Authenticated Traversal Sectrace Protocol Contessa

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Authenticated TraversalSectrace ProtocolContessa

• Carl A. Gunter, Alwyn Goodloe, Michael McDougall
• April 1, 2003

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What is the Problem?

• We need to connect security gateways to each
  other
• Amortize costs
• AST is insufficient because it resets on every
  connection
• IPSec gives us the tools, but there is no
  automated setup protocol

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Why is it Hard?
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Options
Security Gateways
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Trust Relations
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Options
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Long SAs
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Options
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Short SAs
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Options
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Conflicting SAs
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Design

• Philosophy
• Assumes gateways are willing to forward traffic
  if
• it is authenticated by an a trusted upstream
  gateway or
• it is intended to establish a trusted channel
• Leverages IPSec security measures
• Initiator traffic is treated differently than
  response traffic
• Request to open session must be authenticated
• Session traffic assumed ok

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Theory

• There is a canonical choice of shortest SA each
  node chooses the nearest trusted source that is
  consistent with choices earlier on the path.

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Theory

• Theorem if an SA path exists, then this
  canonical choice provides a path.
• Proof by induction on the nodes in the path. Let
• fSA path on n1 nodes
• fscanonical path on n nodes
• f restricted to n nodes is a valid path
• Induction shows that the SAs in fs are shorter
  than the corresponding paths in f

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Algorithm
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Algorithm
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Available Endpoints
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Algorithm
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Available Endpoints
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C
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Trust relationship
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Algorithm
C
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Available Endpoints
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C
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Algorithm
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Available Endpoints
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Algorithm
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Available Endpoints
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Algorithm
Available Endpoints
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Sectrace protocol

• Resembles traceroute protocol
• Client repeatedly sends messages towards the
  server
• Gateways respond with information about their
  policy
• Client chooses two endpoints for IPSec SA

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Sectrace Protocol
Access Point
Mail Server
Client
Firewall
Firewall
Widget Com
Generic Ltd
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Sectrace Protocol
Access Point
Mail Server
Client
Firewall
Firewall
Widget Com
Generic Ltd
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Sectrace Protocol

• Messages
• RReq Route Request
• I want a connection to the server
• RRep Route Reply
• Here is my certificate and who I trust
• SAReq SA Request
• Please set up a tunnel with
• SARep SA Reply
• Tunnel setup has succeeded/failed

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Sectrace Protocol
Access Point
Mail Server
Client
Firewall
Firewall
Widget Com
Generic Ltd
23
Sectrace Protocol
Access Point
Mail Server
Client
Firewall
Firewall
Widget Com
Generic Ltd
24
Sectrace Protocol
Access Point
Mail Server
Client
Firewall
Firewall
Widget Com
Generic Ltd
25
Sectrace Protocol
Access Point
Mail Server
Client
Firewall
Firewall
Widget Com
Generic Ltd
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Sectrace Protocol

• Characteristics
• Gateways and Servers are stateless with respect
  to the sectrace protocol
• Though sectrace triggers protocols that establish
  state
• All SAReq messages arrive through a secure tunnel
• RReq messages are only forwarded if they are
  authenticated

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Implementation

• Goals
• Proof of concept
• Packet formats, timers
• Verify protocol document
• Bottom up
• Concrete framework to explore any issues that
  arise in formal verification
• Idea of the interface with routing and IPSec
• What is the minimal routing and IPSec
  functionality required by the protocol

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Implementation

• Simulate routing and IPSec
• As simple as possible while supporting sectrace
• Actual network packets
• Verify a reasonable byte-level representation of
  packets
• Real world network behavior
• Distributed across Processes or Machines
• Implemented in Java

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Related Work

• IETF working groups
• IP Security Policy (ipsp)
• Middlebox Communication (midcom)
• Security Policy Protocol - DARPA/BBN
• Expired IETF draft
• No known formal analysis or implementation
• Very complex 160 pages
• RSVP Protocol
• Opportunistic Encryption

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Lessons Future Work

• Lessons learned
• Protocol works
• Interface with routing and IPSec is the trickiest
  issue
• What do SAs cover?
• What functionality does sectrace demand?
• Future
• Aggregation/out of band SA
• Multiple clients and server
• Integration with routing and IPSec code
• Hardening the protocol with more DoS protection