A Persistent Public Watermarking of Relational Databases Raju Halder, Agostino Cortesi Department of Computer Science Universita` Ca’ Foscari Venezia, Italy {halder, cortesi}@unive.it

ICISS’2010, Gujrat, India

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Outline 1

Introduction to Database Watermarking

2

Why Public Watermarking?

3

Why Persistent Watermarking?

4

Invariants of Database States

5

Abstract Databases

6

Way to improve existing schemes in terms of persistency

7

Proposed Scheme Public Watermarking Private Watermarking

8

Time and Space Complexity

9

Discussions

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Introduction Information systems are shared by many people around the world. - Example: “Database as a Service model” Content of the databases faces serious challenges: - Illegal redistribution, ownership claims, forgery, theft, etc. Encryption/Decryption? so restrictive. Alternative way is Digital watermarking. Digital watermarking embeds some kind of information into the underlying data of the databases. Purpose: ownership proof, traitor tracing, tamper detection, localization, etc.

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Introduction Key (K) Original Database

Watermarking

Watermarked Database

Signature S Figure: Watermarking Phase

Key (K) Suspicious Database

Watermark Verification

Signature S’

Compare

Claim as true or false

Original Signature S Figure: Watermark Verification Phase

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Why Public Watermarking? Private Watermarking: Based on some secret parameters. Only authorized people who knows these secret parameters (e.g. DB owners) are able to verify the watermark. Suffers from disclosure of secret parameters to dishonest people once the watermark is verified in presence of the public. Public Watermarking: No secret parameter is needed during verification. Any end-user can perform the verification as many times as necessary. Robustness and fragileness are burning issues. One Example of Use: To ensure correctness and originality of sensitive data, say currency exchange rates or stock prices, by all customers. Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

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Why Persistent Watermarking?

Existing watermarking schemes rely on the content of the database. Benign Updates or any intensional processing may change database content, and may damage/distort the existing watermark. Notion of persistency comes into the context.

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Persistent Watermarking

Let hdB, Qi be a database model, where Q is the set of queries bounded with the database dB. Watermark W is embedded in initial state d0 .

Definition (Persistent Watermark) Watermark W embedded in the state d0 is called persistent w.r.t. Q if ∀ i ∈ [2 . . . n] : verify(d0 , W ) = verify(di , W ) where “verify(d, W )” is a boolean function such that probability of “verify(d, W ) = true” is negligible when W , watermark embedded in d.

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Invariants of Database States

Static versus Non-static Database States: Static part: data cells are not affected by processing of queries in Q. Non-static part: data cells may change under processing of queries in Q.

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

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Invariants of Database States Semantics-based Properties: Intra-cell (IC) property: - Represents specific properties of individual cells. - Ex: Integer attribute values x represented by Interval [a, b], a ≤ x ≤ b. Intra-tuple (IT) property: - Property based on the inter-relation between two or more attribute values. - Represented by relational abstract domain (e.g. domain of octagons). - Ex: Inter-relation between basic and gross salary. Intra-attribute among-tuples (IA) property: - Property extracted from the set of tuples. - Represented by relational or non-relational abstract domain. - Ex: # male employee = # female employee + 1. - Ex: # employees ≥ 3.

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Abstract Databases Data values are replaced by abstract values from abstract domains representing specific properties of interest. Although concrete values change, their abstract values representing properties do not change under processing of queries in Q. eID E001 E002 E003 E004 E005

eID] E001 E002 E003 E004 E005

Name Bob Alice Matteo Tom Marry

Name] Bob Alice Matteo Tom Marry

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

The concrete table emp Basic Sal (euro) Gross Sal (euro) 1000 1900 900 1685 1200 2270 600 1190 1350 2542.5 The abstract table emp ] Basic Sal] (euro) Gross Sal] (euro) [1000, 1300] [1900, 2470] [900, 1170] [1685, 2191] [1200, 1560] [2270, 2951] [600, 780] [1190, 1547] [1350, 1755] [2543, 3305]

A Persistent Public Watermarking of Relational Databases

Age 48 29 58 30 55

Age] 48 29 58 30 55

DNo 2 1 2 2 1

DNo] 2 1 2 2 1

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Improvement in terms of persistency

Roles of Invariants and Abstract Databases in Persistency: Invariants: Static Part of DB state and Semantics-based properties. Partial Abstract Database: Obtained by abstracting only non-static part. Exploit these invariants and abstract databases to obtain a persistent watermarking.

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Outline 1

Introduction to Database Watermarking

2

Why Public Watermarking?

3

Why Persistent Watermarking?

4

Invariants of Database States

5

Abstract Databases

6

Way to improve existing schemes in terms of persistency

7

Proposed Scheme Public Watermarking Private Watermarking

8

Time and Space Complexity

9

Discussions

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Public watermarking Performed by: Database Owner Original Database DB(PK,A0, . . . , A β − 1 ) in state d associated with Q

Signature S Parameter

GenPublicKey

Performed by: End-Users Suspicious Database DB(PK,A0, . . . , A β − 1 ) in state d’ associated with Q

Parameter ξ

PublicVerify

ξ An intermediate table in binary form B’(PK,a0, . . . , ap-1)

Public Key B(PK,b0, . . . , bp-1) in binary form

ExtractSig Signature S’ MatchSig

p≤β

Original Signature S

Signature Verification Claim as True or False

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

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Public watermarking (Performed by Owner) eID

Name

Basic_Sal

Gross_Sal

Age

Dno

E002

Alice

900

1685

29

1

-

-

-

-

-

-

Persistency

< E002; Alice; - ; - ; 29; 1 > Fragileness

S=”RAJU”= 0101001…101 |S| m= = 31 =11 3 | Astatic | S=(S1)(S2)…(S10)=(010)(100)…(101)

h =HASH(E002||Alice||29||1, 3)=001 i = PRSG(E002)%11 = 2 W =h ⊗ S2= 001 ⊗ 100= 101

Signature embedding

K’alice’=HASH(E002|| Alice)% ξ =2 K’29’=HASH(E002|| 29)% ξ =3 K’1’=HASH(E002|| 1)% ξ =1

Assuming Q increases only Basic and Gross Salaries of employees!!

