a survey on secure cloud data storage zeng, xi 1010105140 cai, peng 1010121750
TRANSCRIPT
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A Survey on Secure A Survey on Secure Cloud Data StorageCloud Data Storage
ZENG, Xi 1010105140
CAI, Peng 1010121750
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Outsource your data to the cloudOutsource your data to the cloud
• Cloud data storage is a rising business model.
2
Mobile devices
Individual users
Enterprises
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Cloud Data StorageCloud Data Storage
• A cost-saving business solution:• Save cost for unused storage• Save technical support for data backups• Save electric power and maintenance costs for data
centers
• As a cloud client, how do we provide security guarantees for our outsourced data?
• Privacy• Data Availability• Data Integrity
• Consistency• Access Control• Assured Deletion
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Security ChallengesSecurity Challenges
• Can we protect outsourced data from improperly accessed?• Unauthorized users must not access our data• We don’t want cloud providers to mine our data for their
marketing purposes
• We need access control:• Only authorized parties can access outsourced data
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Security ChallengesSecurity Challenges
• Can we reliably remove data from cloud?• We don’t want backups to exist after pre-defined time
• e.g., to avoid future exposure due to data breach or error management of operators
• If an employee quits, we want to remove his/her data• e.g., to avoid legal liability
• Cloud makes backup copies. We don’t know if all backup copies are reliably removed.
• We need assured deletion:• Data becomes inaccessible upon requests of deletion
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Secure and E cient Access to ffiSecure and E cient Access to ffiOutsourced DataOutsourced Data
• W. Wang, Z. Li, R. Owens, and B. BhargavaW. Wang, Z. Li, R. Owens, and B. Bhargava
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Wang’s Approach• Aims for designing an approach to achieve flexible access
control and large-scale dynamic data management in a high secure and efficient way.
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Wang’s Approach• Data Access Procedure
• Owner-write-user-read Scenario• Data can be updated only by the original owner• Users read the information according to access rights
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Wang’s Approach• Key generation
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Wang’s Approach• Dynamics Handling
• User Access Right• Eavesdropping
• Over-encryption• Lazy revocation
• Outsourced Data• Deletion• Insertion and appending• Updating
• Control block• One-to-one mapping hierarchy
• Overhead Analysis• Limited storage overhead
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Wang’s Approach• Advantages
• Low clients’ responsibilities• Low storage overhead• Block insertion, update, deletion and appending
• Disadvantages• Requires support from the cloud side• No multiple policies combination
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FADE: FADE: a secure overlay cloud storage a secure overlay cloud storage system with system with FFile ile AAssured ssured DeDeletionletion• Yang Tang, Patrick P. C. Lee, John C. S. Lui, and Radia PerlmanYang Tang, Patrick P. C. Lee, John C. S. Lui, and Radia Perlman
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FADEFADE• A new policy-based file assured deletion scheme that
reliably deletes files of revoked file access policies• Implement a working prototype of FADE atop Amazon S3• Evaluate the performance overhead of FADE atop
Amazon S3
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Policy-based File Assured DeletionPolicy-based File Assured Deletion• Each file is associated with a data key and a file access
policy• Each policy is associated with a control key• All control keys are maintained by a key manager• When a policy is revoked, its respective control key will be
removed from the key manager
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• Main idea:• File protected with data key• Data key protected with control key
FileFile
data key control key
is maintained by the key manager
Policy-based File Assured DeletionPolicy-based File Assured Deletion
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• When a policy is revoked, the control key is removed. The encrypted data key and hence the encrypted file cannot be recovered
• The file is deleted, i.e., even a copy exists, it is encrypted and inaccessible by everyone
FileFile
data keyCannot be recovered
without
Policy-based File Assured DeletionPolicy-based File Assured Deletion
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Multiple Policies
• Conjunctive policies• Satisfy all policies
to recover file
FileFile
P1
P2
P3
Disjunctive Disjunctive policiespolicies• Satisfy only one Satisfy only one
policy to recover policy to recover filefile
FileFile
P1 P2 P3
{F}K {{K}S1}S2 … }Sm S1e1, S2
e2, …, Smem
{F}K {K}S1 ,{K}S2 ,{K}Sm ,S1e1, S2
e2, …, Smem
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System Entities
• Data owner: the entity that originates data to be stored on cloud
• Key manager: maintains policy-based control keys for encrypting data keys
• Cloud: third-party cloud provider (e.g., Amazon S3) that stores data
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Architecture of FADE
• FADE decouples key management and data management• Key manager can be flexibly deployed in another trusted
third party, or deployed within data owner• No implementation changes on cloud
keymanager
…Data
owner
Cloud
file(encrypted)
metadatafile
FADE
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File Upload
Pi
(ni, ei)
Pi, {K}Si, Siei, {F}K
Cloud Data owner Key manager
Send policy Pi
Return RSA publickey for Pi
Send metadata & encrypted file to cloud
• Data owner randomly chooses (i) K for file F and (ii) Si for policy Pi.
• Things sent to cloud• Pi = policy Pi
• {K}Si = data key K encrypted with Si using symmetric key crypto
• Siej = secret key Si encrypted with ei using public key crypto
• Si is used for policy renewal
• {F}K = file encrypted with data key K using symmetric key crypto
Cache (ni, ei) forfuture use
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File Download
Pi, Siei Rei
SiR
Pi, {K}Si, Siei, {F}K
Cloud Data owner Key manager
Send all backto data owner
Decrypt with di, and return
Send blinded Siei
• Data owner randomly picks a number R, and blinds Siei
with Rei
• It unblinds SiR, and recovers K and F
Unblind Si R
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Policy Renewal
• Main idea: Si re-encrypted into Siem
• {K}Si and {F}K remain unchanged on cloud
Pi, Siei Rei, Pm
SiR, (nm, em)
Pi, Siei
Cloud Data owner Key manager
Send only Pi
and Siei
Decrypt with di, and return
Send blinded Siei
and new policy Pm
Pm, Siem Unblind Si
Reencrypt with em
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Experiments
• What is the performance overhead of FADE?• e.g., metadata, cryptographic operations
• Performance overhead:• Time
• File transmission time• Metadata transmission time• Time for cryptographic operations (e.g., AES, HMAC, key
exchanges)
• Space• Metadata
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File Upload/Download
• Overhead of metadata is less if file size is large• Time for cryptographic operations is small
File upload File download
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Conclusions
• FADE, an overlay cloud storage system with access control and assured deletion
• Cryptographic operations for policy-based file assured deletion
• Implement a FADE prototype atop Amazon S3• FADE is feasible in practice
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Comparison
Wang’s approach FADE
Supported by existing cloud infrastructure No, required new protocol support Yes
Access control policies Yes Yes
Multiple policies combination No Yes
Assured deletion Yes Yes
Implementation Yes Yes
Overhead Low Low
Block update Yes No
Block insertion and appending Yes No
Clients’ responsibilities Low High
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Thank you