Mobile Trust Negotiation Authentication and Authorization in Dynamic Mobile Networks Tim van der Horst, Tore Sundelin, Kent Seamons, and Charles Knutson Internet Security Research Lab Brigham Young University http://isrl.cs.byu.edu Say who I am joint work with colleaues in the ISRL base on what has happened previously Eighth IFIP TC-6 TC-11 Conference on Communications and Multimedia Security 15-18 September 2004

Outline Motivation Trust Negotiation Surrogate Trust Negotiation How to adapt trust negotiation for mobile devices Conclusions Future Work

Motivation Mobile devices often operate outside their trusted domain Have a greater need to determine whether a stranger can be trusted Identity is often irrelevant to the access control decision Access control attributes: citizenship, clearance, job classification, group memberships, licenses, role within an organization, etc.

Trust Negotiation Provides authentication based on attributes rather than identity Establishes trust through the gradual and iterative exchange of credentials. Exchange is governed by access control policies Ideal for open systems Participants are not in the same security domain The credential is not released until the policy protecting it is satisfied.

Trust Negotiation Example Fire Chief Fred the Fire Chief 1 City of “Far Away” Server Info 2 Step 1: Fred requests information from Server Step 2: Server returns access control policy for the info 2 Step 3: Fred discloses his access control policy 1 Be more direct about satisfaction of the policy Participants don’t know about Unique thing of policies, don’t know policies in advance Use Fred in the Network Messages – Check  Do a TN example that has to do with the mobile environment Disaster Scenario Fire or Paramedic They have a PDA and need information Fire Chief. Needs a schematic of the building that is on fire, or other information about building such as hazardous materials inside. Fire Chief contacts server (other fire chiefs laptop in the command vehicle or the city server) and requests the information Step 4: Server discloses his Server credential Step 5: Fred discloses his Fire Chief credential Fire Chief Step 6: Server grants access to the information Info

Security for Sensitive Credentials Trust Agent Intelligent, autonomous software module Performs trust negotiation on behalf of the user Protects and manages credentials, policies, and private keys during the negotiation Local – resides on the user’s device Remote – resides on another device Secure Repository Architechure Components of TN architechure Think about title

Mobile Environment Hazards to mobile devices Theft Accidental destruction Changes in the communication topology Limited computational resources where does this go? new hazards to what? work on transition

Secure Repository Stores sensitive information when not in use by the trust agent Types of repositories Local Remote

Local Repository Travels with the user Types Within device PKCS#12 Java KeyStore An attached secure module Sony Memory Stick Smart Card

Local Repository Advantages Disadvantages Always available Fast access Replication and synchronization Loss of device = Loss of repository

Remote Repository Does not travel with the user Types* Virtual smart card NSD Security’s Practical PKI Virtual soft token Securely Available Credentials (SACRED) Forgot to mention SACRED *Sandu et al., PKI Research Workshop 2002

Remote Repository Advantages Disadvantages Can be available even if user doesn’t have his device Loss of device ≠ Loss of repository Disadvantages Availability and accessibility Communication overhead Attractive target for attack

Hybrid Repository Local and remote repositories both have drawbacks Combination of these could lead to the elimination of these disadvantages Ability to be: Fully remote Fully local (full copy still exists remotely) Mix of local and remote Work in progress Paper submitted to NDSS’05 Collaborated with NCSA to create implementation of SACRED http://sacred.sourceforge.net

Typical Trust Negotiation Fire Chief Fred City of “Far Away” After explanation, we are now going to view one paradigm of tn in a mobile environment Trust Agent Trust Agent Repository Repository

Surrogate Trust Negotiation Agent Repository Fire Chief Fred City of “Far Away” Surrogate Trust Agents

Topologies Bilateral Unilateral Proxy ? Intermittent Internet Internet Before we view the Network Messages in detail, lets look at the commmunication topologies of the mobile environment Mention how one device will be used as a proxy Internet ? Intermittent

Surrogate Trust Negotiation Remote trust agent with remote repository Mobile Devices Pre-established relationship Compromised Device Trust agent, the credentials, and keys reside on a physically secure server Terminate relationship with device from the server Terms – use pictures Primary device Client Server Surrogate Trust Agents Trust Negotiation

Networking Messages Message phases Assume unilateral topology Transaction request Authorization Trust Negotiation Setup Trust Negotiation Trust Negotiation Response Transaction Assume unilateral topology Going to show unilateral topology, bilateral is a natural extension of this format as well as possible to be able to be done in this format.

Networking Messages Phase: Transaction Request Transaction Request Far Away’s Agent City of “Far Away” Server Fred’s Fire Chief Fred Transaction Request Focus on why, leave messages from paper

Networking Messages Phase: Authorization: Trust Negotiation Setup Far Away’s Agent City of “Far Away” Server Fred’s Fire Chief Fred Trust Negotiation Request Infrastructure Negotiation Trust_Negotiation_TicketC,CA Trust_Negotiation_TicketS,SA Our implementation uses a Shared symmetric key Infrastructure Negotiation explanation Trust_Negotiation_TicketC,CA

City of “Far Away” Server Network Messages Phase: Authorization: Trust Negotiation Far Away’s Agent City of “Far Away” Server Fred’s Fire Chief Fred Info City of “Far Away” Server Fred the Fire Chief Session_Parameters

Network Messages Phase: Authorization: Trust Negotiation Response Far Away’s Agent City of “Far Away” Server Fred’s Fire Chief Fred Transaction_TicketCA,C Transaction_TicketSA,S Transaction_TicketCA,C

Session Initialization Network Messages Phase: Transaction Far Away’s Agent City of “Far Away” Server Fred’s Fire Chief Fred Session Initialization Transaction

Security Provisions Goals Integrity Authenticity Confidentiality Termination doesn’t affect other relationships with other devices can re-initialize the relationship if device is recovered.

Security Provisions Cryptographic Tickets An encrypted container Use pre-established relationship between device and trust agent to encrypt Trust_Negotiation_Ticket Instructions from the device to the trust agent Transaction_Ticket Results of the negotiation from the trust agent to the device

Security Provisions Secure End-to-End Protocol After trust is established session keys are created Write key MAC key Each side uses a unique key to encrypt messages and a different unique key to encrypt a message verification. Any protocol IPSec’s Encapsulating Security Payload (ESP) Specific examples

Implementation Primary Devices Trust Agents Two WiFi-enabled iPAQs STN Mobile Module TCP sockets over 802.11b Trust Agents Two Pentium 4 desktops TrustBuilder SOAP RPC

Conclusions First look at trust negotiation in the mobile environment Examined the responsibilities of repositories and trust agents in the mobile environment Presented surrogate trust negotiation Makes trust negotiation accessible to mobile devices of limited resources Shifts the resource-intensive task of authentication to a remote agent Added privacy and security to mobile devices First look at TN in the Mobile environment Added privacy and security to the mobile devices Reinforce the contributions

Future Work STN only works in bilateral and unilateral topologies Intermittent topology System in which the user can choose how and where the trust agent and repository will exist Hybrid repository Trust agent capable of mixed degrees of locality and remoteness

Further Information BYU Internet Security Research Lab http://isrl.cs.byu.edu Master’s Thesis by Tore Sundelin