Robustness

2nd MSB of ‘Alice’ ⊗ W[0]= 0 ⊗ 1=1 3rd MSB of ‘29’ ⊗ W[1]=1 ⊗ 0=1 1st MSB of ‘1’ ⊗ W[2]= 1 ⊗ 1=0

ID

b0

E002

1

b1 1

b2 0

-

-

-

-

< E002; 1; 1; 0;>

Public Key Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Public watermarking (Performed by End-Users) eID

Name

Basic_Sal

Gross_Sal

Age

Dno

E002

Alice

900

1685

29

1

-

-

-

-

-

-

< E002; Alice; - ; - ; 29; 1 > Public Key ID

b0

E002

1

b1 1

b2 0

-

-

-

-

h =HASH(E002||Alice||29||1, 3)=001

Public Key K’alice’=HASH(E002|| Alice)% ξ =2 K’29’=HASH(E002|| 29)% ξ =3 K’1’=HASH(E002|| 1)% ξ =1 2nd MSB of ‘Alice’ ⊗ h[0]= 0 ⊗ 0=0 3rd MSB of ‘29’ ⊗ h[1]=1 ⊗ 0=1 1st MSB of ‘1’ ⊗ h[2]= 1 ⊗ 1=0

b0 ⊗ a0= 1 ⊗ 0=1 b0 ⊗ a0= 1 ⊗ 1=0 b0 ⊗ a0= 0 ⊗ 0=0

< E002; 0; 1; 0;>

S2 ==100 Signature S=S1S2. . . .S10

ID E002

a0 0

a1 1

a2 0

-

-

-

-

Intermediate Binary Table Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

ICISS’2010

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Outline 1

Introduction to Database Watermarking

2

Why Public Watermarking?

3

Why Persistent Watermarking?

4

Invariants of Database States

5

Abstract Databases

6

Way to improve existing schemes in terms of persistency

7

Proposed Scheme Public Watermarking Private Watermarking

8

Time and Space Complexity

9

Discussions

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

ICISS’2010

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Private Watermarking (Performed by Owner) Q = increase the basic and gross salary of the employees by at most 30%

PK

Stable part

Unstable part

Abstract Tuple Persistency

< E002; Alice; [900, 1170]; [1685, 2191]; 29; 1 > Randomize based on Pseudorandom Seq. Generator based on tuples values’ and secret key

Robustness

Intra-cell Property (ICdQ) : Basic Sal: [900, 1170] Gross Sal: [1685, 2191]

Encoded by k1

< E002; [1685, 2191]; 1; 29; [900, 1170] ; Alice > Prevent Value Modification Attacks

Extract MSB

Intra-tuple Property (ITdQ) :

Gross Sal ≥

< E002; 0; 1; 1; 0; 1 >

165 × BasicSal +200 100

Encoded by k1 Append semantics-based Properties < E002; 0; 1; 1; 0; 1; k1; k2; k3 >

Intra-attribute among-tuples Property (IAdQ) : “The number of employees in every department is more than 2” represented by [3;+ ∞ ]

Encoded by k3 Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

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Time and Space Complexity

η= total number of tuples in a database state. µ = complexity of the abstraction operation applied on each tuple. Public Key Generation and Verification: - Time complexity: O(η) - Space complexity: O(η) Private Watermark Generation and Verification: - Time complexity: O(η × µ) - Space complexity: O(η)

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Discussions and Conclusions

Do not restrict to any particular data type of the attributes. Blind and Distortion-free. Preserve Persistency, Fragileness, and Robustness. Watermark verification algorithms are deterministic in both cases. No need of recomputation when tuples are updated by the queries associated with the database. We strictly improve the scheme of Li and Deng [2].

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

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References Rakesh Agrawal, Peter J. Haas, and Jerry Kiernan, Watermarking relational data: framework, algorithms and analysis. The VLDB Journal, vol. 12, no. 2, pp. 157-169, 2003. Yingjiu Li and Robert Huijie Deng, Publicly verifiable ownership protection for relational databases. In Proceedings of the 2006 ACM Symposium on Information, computer and communications security (ASIACCS ’06), Taipei, Taiwan: ACM Press, 2006, pp. 78-89. Raju Halder and Agostino Cortesi, Persistent watermarking of relational databases. In Proceedings of the IEEE International Conference on Advances in Communication, Network, and Computing (CNC 2010), Calicut, India: IEEE CS, 2010, pp. 46-52. Raju Halder and Agostino Cortesi, Abstract interpretation for sound approximation of database query languages. In Proceedings of the IEEE 7th International Conference on INFOrmatics and Systems (INFOS ’2010), Advances in Data Engineering and Management Track, Cairo, Egypt: IEEE Press, 2010, pp. 53-59.

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

A Persistent Public Watermarking of Relational Databases

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Thank you for your attention !

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

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Suggestions Please !!!!

Raju Halder, Agostino Cortesi (Ca’ Foscari Univ.)

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