Pervasive Computing and Communication Security (PerSec 2006) March 13th, 2006 Florina Almenárez, Andrés Marín, Daniel Díaz, Juan Sánchez DEVELOPING A MODEL FOR TRUST MANAGEMENT IN PERVASIVE DEVICES

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Outline Motivation Related Work PTM: Pervasive Trust Management Model ○Requirements ○Description ○Mathematical Trust Evolution Model ○Probabilistic Trust Evolution Model Component-based PTM Implementation Conclusions

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Motivation Pervasive Computing ○Open and dynamic environments (zoo, airports, shopping mall) ○Multitude of heterogeneous devices with communication, computing and storage capabilities  Pervasive devices TRUST role in establishing new relations ○Secure communication protocols (SSL, IPSec, DNSSEC, …) work well in fixed networks  traditional PKI  Problems to work when trust relationships are not preconfigured ○Some management mechanisms for ad hoc networks  routing

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Related Work Previous works ○1994: Marsh, Beth ○1997: Abdul-Rahman ○1998: Jøsang ○1999: KeyNote, SPKI/SDSI (Access control infrastructures) ○2001: Poblano Recent works ○2002 – 2004: SECURE (IST Project)  Trinity College Dublin ○2000 – 2010: Terminodes  NCCR (ad hoc networks) ○2003 – : SULTAN  Imperial College ○2004 – 2006: UBISEC  Siemens –Problems: complexity, distrust modelling, trust evolution

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Requirements Autonomous  Independence on central server or previous configuration ○to participate in ad hoc networks and peer-to-peer application Dynamic  evolution, context adaptation Simple  minimize human intervention and resource consumption Secure  protect resources from malicious entities ○to make suitable decisions despite the uncertainty Cooperative  benefit from common knowledge Granularity  establish trust values Include both trust and distrust concept

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Description Fuzzy Logic Trustworthiness  no trust for situation, category, etc. Trust properties: reflexive, non-symmetrical, conditionally transitive (explicit), dynamic Distrust 010,50,250,750,9 Trust Ignorance % of membership 0,7 0,3 Distrust threshold T(A  B) complete very highhighmediumlittlevery littlescarce none  trustworthiness

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model How it works? ➊ A (new user) requests access ➋ B searches trust information about A ➌ If A is unknown, B requests recommendations to Cs ➍ If there are trusted recommendations, B uses them (Indirect)  PRP If there are no recommendations, B uses trust rules (direct) ➎ If trust relationship is established, B recalculates trust value on A based on interactions A Recommendations ➊ ➋ ➌ ➍ B C1C1 C2C2 ➎

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Indirect Trust Formation Combining online recommendations (weigthed average)  Source trustworthiness  Lower complexity  Dempster-Shafer, normalized Dempster-Shafer, and consensus operator from Josang  Similar results  according to the intuitive human judgement Certificates are used as offline recommendations

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Mathematical Trust Evolution “ Trust comes on foot and goes by horse ” Current behaviour is measured based on: ○Current interaction  Action weight (fuzzy logic)  Security level ○Past behaviour  Positive and negative interactions  Increment factor (  i )  restriction percentage (  ) ○A priori probability If a=a +  (a + – a - )>0 else, but no attack If attack

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Mathematical Trust Evolution (II) Trust is recalculated based on: ○Current behaviour ○Previous trust value ○Strictness factor (  ) Summarizing If V a i >0 If not If I i >0 If not

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Mathematical Trust Evolution (III)

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Mathematical Trust Evolution (IV) PARAMETERS: Increment percentage: 2% Security level: m=2 Disposition Factor: 0.5 Positive action: 1 Wrong action: 0.5 (PTM) PARAMETERS: Increment percentage: 2% Security level: m=2 Disposition Factor: 0.5 Positive action: 1 Wrong action: 0.5 (PTM)

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Mathematical Trust Evolution (V) PARAMETERS: Increment percentage: 2% Security level: m =2 Disposition Factor: 0.5 Positive action: 1 Wrong action: 0.5 (PTM) 0, 0.3 (Wang) PARAMETERS: Increment percentage: 2% Security level: m =2 Disposition Factor: 0.5 Positive action: 1 Wrong action: 0.5 (PTM) 0, 0.3 (Wang)

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Probabilistic Trust Evolution Bayes’ theorem ○Posteriori probabilities Probabilities for binary events: Beta density function ○Assign belief degrees between 0 and 1 Risk model

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Pervasive Trust Management Model Probabilistic Trust Evolution (II) P(a + |H act )P(a - |H act ) a b c d e f0.500

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Component-based PTM Implementation Prototype J2ME Personal Profile OpenSSL  cryptographic API JNI wrappers XACML  Sun implementation Extended  trust, context PEP + PDP Proofs PDA  Windows Mobile 2003 Linux, Windows Available at:

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Component-based PTM Implementation Pervasive device keys, certificates, trust Cryptographic Provider Credentials Manager Communication API Applications Authentication Manager Trust Manager Recommendation Manager logs, policies Authorization Manager Context Provider Monitor

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Conclusions & Future Work Trust  basis to establish relationships in a spontaneous way Pervasive devices can interact with closed devices in a secure way, without depend on central server Simple pervasive trust management model ○to enhance the security architecture of pervasive devices ○to minimize the uncertainty and take appropriate decisions ○to allow the cooperation among closed trusted devices Mathematical and probabilistic model ○According to the intuitive human judgement ○Simple calculations

Pervasive Computing and Communication Security (PerSec 2006) March 13th, Conclusions & Future Work (II) Implementation of a generic prototype ○to demonstrate its functionality ○Security services for applications (client/server) Future work ○Integrating our model in the WCE security architecture  Trust providers ○Analyse the performance and consumption of resources

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