Computer Laboratory

Technical reports

On two formal analyses of the Yahalom protocol

Lawrence C. Paulson

July 1997, 16 pages


The Yahalom protocol is one of those analyzed by Burrows et al. in the BAN paper. Based upon their analysis, they have proposed modifications to make the protocol easier to understand and analyze. Both versions of Yahalom have now been proved, using Isabelle/HOL, to satisfy strong security goals. The mathematical reasoning behind these machine proofs is presented informally.

The new proofs do not rely on a belief logic; they use an entirely different formal model, the inductive method. They confirm the BAN analysis and the advantages of the proposed modifications. The new proof methods detect more flaws than BAN and analyze protocols in finer detail, while remaining broadly consistent with the BAN principles. In particular, the proofs confirm the explicitness principle of Abadi and Needham.

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BibTeX record

  author =	 {Paulson, Lawrence C.},
  title = 	 {{On two formal analyses of the Yahalom protocol}},
  year = 	 1997,
  month = 	 jul,
  url = 	 {},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-432}