Tokenisation and format preserving encryption,

| 08-09-2011 | Cauchie stéphane
Carte & Identification 2011
08 Septembre 2011
Transactional services. Powering progress © Confidential
1
Tokenization
Format Preserving Encryption
A Case study
Cartes & Identification 2011

Summary
2
What is Tokenization in two words
Deﬁnition & Functionalities
Use cases
How does it work ?
Random Token System
Conclusion

What is tokenization in two words [DEFINITION]
▶ Deﬁnition
– Tokenization is a process of replacing sensitive data by non sensitive ones
(tokens) with respect of the following properties:
• Tokens bears enough information to be useful (e.g. The entity manipuling
token can accomplish transaction as it was the sensitive data).
• Tokens does not compromise security
– Tokenization system tries to minimize the integration impact on existing
infrastructure
▶ Who offer such service
3

What is tokenization in two words [FUNCTIONALITIES]
▶ Function description of a Tokenization system
– Conversion (Convert sensitive data into a token and vice versa)
– Conversion policy (Format deﬁnition, Mode of operation)
– Communication Canal : Authentication, Integrity, Conﬁdentiality
4
Tokenization
System
External
System

What is tokenization in two words [USE-CASES]
▶ Focusing on payment (but not limited to)
– Context :
• Sensitive data : PAN,…
• PCI compliancy
– Use cases
• MOTO
• Face2Face
5
CardHolder
AcquirerIssuer
Acceptor

– Context :
• PCI compliancy
– Use cases
• MOTO
• Proximity payment
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CardHolder
AcquirerIssuer
Acceptor
E2E-Encryption

– Context :
• PCI compliancy
– Use cases
• MOTO
7
CardHolder
AcquirerIssuer
Acceptor
Secure MOTO

– Context :
• PCI compliancy
– Use cases
• MOTO
8
CardHolder
AcquirerIssuer
Acceptor
Process
transaction

Summary
9
Use cases
How does it work ?
Random Token System
Conclusion

Tokenization and Format Preserving Encryption: A Case Study
▶PCI-DSS(Payment Card Industry Data Security Standard) :
• Security requirements for entities processing cards data
(processing, transmission and storage)
▶Objectives:
• Reduce PCI evaluation perimeter
• Choose a suitable algorithm that tokenize a PAN
▶Constraints:
• The algorithm must be collision free
• In a certain mode the algorithm must be “not reversible”
• In certain mode the algorithm must not takes secret parameters
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How does it works ? [Objectives-Constraints]

How does it works [RandomToken]
▶ Random Token
– Card data are
• ciphered (classic algorithms)
• stored in a database
– System generate an associated token
• Format respect
• Checks for no Collision
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Summary
12
Use cases
How does it work ?
Random Token System
Conclusion

▶ FPE : Format Preserving Encryption.
▶ Introduced by Brightwell [BS97]
o Encryption scheme with
o format preserving property
▶ Format deﬁnition is a key point
– Follow PCI guidelines :
• you have to differentiate a Token from a PAN
▶ NIST is considering 3 FPE algorithms
▶ Applications :
• Security Social Number
• Credit Card Number
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How does it works [FPE based tokenization]
First introduction of Format Preserving
Encryption [BS97]

▶ NIST is considering 3 FPE algorithms
• FFX [FFX10]
• BPS [BPS10]
• FCEM [FCEM10]
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How does it works [FPE based tokenization]
FFX BPS
FCEM

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▶ Feistel
o Inventé par Horst Feistel .
o Round notion
o Input are split in 2
o F : cipher function
o Secret key K
o Key Derivation algorithm
o During a round
 Ai+1 = Bi
 Bi+1 = Ai Fki(Bi)
o Example
 DES : 16 tours.
+
How does it works [Cryptographic-Approach]

Feature FFX BPS FCEM
Feistel based Yes Yes No
#Rounds 12 8 2
Cipher function AES AES/TDES/SHA AES
#Function is used 12 8 8
Reversibility Yes Yes Yes
Tweak Yes Yes No
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How does it works [Cryptographic-Approach]
▶ Cryptographic notions
– Tweak Notion : Add variability in cryptographic schemes
– Patarin attack : Differentiate ciphertext from random string

Feature Random Token FPE
Multi Site Difficult Medium
Key deployment Medium Hard
Format preserving Easy Easy
Performance Low Fast
Token/Data link No (except in DB) Algorithm
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How does it works [Analysis]

