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Secure Cloud Storage with Client-Side Encryption Using a Trusted Execution Environment

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Secure Cloud Storage with Client-Side Encryption Using a Trusted Execution Environment Secure Cloud Storage with Client-side Encryption using a Trusted Execution Environment Marciano da Rocha1 a, Dalton Cezane´ Gomes Valadares2;4 b, Angelo Perkusich3 c, Kyller Costa Gorgonio4 d, Rodrigo Tomaz Pagno1 e and Newton Carlos Will1 f 1Department of Computer Science, Federal University of Technology, Parana,´ Dois Vizinhos, Brazil 2Department of Mechanical Engineering, Federal Institute of Pernambuco, Caruaru, Brazil 3Department of Electrical Engineering, Federal University of Campina Grande, Campina Grande, Brazil 4Department of Computer Science, Federal University of Campina Grande, Campina Grande, Brazil Keywords: Intel SGX, Data Sealing, File Encryption, Confidentiality, Integrity, Secure Storage, Cloud Storage. Abstract: With the evolution of computer systems, the amount of sensitive data to be stored as well as the number of threats on these data grow up, making the data confidentiality increasingly important to computer users. Currently, with devices always connected to the Internet, the use of cloud data storage services has become practical and common, allowing quick access to such data wherever the user is. Such practicality brings with it a concern, precisely the confidentiality of the data which is delivered to third parties for storage. In the home environment, disk encryption tools have gained special attention from users, being used on personal computers and also having native options in some smartphone operating systems. The present work uses the data sealing, feature provided by the Intel Software Guard Extensions (Intel SGX) technology, for file encryption. A virtual file system is created in which applications can store their data, keeping the security guarantees provided by the Intel SGX technology, before send the data to a storage provider. This way, even if the storage provider is compromised, the data are safe. To validate the proposal, the Cryptomator software, which is a free client-side encryption tool for cloud files, was integrated with an Intel SGX application (enclave) for data sealing. The results demonstrate that the solution is feasible, in terms of performance and security, and can be expanded and refined for practical use and integration with cloud synchronization services. 1 INTRODUCTION CEOs are concerned with the state of the cyber secu- rity of their company (PwC, 2016). Cyber attacks and different cybercrimes are an in- Nowadays, users are increasingly using cloud creasing threat to today’s digital society (Huang et al., storage services to keep their files and can access 2018; Khraisat et al., 2019; Singh et al., 2019). In them from any device connected to the Internet. Such this context data governance and security is of utmost storage services hold a large set of data from various importance (Onwujekwe et al., 2019). Reports from users, including sensitive and confidential informa- specialized companies and government security enti- tion, due to their reliance on such providers. However, ties indicate a growing number of threats to digital these storage services do not always guarantee or re- data, whether from corporations or users. Companies spect the privacy of their users (Branscombe, 2015; faced an average of 25 new threats per day in 2006, Cox, 2016; Clover, 2017). up from 500,000 in 2016 (Weafer, 2016) and 61% of One way to ensure an additional level of security for users’ sensitive files is to encrypt such data be- a https://orcid.org/0000-0002-8213-6803 fore sending them to the cloud storage server. One b https://orcid.org/0000-0003-1709-0404 option that performs such an operation is using a disk c https://orcid.org/0000-0002-7377-1258 encryption system, which runs in the operating sys- d https://orcid.org/0000-0001-9796-1382 tem background and encrypts all information that is e https://orcid.org/0000-0001-9267-4982 stored. f https://orcid.org/0000-0003-2976-4533 This type of system has some vulnerabilities, 31 da Rocha, M., Valadares, D., Perkusich, A., Gorgonio, K., Pagno, R. and Will, N. Secure Cloud Storage with Client-side Encryption using a Trusted Execution Environment. DOI: 10.5220/0009130600310043 In Proceedings of the 10th International Conference on Cloud Computing and Services Science (CLOSER 2020), pages 31-43 ISBN: 978-989-758-424-4 Copyright c 2020 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved CLOSER 2020 - 10th International Conference on Cloud Computing and Services Science which can highlight the risk of attacks and improper • The proposal to improve the security of disk/file access to data. One of these vulnerabilities is the encryption process using Intel SGX; user’s password choice, which is often weak and can • The implementation of such proposal consider- be discovered using dictionary attacks, default pass- ing an Intel SGX application integrated with the words, rainbow tables or even brute force. Another Cryptomator