A Comparative Study of Homomorphic and Searchable Encryption Schemes for Cloud Computing

Cloud computing is a popular distributed network and utility model based technology. Since in cloud the data is outsourced to third parties, the protection of confidentiality and privacy of user data becomes important. Different methods for securing the data in cloud have been proposed by researchers including but not limited to Oblivious RAM, Searchable Encryption, Functional Encryption, Homomorphic Encryption etc. This paper focuses on Searchable and Homomorphic Encryption methods. Finally, a comparative study of these two efficient cloud cryptographic methods has been carried out and given here. KeywordsCloud Computing; Security; Homomorphic Encryption; Searchable Encryption I. SECURITY IN CLOUD COMPUTING Cloud Computing is a distributed network meant for providing service by cloud provider to the consumers on rental basis [1]. Owners of data store their data in cloud which therefore need to be secured. By storing data in encrypted form, one can maintain the confidentiality and privacy of data in cloud. Many cryptographic methods have been devised to address the issue of confidentiality and privacy of owner’s data in cloud. An in-depth survey has been done on cloud related security issues, challenges and cryptographic algorithms by Prasanna and Akki [2]. Among them homomorphic and searchable encryption methods are most popular, where one can perform computation and search on ciphertext without disclosing plaintext. The authors focus more on these two techniques in this paper. The paper is organized as follows: Section 2 discusses criteria’s used for developing Homomorphic Encryption methods. The section also briefs some of the known Fully Homomorphic Encryption methods and their corresponding technologies used. Section 3 focuses on related work on Searchable Encryption methods and different criteria’s used to categorize them. Section 4 compares different known cloud cryptographic methods using efficiency and security as parameters. Section 5 concludes with an utter need of efficient cryptographic methods like Searchable Encryption for further study and research. II. HOMOMORPHIC ENCRYPTION In cloud, the primary concern is of maintaining both confidentiality and privacy of owner’s data from untrusted users. The concept of homomorphism introduced in 1978, by Rivest et al [3], can be used for securing the data stored in cloud from unauthorized users. Two messages m1 and m2 are encrypted by using any known encryption method E with public or private key pk, where C1 and C2 are their corresponding ciphertexts (i.e. C1= Epk (m1) and C2= Epk (m2)). The HE scheme performs computation like addition, multiplication etc. between C1 and C2 without decryption. The obtained result is also in encrypted form. The general architecture of the HE scheme is shown in figure 1.