1 Qi Li, Tsinghua University Xinwen Zhang and Jean-Pierre Seifert, Samsung Research Hulin Zhong, Lutong Network Secure Mobile Payment via Trusted Computing.

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Qi Li, Tsinghua University

Xinwen Zhang and Jean-Pierre Seifert, Samsung Research

张新文Hulin Zhong, Lutong Network

Secure Mobile Payment via Trusted Computing

This talk does not represent Samsung’s technical view

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Mobile Threats

• Mobile devices become more open and general-purpose

• McAfee's 2008 Mobile Security Report– nearly 14% percent of global mobile users have been directly infected or

have known someone who was infected by a mobile virus– more than 86% of consumers worry about receiving inappropriate or

unsolicited content, fraudulent bill increases, or information loss or theft– more then 70% of users expect mobile operators or device manufacturers

to pre-load mobile security functionality.

• F-secure 2007 mobile threat report– 370 malware by end of 2007– viruses, Trojans, and spyware– User downloaded codes, BT, MMS, MMC card

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Related Work in Samsung

• Secure boot on mobile phone devices– Secure u-boot – Integrity verification of kernel image and read-

only filesystem

• Integrity measurement for mobile phone– IMA – SELinux– TCG MPWG compatible mobile phone platform

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Outline

• Problem Statement• Background• Overview of Secure Payment Scheme• Secure Payment Transactions• Enhanced Payment Schemes• Prototype Implementation and

Evaluation• Conclusion

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Mobile Payment• A typical mobile payment scheme involves three parties: a mobile device, a

merchant, and a financial service provider.

• There are two types of e-payment applications:– Check-like payments require a certain amount of virtual money which is taken

away from the customer before a payment is made.– Cash-like payments require that a customer’s account is involved in each payment

transaction.

• To secure a payment transaction, a trusted third party (TTP) is involved to authenticate and authorize users.

• General security requirements of mobile payments have been well studied in the literature, however, mobile phones face the intrusion of different malware.

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Problem Statement

• The existing embedded operating systems (OS) cannot provide sufficient integrity and isolation protection for the security demands of mobile payment applications.

• While the majority of existing research focuses on secure payment transactions, there is no intensive research on platform integrity protection for secure payments on mobile devices.

• Without trusted mobile devices, the security of payment applications and data cannot be guaranteed at all.

• Existing secure payment schemes fail to provide a platform integrity protection solution for mobile payment transactions.

• The problem how to establish and verify a secure runtime environment of an

e-wallet software was never addressed until now.

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Trusted Computing

• As a key mechanism defined by the TCG, attestation is used to report the measured PCR values to a requestor who needs to know the runtime-state of a platform.– System components validate whether the runtime environment;

– Measurement agent measures the state of the runtime environment;

– Attestation service provides the platform integrity metrics.

• Typically, a trusted boot mechanism is also required for a trusted platform, e.g., with the help of a core root of trust for measurement (CRTM) and the TPM itself.

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Secure Payment Scheme

• We propose a platform integrity protection solution for the whole secure mobile payment process.

• Our architecture consists of five major parties for a complete secure m-payment solution:– Mobile phone: A trusted mobile device consists of a TPM and trusted services

which provide the integrity evidences of the platform.– Software provider: A software provider provides payment applications in a

secure way, such as e-wallet.– Merchant: Merchants not only need to provide the commodities that

customers demand, but also the Point of Sales (POS) devices to authorize customers and guarantee that the payment information is forwarded to the financial service providers.

– Financial service provider: provides user accounts for m-payments and validates the user payment information during the payment transaction processes.

– TC service provider: a trusted third party (TTP) to validate whether a measurement list is non-tampered and the system integrity

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Secure Payment Transactions

• Secure software downloading – For a secure payment scheme, e-wallet applications are essential for m-

payment transactions. In this context an e-wallet runtime environment is also important.

• Secure e-wallet initialization – In order to secure payment transaction processes itself, we also need to

secure the e-wallet initialization process.

• Secure payment transaction – Similarly, we need to evaluate and validate the integrity of the whole

mobile phone before an actual payment process.

• We assume that the key pairs of an AIK should be generated inside the TPM of the mobile phone and the AIK credential should be signed and retrieved from the third trusted party.

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Secure Software Downloading

• The process of application downloading consists of two stages, the first stage is integrity measurement and the second is software downloading.– A measurement request is generated by the application manager, and the

measurement service initiates the respective measurement operation.

• Software runtime environment and e-wallet application downloading, which have similar procedures.

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Secure Downloading Protocol

• Secure Downloading Protocol– The TC service provider verifies the AIK certificate which binds

the verification key of the Quote.– The signatures of the software runtime and the software integrity

are verified before software installation.

TPMAttestation

ServiceMeasurement

AgentApplication

ManagerTC Service

ProviderSoftware Provider

1) Attestation request: {nonce}2) Quote=

Sig{PCR, nonce}AIK

3) Measurement List (ML)

4) {Quote, (ML}5) {Quote, (ML}

6) {Quote, (ML}

6a) determine trusted credential

6b) validate signature

6c) validate ML using PCR

7) Attestation result8) {software| SIg{software}SK_SP}

8a) verify the software provider

8b) verify the software

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E-wallet Initialization

• The e-wallet initialization

aims to generate a key

pair and securely stores

the private part (e.g., account info) for the

m-payment application.