tool; factor is that most of the existing disk encryption sys- tems keep the encryption key in main memory while • The performance evaluation of our proposal im- it is running, allowing other malicious applications to plemented, considering six different hardware attack and discover the key. combinations. Nowadays the use of reliable trusted hardware The remainder of this paper is organized as fol- technologies, such as Intel Software Guard Exten- lows: Section 2 provides background information sions (Intel SGX) (INTEL, 2014) and ARM Trust- about the cloud storage and disk encryption tech- Zone (Pinto and Santos, 2019), has grown. An In- niques, as well the Intel Software Guard Extensions tel SGX application creates an isolated protected re- technology; Section 3 presents previous research gion of memory, which is called enclave, where data closely related to our proposal, in the field of cloud are securely processed. Among the various features storage security and the use of Intel SGX in file en- provided by the SGX technology, there is the seal- cryption; Section 4 describes the solution proposed by ing of an enclave data in secondary memory. This this paper; in order to validate the proposed approach, process uses a unique key as a basis for the encryp- three prototypes are presented in Section 5 as a proof tion, which is generated by combining a developer of concept; Section 6 presents the performance evalu- key and a processor key, and is not stored in mem- ation of the prototype on six different hardware com- ory: it is generated again to each request, guarantee- binations; the threat model as well the security eval- ing that the data will be decrypted only by the enclave uation of the Intel SGX technology and the proposal that sealed them, in the platform in which they were solution are presented in Section 7; the limitations of sealed (Anati et al., 2013). Another feature provided our solution are described in Section 8 and, finally, by Intel SGX technology is the encryption of data in a Section 9 concludes the paper and presents the future region of primary memory with a random key that is works. generated with each power cycle. This key is known only by the processor and never goes beyond its limits (INTEL, 2016). According to the previous discussion, we estab- 2 BACKGROUND lished the following two research questions to guide our research: This Section presents a brief description of important concepts used in this work, such as cloud storage, disk 1. How to improve the security of traditional disk en- encryption and the Intel Software Guard Extensions. cryption tools? 2. How to decrease the user’s need to trust the cloud 2.1 Cloud Storage service provider? In this paper, we propose the use of Intel SGX Nowadays, more users are using cloud storage ser- features to perform data sealing and processing in vices, either explicitly to keep their personal files, or a more secure way, since these operations are per- implicit through applications that make use of such formed only inside an enclave, which is supposed to background services to maintain backups or history be protected even against adversaries with high priv- of user data. The benefits inherent in cloud data stor- ileges inside the operating system. We implemented, age are virtually unlimited storage, version history for as a proof of concept, an application using the Cryp- each file, and access to data at any time from any de- tomator, an open source client-side encryption tool vice connected to the Internet. used for cloud files protection. The Cryptomator was But there is always a concern regarding the se- modified, integrated with an Intel SGX application, curity of data stored in the cloud, especially as the in order to use its data sealing feature, which is per- number of constant cyber attacks intensifies. One of formed only inside an enclave. With this, the data the most promising defenses for the cloud is encryp- encryption/decryption processes are performed in a tion, which offers robust protection in both data stor- more secure way, extending this security also for the age and transit. Encryption is available in two main keys, since they are also handled inside the enclave. security configurations: client- and server-side. The main contributions of this work are listed be- With server-side encryption, the cloud storage low: provider manages encryption keys along with their 32 Secure Cloud Storage with Client-side Encryption using a Trusted Execution Environment data, and many cloud storage providers use this failures in the encryption process, allowing the stored method. This limits the complexity of the environ- data to be extracted from the drive without knowing ment while maintaining the isolation of your data, but the key used to perform the encryption. there are several risks of keeping the encryption key Software-based FDE engines are applications run and data encrypted by it in the same place. In ad- at the kernel level by the CPU, in which data and dition, the cloud provider itself can access keys and used keys are stored in the main memory.
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