towards user-friendly credential transfer on open ... · 1 kari kostiainen, n. asokan nokia...
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Kari Kostiainen, N. Asokan Nokia Research Center
Alexandra Afanasyeva SUAI
ACNS 2011
Towards User-Friendly Credential Transfer on Open Credential Platforms
© 2011 Nokia Research Center
© 2011 Nokia Research Center 2
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Trusted execution environment (TrEE)
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Credential transfer
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Outline
1. Credential transfer problem
2. Credential transfer protocol
3. Analysis
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Credential transfer problem
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Closed provisioning
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Control point
Service provider Service provider Service provider
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Open provisioning
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User authentication
User authentication
User authentication
Copyable Non-transferable Non-transferable
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Late user binding
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Device certificate
Enc(credentials)
User binding User binding
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Temporal disconnection
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Requirements
• Usability −No additional user interaction
• Security −Credential secrecy
−“Credential fidelity”
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Credential transfer protocol
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Protocol overview
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HSM Provisioner (P)
Source device (S)
OS
TrEE
Target device (T)
OS
TrEE
PKTS/SKTS, CertTS
PKT/SKT, CertT
PKS/SKS, CertS
Trusted Server (TS)
OS
1. User identity installation
2. Provisioning and user binding
3. Credential backup and “identity verification delegation”
4. User identity installation
5. Identity verification, credential recovery and “provisioning delegation”
6. Automatic re-provisioning
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1. User identity installation
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PwdS
SealedPwdS
SealedPwdS Seal(PwdS)
PwdS
Store SealedPwdS
User Source OS Source TrEE
1. Trust on first use 2. Typical device login
ProvCred, SealedPwdS
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2. Credential provisioning
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ProvCred
CertS + user auth.
SealedCred
Verify CertS and extract PKS
Map Cred to PKS
ProvCred Enc(PKS, Cred || policy)
Cred || policy Dec(SK, ProvCred) PwdS Unseal(SealedPwdS) SealedCred Seal(Cred || policy || PwdS)
Store SealedCred
Provisioner Source OS Source TrEE
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3. Credential backup to server
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Source OS Source TrEE Trusted Server (TS)
CertS, EncCred / SDT
EncCred / SDT
CertTS, SealedCred
Verify CertTS and extract PKTS Cred || policy || PwdS Unseal(SealedCred)
Copyable: EncCred Enc(PKTS, Cred || PwdS) Non-transferable: SDT Sign(SKS, PKTS) || Enc(PKTS, PwdS)
CertTS
Store CertS and EncCred / SDT
CertS, EncCred / DT EncCred
SealedPwdT
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5. Credential recovery
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Trusted Server (TS) Target TrEE Target OS
PwdToken PwdToken, CertT
Verify CertT and extract PKT
PwdT Dec(SKTS, PwdToken) Copyable: Cred || PwdS Dec(SKTS, EncCred) Verify PwdT = PwdS
EncCred End(PKT, Cred || PwdT) Non-transferable: Extract PwdS from SDT Verify PwdT = PwdS
DT Sign(SKTS, PKT) || Sign(SKS, PKTS)
PwdT Unseal(SealedPwdT) PwdToken Enc(PKTS, PwdT)
Install EncCred
User identity installation
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6. Credential re-provisioning
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Target TrEE Target OS Provisioner
CertT, CertS, CertTS, DT
Verify Certs Verify signatures on DT
Find Cred for PKS
ProvCred Enc(PKT, Cred || policy)
ProvCred
ProvCred
Install ProvCred
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Analysis
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Analysis
• Usability −Reusing typical device login
• Credential secrecy −Common public key mechanism
−Trusted server (HSM)
• Credential fidelity −User identity password
−Brute force (throttling)
−Phishing (separate password)
−Password change (“trusted UI” or secure connection to server)
• Protocol validated with AVISPA tool 20 © 2011 Nokia Research Center
Summary
• Credential transfer challenging −Open provisioning
−Late user identity binding
−Temporal disconnection
• Server-assisted credential transfer protocol −Can be implemented using existing devices
21 © 2011 Nokia Research Center