Social Networking with
Frientegrity: Privacy and Integrity
with an Untrusted Provider
Prateek Basavaraj
April 9th 2014
Social Networks

Social Networking services require users to trust the service provider with
Confidentiality and Integrity of Data
University of Central Florida
Threats to Confidentiality
 Theft by Hackers
Hacker got access to accounts of
Several prominent members
Source: Federal Trade Commission
 Privacy
Policy and
setting changes
Source: Electronic Frontier Foundation (2010)
 Pressure from
government agencies to
release information on
demand
Source: The wall Street Journal-Tech(2012)
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Threats to Integrity
Server Equivocation
Malicious service presents different clients with the divergent views of system
state
Example: Sina Weibo tried to disguise its censorship of a user posts by hiding them
from user’s followers but still showing them to user
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Online Social Networks are Centralized
Advantages:
Global Accessibility
 Availability
 Convenience
Disadvantages:
Attractive targets for attack by malicious insiders and outsiders
Threat to confidentiality and Integrity of user data
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Frientegrity





Framework for building Social Networking services
Protects the privacy and integrity of users data from malicious
provider
Preserves the availability, reliability and usability benefits of
centralization
Supports social networking features like walls, news feeds,
comment threads and photos
Supports access control mechanisms such as friends, friends of
friends and followers
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Goals of Frientegrity

Broadly Applicable : Must Support features like

Facebook like walls, twitter like feeds
Friend of friend relationships (like facebook) and follower relationships
( like twitter)







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Confidentiality: Frientegrity must ensure that
Only clients of authorized users obtain the necessary encryption keys
Detection of misbehavior: Frientegrity must guarantee that
Clients must be able to detect the misbehavior of the users
Efficient: Frientegrity should be scalable
Access control list changes must be performed in time
Display only most recent updates
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Frientegrity

Provider servers only see encrypted data
 Clients can also collaborate and verify the provider hasn’t corrupted
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Detecting Server Equivocation

Problem: Frientegrity clients digitally sign all the operations
with their users private keys but malicious provider could still
equivocate the history of operations

Solution: Enforce fork* consistency
Clients share information about their individual views of
the history by embedding it in every operation they send
Clients detect equivocation after exchanging two
messages


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Detecting Server Equivocation (Continued)
Alice and Bob detect Equivocation after exchanging two messages
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Frientegrity System Model
Source: Usenix.org
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Frientegrity System Model (Continued)


Bob checks:
Whether the provider has not equivocated about the wall’s
contents

Every operation was created by an authorized user

The provider has not equivocated about the set of authorized
users

ACL is not outdated
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Access Control Lists (ACL)

User’s profile consists of multiple objects like photos, videos
and comments

Frientegrity uses ACL to allow only certain friends to access
the objects

ACLs store user’s pseudonyms and every operation is labeled
with the pseudonym of its creator
ACL – List of Permissions attached to an object
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Access Control Lists (ACL) (Continued)
Frientegrity also uses ACL’s to store the key material with
which authorized users can decrypt the operations on walls
and encrypt new ones
 Social Networks ACLs are large
 ACL modifications and associated rekeying must be efficient
ACL Rollbacks: Situation where malicious provider give Bob an
outdated ACL
Solution: Operations in Alice’s wall are annotated with
dependencies on Alice‘s ACL history

particular operation in one object happened after a particular
operation in another object
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Frientegrity Object Representation
Objects are represented as history trees
Operations are stored in the leaves
Each internal node stores the hash of the sub tree below it
Hash of the root covers the tree entire contents
New leaves can be added to the right side of the tree
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Verifying Objects in Frientegrity
Bob’s op
Clients collaborate to verify the history
Charlie’s op
Alice’s op
0
8
4
C0
C4
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11
C8
15
C11
Tolerating Malicious users in Frientegrity
Tolerate up to f malicious users
Bob’s ops
Charlie’s ops
Alice’s ops
op15
op9
C11
C9
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Access Control
Raj
Thomas
Bob
Alice
Charlie
John
Every node contains hash of the children and root node is signed by Alice
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Efficient Key Distribution
Ek3(k1) || Ek4(k1)
KEY GRAPHS
k0=kalice_friend
Raj k0
Bob k1
Alice k3
Charlie k4
Thomas k2
John k5
Advantage : Allows any user who can decrypt the
particular node can follow the path of decryption
upto the root and obtain the root key to encrypt
the data
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Unfriend and Add friend in Frientegrity
Alice ACL
Raj k0
Raj k0’
Bob k1’
Alice k3
Charlie k4
Thomas k2
John k5
Bob k1
Thomas k2
Rahul k6 Alice k3 Charlie k4 John k5
Unfriend: Update k0’ and k1’
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Raju k7
Add friend: Update node
Ek5(k2)|| Ek7(k2)
Implementation

Approximately 4700 lines of Java code

Protobuf-socket-rpc library for network communication

2048- bit RSA spliced signatures – To sign and verify
operations in batch

Simulate basic Facebook features (user has wall and ACL)
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Experimental Evaluation
Single-Object Read and Write Latency
Frientegrity
HashChain
Verifying an object with history size of 25K operations would take approximately
10s in hash chain and 6s in Frientegrity
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Experimental Evaluation (Continued)
Latency of ACL modifications:
Latency of Fetching a News Feed:
Fetching wall posts from 500 friends would require approximately 1.8 seconds
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Strengths and Weakness
Strengths:
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Frientegrity provides the much needed framework for privacy and integrity
in social networking applications
Clients collaborate to defend against equivocation
Scalable and verifiable access control and key distribution
Benefit from Centralization
Weakness:

Still uses untrusted third party infrastructure
Future Work

Development of business model that can support privacy-preserving
services hosted with third party providers
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Conclusion

Provides data confidentiality and integrity

Efficient, scalable and usable

Detects server equivocation

Efficient access control

Provides satisfactory response times
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References

Social Networking with Frientegrity: Privacy and Integrity
with an Untrusted Provider – Arial J Feldman, Aaron Blankstein,
Michael J Freedman and Edward W. Felten Princeton University
21st Usenix Security Symposium

Facebook Inc, Anatomy of Facebook
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THANK YOU
QUESTIONS?
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