Encrypted Data Deduplication in Cloud Storage

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1 Encrypted Data Deduplication in Cloud Storage Chun- I Fan, Shi- Yuan Huang, Wen- Che Hsu Department of Computer Science and Engineering Na>onal Sun Yat- sen University Kaohsiung, Taiwan AsiaJCIS 2015

2 Outline Introduction Related Works The Proposed Mechanism The Performance of Data Compression Compare with Existing Mechanisms Conclusion 2

3 Cloud Storage Client users upload and store their data on the cloud storage. When their need their data, they download from the cloud storage. 3

4 Two Important Issues in Cloud Storage 1. Data Compression For cloud storage server, it wants to compress the stored data, and reduce the consumption of the storage space. 2. Privacy Preservation For client users, they don t want to leak any information from the stored data. 4

5 Two Important Issues in Cloud Storage 1. Data Compression For cloud storage server, it wants to compress the stored data, and reduce the consumption of the storage space. Cloud storage server uses data deduplication technique to eliminate the redundant data. 2. Privacy Preservation For client users, they don t want to leak any information from the stored data. 5

6 Data Deduplication Technology Source-Based Approach Data deduplication acts on the client users. Client users need to query storage server whether the data has been uploaded, before really uploading. (1) File ID (2) Yes / No Client User (3) File / Metadata Target-Based Approach The steps of data deduplication are handled by the storage server, while client users just upload and download their data. Upload - Search for redundant data - Eliminate duplicate content Download - Rebuild the eliminated content 6

7 Two Important Issues in Cloud Storage 1. Data Compression For cloud storage server, it wants to compress the stored data, and reduce the consumption of the storage space. Cloud storage server uses data deduplication technique to eliminate the redundant data. 2. Privacy Preservation For client users, they don t want to leak any information from the stored data. 7

8 Two Important Issues in Cloud Storage 1. Data Compression For cloud storage server, it wants to compress the stored data, and reduce the consumption of the storage space. Cloud storage server uses data deduplication technique to eliminate the redundant data. 2. Privacy Preservation For client users, they don t want to leak any information from the stored data. Client users encrypt the uploaded data, before really upload it. 8

9 Encrypted Data Deduplication The goal of encryption is to keep the information secret and to make the ciphertext difficult to distinguish from a random value. 1. Make the ciphertexts be identifiable Make the same plaintexts produce to the same ciphertexts, and the cloud storage server can directly identify the redundancy on ciphertext. 2. Identify the contents of ciphertexts Add a check tag, such like ID of files, and make the cloud storage server can identify the redundancy. 9

10 Existing Encrypted Data Deduplication Convergent Encryption The secret key is the hash value of the plaintext. Data owner encrypts the plaintext by a symmetric encryption PS: Because the same plaintext produces the same ciphertexts, convergent encryption is generally used on data deduplication. 10

11 Encrypted Data Deduplication The goal of encryption is to keep the information secret and to make the ciphertext difficult to distinguish from a random value. 1. Make the ciphertexts be identifiable Make the same plaintexts produce to the same ciphertexts, and the cloud storage server can directly identify the redundancy on ciphertext. 2. Identify the contents of ciphertexts Add a check tag, such like ID of files, and make the cloud storage server can identify the redundancy. 11

12 Notations A uploaded file An one-time AES key, which is randomly selected by the client user and used to encrypted the uploaded data The public-private key pair of client user (a homomorphic encryption) Two cryptographic hash functions, and The encryption and decryption algorithm of the AES encryption The encryption and decryption algorithm of a homomorphic encryption The operator of the homomorphic encryption, where = where is a prime modulus 12

13 Packaging Data as Cipher Structure 1. Check Block () Compute the hashed value of the file: 2. Cipher Block () Generate a random AES key Encrypt the file using by the AES encryption: Client User 3. Enabling Block () Encrypt using her/his own public key by the homomorphic encryption: 4. Converting Block () Compute the second hashed value of the file: Multiply by mod : mod 13

14 Encrypted Data Deduplication Alice Upload First Upload Second Bob Convert the Enabling Block: 1) Compute the conversion factor: mod mod mod 2) Encrypt the conversion factor using the public key of Bob: 3) Convert the enabling block of Bob: 14

15 The Proposed Scheme 15

16 Security Analysis Check Block and Converting Block: The check block is the hash value of the content, and the converting block is the hash value compute with a random AES key. Because the hash value is retrieve, it is hard to obtain the content from the check block and the random AES key form the converting block. Enabling Block and Cipher Block: The content is encrypted by the AES encryption in the cipher block and the random AES key is encrypted by the homomorphic encryption in the enabling block. Therefore, the enabling block and the cipher block are the formal digital envelope and it is as secure as encrypting the content by the homomorphic encryption directly. 16

17 Performance of Data Compression Storing in Plaintext Format: For the cloud storage server, the stored data are not encrypted. Storing in Ciphertext Format (I): Client users encrypt the uploaded data as digital envelope (RSA + AES) to encrypt. Storing in Ciphertext Format (II): Client users encrypt the uploaded data as digital envelope (RSA + convergent) to encrypt. Storing in SEDDM Format: All the upload data are packaged as the cipher structure, which consists of a check block, a converting block, an enabling block, and a cipher block. 17

18 Performance of Data Compression Storing in Plaintext Format: Plaintext = 65,536 bytes Storing in Ciphertext Format (I): Encrypted Random Key = 256 bytes Ciphertext = 65,536 bytes Storing in Ciphertext Format (II): Encrypted Random Key = 256 bytes Ciphertext Check Block: = 65,536 bytes Enable Block: Hash 1 (F)=64 bytes HE Enc ( PK U i, K A )= 32/256 Storing Converting Proposed Block: Format: 512=512 bytes K A Hash 2 (F) mod p=64 bytes Cipher Block: AES Enc ( K A,F )= 65,536/16 16=65,536 bytes 18

19 Performance of Data Compression 19

20 Comparison with Existing Mechanisms 20

21 Conclusion Data Confidentiality is opposite to Data Deduplication. We propose an encrypted data deduplication mechanism: Avoiding the cloud storage server obtaining the sensitive information from the stored data The performance of data compression: The proposed mechanisms are similar to the performance of storing in the plaintext format. Comparing with the existing mechanisms: The proposed mechanisms improve privacy preservation. 21

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