SRI International Computer Science Laboratory
Formal Verification of an Oral Messages Algorithm for Interactive
Consistency
John Rushby
Technical Report CSL-92-01, July 1992
Also available as NASA Contractor Report 189704, October 1992
Abstract
We describe the formal specification and verification of an algorithm
for Interactive Consistency based on the Oral Messages algorithm for
Byzantine Agreement. We compare our treatment with that of Bevier and
Young, who presented a formal specification and verification for a
very similar algorithm. Unlike Bevier and Young, who observed that
``the invariant maintained in the recursive subcases of the algorithm
is significantly more complicated than is suggested by the published
proof'' and who found its formal verification ``a fairly difficult
exercise in mechanical theorem proving,'' our treatment is very close
to the previously published analysis of the algorithm, and our formal
specification and verification are straightforward.
This example illustrates how delicate choices in the formulation of a
problem can have significant impact on the readability of its formal
specification and on the tractability of its formal verification.
dvi
or
postscript
New: PVS specification files for a treatment based on Appendix B are
now available
PVS specification files
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