Summary
18
Use cases
How does it work ?
Random Token System
Conclusion

Conclusion [VISION]
▶ Which choice ?
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CardHolder
AcquirerIssuer
Acceptor
Secure MOTO
Process
transaction
FPE
RTS
E2E-Encryption
FPE FPE

▶ Tokenization in payment context
 It allows the reduction of PCI audit perimeter in a payment application
 Waiting for NIST approval.
▶ Depending on use case:
 Random Tokenization:
 In case of internal processing
 FPE based Tokenzaton
 In case of multi site,
 In case of multi-party protocols
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Conclusion []

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are registered trademarks of Atos SA. August 2011
© 2011 Atos. Conﬁdential information owned by Atos, to be used by the recipient only. This document, or any part of it,
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© Conﬁdential
Questions ?
References Title
[BS97] Brigthwell, Michael & Smith
Using datatype preserving encryption to enhance data warehouse security.
20th National Information Systems Security Conference, NIST, 1997.
[FFX10] Bellare M, Rogaway P & Spies T
The FFX Mode of Operation for Format preserving Encryption. 2010.
[BPS10] Brier E, Peyrin T & Stern J
BPS : a format Preserving Encryption Proposal. Ingenico, 2010.
[FCEM10] Ulf T Matsson
Format preserving Encryption Using Datatype preserving Encryption. 2010.
[SEC2] Certicom Research. SEC2 : Recommended Elliptic Curve Domain Parameters. 2000.
[BSGS] D. Shanks. Five number-theoretic algorithms. Proceeding of the second Manitoba
Conference on Numerical Mathematics. 1975.
[RHO] J.M. Pollard. A monte carlo method for factorization. 1978.
[CI] Pierrick Gaudry. Algorithmiques des courbes algébriques pour la cryptologie. 2008
[PCI] Scoping SIG, Tokenization Tasforce, PCI Security Standards Council. PIC-DSS. 2011

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BPS
Survey on FPE

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▶ BPS :
▶ Autor: Brier E, Peyrin T & Stern J.
▶ Published in 2010.
▶ BPS : "a Format Preserving Encryption

Proposal ".
▶ Features:
• 8 round.
• Tweak of 64 bits split in 2 sub tweak
o TL et TR
• F : AES or one way function.
• K : secret key
• reversible.
• Patarin resistant.
Survey on FPE

▶
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Survey on FPE

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FFX
Survey on FPE

▶ FFX :
▶ Autors : Bellare M, Rogaway P & Spies T.
▶ Published in 2009 and 2010.
▶ FFX : "Format Preserving Feistel-based Encryption"
▶ Features:
• 12 round,
• 64 bits tweak,
• FK : AES-128 or one-way function
• K : secret key
• reversible
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Survey on FPE

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FCEM
Survey on FPE

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▶ Autor :Ulf T Matsson.
▶ Published in 2009.
▶ FCEM : "Format Controlling Encryption Mode".
▶ Features:
• 8 steps
o Index Value Data
o Encryption of Left
o Encryption of Right
o Scrambled
o Rippled Left to Right
o Rippled Right to Left
o Encryption and Update
o The last transformation
• F : AES-128
• K : secret key
• reversible
Survey on FPE

▶ Index Value data :
• Rewriting input as hexa values.
• Example:
o X : 1122334455667788
o Index Value data : 01010202030304040505060607070808
▶ Encryption of Left :
• left part encryption
• Example :
o Index Value data : 01010202030304040505060607070808
o Sortie de FK: 00C01F49D0C2C050188D8FDFADCDF846
o RightUpdate : 0507070905010008
▶ Encryption of Right :
• Same idea
• We get LeftUpdate : 0101080503060303
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Survey on FPE

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▶ Scrambled :
• Concat LeftUpdate and RightUpdate .
• Example:
o CipherScrambled : 01010805030603030507070905010008
▶ RippledLeftToRight :
• Scrambled modifying by :
o CipherScrambled : 01010805030603030507070905010008
o 01 ⊕ 01 = (0 × 16) + 1 + (0 × 16) + 1 = 02 ≡ 02 (mod10).
o RippledLeftToRight = 0102
o RippledLeftToRight = 01020005080407000503090803040402
▶ RippledRightToLeft :
• Same idea
• RippledLeftToRight = 04030101060804070702000103000602
Survey on FPE

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▶ Encryption and Modular Sum :
• RippledLeftToRight : 04030101060804070702000103000602
Survey on FPE

Tokenisation and format preserving encryption,

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