User-centric Security Models Manuel Ziegler Advisor: Heiko - - PowerPoint PPT Presentation

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Technische Universität München – Chair for Network Architectures and Services

User-centric Security Models

Manuel Ziegler

Advisor: Heiko Niedermayer Seminar Future Internet SS 2015 Chair for Network Architectures and Services Department for Computer Science Technische Universität München

April 10, 2015

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Technische Universität München – Chair for Network Architectures and Services

Outline

1)

Introduction

2)

Direct trust and well known decentralized trust models

3)

Trust Establishment

4)

Trust Decisions

5)

Trust Metrics

6)

Conclusion

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Technische Universität München – Chair for Network Architectures and Services

Introduction

Centralized CA models:

 TLS, S/MIME  Tree based certificate chain  Certificate Authority tells you, who to trust  CAs are paid for signing certificates

root certificate (CA) TLS certificate example.com TLS certificate example.de S/MIME certificate John Doe

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Technische Universität München – Chair for Network Architectures and Services

Introduction

The user-centric approach:

 Not just tree alike trust chains  User decides by his own, who to trust  Difficult decision making for less experienced users  When used correctly: Better trustworthiness than CA based Trust

Alice Bob Carol Dan Chuck

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Technische Universität München – Chair for Network Architectures and Services

Direct and well known decentralized Trust Models

Direct trust model:

 Personal meeting between users required  Does not scale  Can be combined with decentralized trust models  Some applications provide the direct trust model retrospectively:

– TextSecure – PGP

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Technische Universität München – Chair for Network Architectures and Services

Direct and well known decentralized Trust Models

OpenPGP / GnuPG:

 Public key servers – everybody can modify entries  Trust Signatures  Privacy Problem: Social environment can be determined from

trust signatures

 Often Trust is established with the help of CA models

(Fingerprint on TLS encrypted Website) SSH:

 Local key database  Trust on first connection  Similar Concept: Certificate Pinning in Web browsers

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Technische Universität München – Chair for Network Architectures and Services

Trust Establishment

Trust Chains:

 Usually given as graph structures  Rating of trust relationships possible  Trust Relationships can be derived from a trust chain

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Technische Universität München – Chair for Network Architectures and Services

Trust Establishment

Trust-Rated Authentication in domain structured networks:

 Trust Token with meta information is obtained from a Domain

Authentication Server (Holz, et al. 2008 [1])

– Key exchange information – Known frauds – Previous contacts

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Technische Universität München – Chair for Network Architectures and Services

Trust Establishment

Trust Establishment with the help of a councelor:

 PGP

– Alice obtains the certificate from Bob through Carol (signed) – Bob obtains the certificate from Alice through Carol (signed)

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Technische Universität München – Chair for Network Architectures and Services

Trust Establishment

Trust Establishment with the help of a councelor:

 Trust Exchange Protocol (Kinkelin, et al. 2014 [2])

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Technische Universität München – Chair for Network Architectures and Services

Trust Decissions

Trustworthiness and reputation:

 Reputation = Users Assessment of another user's ability to

validate the identity of other users (Kinkelin, et al. 2014 [2])

 Often Coupled with trustworthiness

Supporting the decision making process:

 Collect Information  Categorize  Evaluate  Display  Examples: Web of Trust Browser Plugin, OTO – Online Trust

Oracle (Kim, et al. 2012 [3])

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Technische Universität München – Chair for Network Architectures and Services

Trust Decissions

Source: Kim, et al. 2012 [3]

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Technische Universität München – Chair for Network Architectures and Services

Trust Metrics

P1=A→B→E P2=A→C→E P3=A→D→F→E

T =

∑

i=1 n

∏

j=1 k

ei, j n T=0,8⋅0,3+0,6⋅0,7+0,9⋅0,8⋅0,9 3 T=0,24+0,42+0,648 3 T=0,436

P=e1⋅...⋅ek

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Technische Universität München – Chair for Network Architectures and Services

Trust Metrics

ILRI=

∑

C∈Councelors

ILCI⋅ RLRC RLmax ⋅ILRC ILmax ∣Counselors∣ ⋅d

Kinkelin, et al. 2014 [2] IL = Identification Level RL = Reputation Level

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Technische Universität München – Chair for Network Architectures and Services

Conclusion

 Many different decentralized trust models  Few user supporting trust decision systems  Decentralized Trust models require expert knowledge  Most global infrastructure based on CA based models

→ Still a lot work to do

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Technische Universität München – Chair for Network Architectures and Services

References

[1] R. Holz, H. Niedermayer, P. Hauck, and G. Carle: Trust rated authentication for domain structured distributed systems, Public Key Infrastructure – 5th European PKI Workshop: Theory and Practice, 2008 [2] H. Kinkelin, H. Niedermayer, S. Mittelberger, and G. Carle: Human-centric and privacy protecting trust establishment over the internet, CENTRIC: The Seventh International Conference

• n Advances in Human-oriented and Personalized Mechanisms,

Technologies, and Services, 2014 [3] T. H.-J. Kim, P. Gupta, J. Han, E. Owusu, J. Hong, A. Perrig, and Debin: OTO: Online Trust Oracle for user-centric trust establishment, ACM conference on Computer and communications security, 2012

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Technische Universität München – Chair for Network Architectures and Services

Questions