Protocol Independence through Disjoint Encryption

  • Authors:
  • Joshua D. Guttman;F. Javier Thayer

  • Affiliations:
  • -;-

  • Venue:
  • CSFW '00 Proceedings of the 13th IEEE workshop on Computer Security Foundations
  • Year:
  • 2000

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Abstract

One protocol (called the primary protocol) is independent of other protocols (jointly called the secondary protocol) if the question whether the primary protocol achieves a security goal never depends on whether the secondary protocol is in use.In this paper, we use multiprotocol strand Spaces {ThayerHerzogGuttman99a}, cf. {ThayerHerzogGuttman99}) to prove that two cryptographic protocols are independent if they use encryption in non-overlapping ways. This theorem (Proposition {prop: prot: independence}) applies even if the protocols share public key certificates and secret key 驴tickets.驴We use the method of {GuttmanThayer00a, GuttmanThayer00} to study penetrator paths, namely sequences of penetrator actions connecting regular nodes (message transmissions or receptions) in the two protocols. Of special interest are inbound linking paths, which lead from a message transmission in the secondary protocol to a message reception in the primary protocol. We show how to modify any bundle to remove all inbound linking paths, if encryption does not overlap in the two protocols. The resulting bundle no longer depends on any activity of the secondary protocol.We illustrate this method using the Neuman-Stubblebine protocol as an example {NeumanStubblebine93, ThayerHerzogGuttman99a}.