limited resources which can cause an expensive verification process cost. Therefore, public verifiability enables other parties to do a verification process. * Privacy-preserving. Prevent data leaks to the verifier during the verification process. Concerns about data privacy arise as a result of the public verifiability characteristic. This property requires that the verifier, as an outsider, not receive any confidential information but still be able to verify the data integrity. * Blockless verification. The verifier does not need to download all the data for the verification process. Furthermore, it will decrease communication overhead at the server and increase the efficiency of the verification scheme. Research on data integrity verification in cloud servers without having access to all of the data is particularly attracting attention. [PERSON] et al. [6] are pioneers in addressing this problem. Provable data possession (PDP) is the auditing mechanism that the authors suggested. They present the idea of probabilistically verifying the data integrity kept on the cloud server by users. Users could effectively validate the data integrity using this method without having to save the original data locally. Proof of retrievability (PoR) is the proposed idea put out by the authors of [7]. They use spot-checking and error-correcting codes on remote storage systems to assure data ownership and retrievability. However, those two schemes do not support privacy-preserving to prevent data leaks to the verifier and public verifiability properties. In [8], the authors suggested using signature-then-encryption as part of a public data integrity verification approach for cloud storage. Privacy-preserving is provided through encryption and public verifiability property through generating the tag signature of the data using an algebraic signature. Unfortunately, this scheme lacks the blockless verification property.