Authentication and Integrity in Outsourced Databases

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Authentication and Integrity in Outsourced
Databases

• Kanaka Rajanala

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What is Outsourced Database

• Organizations outsource their data management
  needs to an external provider.
• The service provider hosts client database and
  offers mechanisms.
• Create databases
• Updating
• Storing
• Accessing (querying)

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Advantages of ODB

• The organizations can concentrate on their core
  tasks and operate their business applications via
  Internet.
• Dont worry about
• Deployment, instillation, maintenance ,upgrades.
• Hire, train/retain people.

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Challenges

• Overall performance
• Scalability
• Usability

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Challenges

• Privacy/Security
• Protection of outsourced data from intruders and
  attacks.
• Protecting clients from misuse of data by service
  providers.
• Ensuring integrityprivacycompleteness of query
  replies.

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Goal

• This paper investigate techniques to help ODB
  client authenticate the origin and verify the
  integrity of data returned by the service
  provider in response to a posed query.

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System Model

• ODB is an example of Client Server model.
• Types of ODB
• Unified Client Model
• Multi Querier Model
• Multi Owner Model

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1. Unified Owner Scenario
Server Site
Server
Data Deposit Queries
Encrypted User Database
A single entity creates, queries, manipulates
the database.
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2. Multi-Querier Scenario
Server Site
Data Deposit queries
Server
Encrypted User Database
Data Queries
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3. Multi-Owner Scenario
Server Site
Server
Encrypted User Database
Data Deposit queries
Data Queries
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Why do we need Integrity

• In some occasions where we may not want secrecy
  but want integrity
• Every one is allowed to read a message
• But no one is allowed to modify it.

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Why do we need Authentication

• To authenticate the source of data.
• The main goal is to assure ODB clients that the
  data they receive from the server has not be
  tampered from an external adversary or the server
  itself.

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Granularity of Integrity

• Table level-impractical for large tables.
• Column level-very expensive for the owner in
  terms of computation.
• Optimal is to provide integrity at row level.

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Overhead Factors and Desired Features

• Querier computation
• Querier bandwidth
• Server computation
• Owner computation
• Server storage

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MACs or Signatures

• With MAC client can ask server to store record
  along with MAC.
• Works for Unified Client model where owner and
  querier are same.
• Cannot be worked with other models
• MAC key to be shared between all owners and
  queriers.
• Non repudiation of queries cannot be achieved.

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Standard RSA
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Condensed RSA

• Server
• Selects records matching posed query
• Multiplies corresponding RSA signatures
• Returns single signature to querier

Server
Querier
Given t record signatures s1, s2 st ,
compute combined signature s1,t ?si mod n
Send s1,t to the querier
Given t messages m1,m2 mt and s1,t verify
combined signature (s1,t)e ? ? h(mi) (mod
n)
s1,t
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Condensed RSA

• Reduced querier computation costs
• Querier performs (t-1) mult-s and a one
  exponentiation
• Constant bandwidth overhead
• Querier receives a single RSA signature
• As secure as batch RSA (with FDH)
• Not efficient for Multi-Owner model

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Batch Verification of RSA Signatures

• Batching useful when many signature
  verifications need to be performed simultaneously
• Reduces computational overhead
• By reducing the total number of modular
  exponentiations
• Fast screening of RSA signatures
• Given a batch instance of signatures s1, s2
  st on distinct messages m1, m2 mt

where h() is a full domain hash function
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Fast Screening

• Reduces (somewhat) querier computation but not
  bandwidth overhead
• Individual signatures are sent to the querier for
  verification
• Bandwidth overhead can be overwhelming
• Consider weak (anemic) queriers
• Query reply can have thousands of records
• Each RSA signature is at least 1024 bits!

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Cost Comparisons
1. Querier computation
Condensed RSA Batch DSA
Sign 1 signature 6.82 3.82
Verify 1 signature t 1000 sigs, k1 signer t 100 sigs, k10 signers t 1000 sigs, k 10 signers 0.16 44.12 45.16 441.1 8.52 1623.59 1655.86 16203.5
Parameters For RSA n 1024 For DSA p
1024 and q 160