• Seal secrets with TPM

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Secure payment transaction

• Procedures– Similar to the above two

processes, the integrity

measurement mechanism is

also invoked in the process of

secure payment transaction. – Secure Payment Protocol

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Enhanced Payment Schemes

• The efficiency and scalability issues of mobile payment will greatly influence mobile payment performance.– First, in the above scheme, each mobile payment application needs an AIK,

which introduces management cost to the overall mobile computing infrastructure

– Second, in the above scheme the TC service provider is involved in the attestations of every payment transaction.

• We propose two enhanced mobile payment solutions for different optimization requirements. – In the first solution, we leverage the phone number as the device identity to

resolve the credential management problem.– Second, for further optimization, we also reduce the TC service provider

related attestation steps during payment transactions.

• These two enhanced schemes are independent of each other, and they can be jointly used in a real system.

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IBS for Attestation

• In a typical IBS system, there are four basic algorithms: setup algorithm, extract algorithm, sign algorithm and verify algorithm.

• In this scheme, we fully utilize the mobile phone infrastructure and replace in the transaction processes the AIK based public key signature with an IBS algorithm.

• We only replace the signature algorithm and do not change the underlying payment protocols, the enhanced schemes achieves the same security goals.

PKG

Alice

sQIDAMSK,“Alice”

(MK,MSK)1k

MKg

MK

M

sQIDA

sQIDA

UKg

Sign

Bob

acc/rej

MK, “Alice”

VerifyM,σ

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Extended AIK Certificate for Attestation

• In the payment scheme, the financial service provider needs to interact with the TC service provider within every payment transaction, which might be a potential performance bottleneck.

• The core idea behind this scheme is that the integrity of the mobile phone is validated when the TC service provider issues an AIK certificate and the expected integrity values are included within the certificate.

• In summary, compared to the original one, several benefits are achieved by this new scheme: – Flexibility: In this scheme, a financial service provider or a POS terminal can

directly attest a mobile phone on behalf of a TC service provider– Security: The integrity of the mobile platform is in any case validated by

comparing the claimed measurement values to those embedded inside the AIK certificate.

– Performance: A TC service provider is not involved in every payment transaction and a financial service provider can directly attest a mobile phone

TPMAttestation

ServiceMeasurement

AgentM-Payment Application

Financial Provider

1) Attestation request: {nonce}2) Quote=

Sig{PCR, nonce}AIK

3) Measurement List (ML)

4) {Quote, (ML}

6) { User account| Signature

|Quote, (ML}

6a) determine trusted credential

6b) validate signature

6c) validate PCR in credential

Transaction e-receipt}

5) TPM_Unseal(PCR)

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Prototype Overview

• In our prototype, the platform integrity storage is realized by a software TPM. Specifically, Trusted Java is used to provide the TCG Software Stack (TSS).

• Different platforms were developed to act as a mobile device, a financial service provider, a POS terminal, and a TC service provider, respectively.

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Performance Evaluation

• We only evaluated the performance of payment transactions including the integrity attestation operations.

• The measured time includes the time of the TPM operations, the measurement time, the verification time and the overhead.– A whole payment transaction without SSL may cost only 2.70s — even

with 100 concurrent transactions to the same financial service server.

• We similarly evaluated our enhanced payment scheme using an IBS. Similar performance is achieved.

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Related Work

• M-payment security has been studied extensively in the literature. – security requirements of mobile payments– biometric-enabled payment system– solutions considering the restrictions of mobile networks– ……

• Another line of work focuses on securing e-wallets. – A generalization of e-wallets to enable account-based payments.– Ebringer et al. propose a parasitic authentication, thus offering security for

handheld computers– ……

• Molar et al. provide a secure RFID solution with remote attestation. They fully use TC technologies to secure RFID.

• Platform integrity measurement and attestation mechanisms– IBM IMA– Property-based, Semantic-aware, Behavior-based attestation

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Conclusion

• We proposed a secure mobile payment scheme using trusted computing (TC) technology. In our proposed architecture we presented a platform integrity protection solution for mobile payment via NFC.

• Our scheme addresses the unresolved security challenges of mobile payment, including platform integrity verification and user privacy protection.

• In order to improve the efficiency, flexibility and performance of our payment scheme, we proposed two enhanced payment schemes, utilizing an IBS scheme and an attestation cache.

• The experimental results show that our scheme is efficient and effective to achieve the security target.

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Problems and Ongoing Work

• Platform integrity measurement– Existing solution are not practical

• Either trust all components, or trust some untrusted components– Representing of platform integrity measurement

• Static/loadtime measurement only

• Our ongoing work: – Efficient IM and attestation for mobile phone devices– Leverage some unique properties of phone systems and business model– Leverage integrity models: Biba, Clark-Wilson, LOMAC, SEIM, etc

• To reduce measured components• But still preserve the attestation assurance• Via mandatory access control in OS level for information flow monitoring

– Virtualization on mobile devices• Virtualogix, Trango, OpenKernel, etc.

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Thanks

Q&A

[email protected]