tendermint/ivy-proofs/accountable_safety_2.ivy

#lang ivy1.7

include tendermint
include abstract_tendermint

# Here we prove the second accountability property: no well-behaved node is
# every observed to violate the accountability properties.

# The proof is done in two steps: first we prove the the abstract specification
# satisfies the property, and then we show by refinement that this property
# also holds in the concrete specification.

# To see what is checked in the refinement proof, use `ivy_show isolate=accountable_safety_2 accountable_safety_2.ivy`
# To see what is checked in the abstract correctness proof, use `ivy_show isolate=abstract_accountable_safety_2 accountable_safety_2.ivy`
# To check the whole proof, use `ivy_check accountable_safety_2.ivy`.

# Proof that the property holds in the abstract specification
# ============================================================

isolate abstract_accountable_safety_2 = {

    instantiate abstract_tendermint

# the main property:
    invariant [wb_never_punished] well_behaved(N) -> ~(observed_equivocation(N) | observed_unlawful_prevote(N))

# the main invariant for proving wb_not_punished:
    invariant well_behaved(N) & precommitted(N,R,V) & ~locked(N,R,V) & V ~= value.nil -> exists R2,V2 . V2 ~= value.nil & R < R2 & precommitted(N,R2,V2) & locked(N,R2,V2)

    invariant (exists N . well_behaved(N) & precommitted(N,R,V) & V ~= value.nil) -> exists Q . nset.is_quorum(Q) & forall N . nset.member(N,Q) -> observed_prevoted(N,R,V)

    invariant well_behaved(N) -> (observed_prevoted(N,R,V) <-> prevoted(N,R,V))
    invariant well_behaved(N) -> (observed_precommitted(N,R,V) <-> precommitted(N,R,V))

# nodes stop prevoting or precommitting in lower rounds when doing so in a higher round:
    invariant well_behaved(N) & prevoted(N,R2,V2) & R1 < R2 -> left_round(N,R1)
    invariant well_behaved(N) & locked(N,R2,V2) & R1 < R2 -> left_round(N,R1)

    invariant [precommit_unique_per_round] well_behaved(N) & precommitted(N,R,V1) & precommitted(N,R,V2) -> V1 = V2

} with nset, round, abstract_accountable_safety_2.defs.observed_equivocation_def, abstract_accountable_safety_2.defs.observed_unlawful_prevote_def

# Proof that the property holds in the concrete specification
# ===========================================================

isolate accountable_safety_2 = {

    instantiate tendermint(abstract_accountable_safety_2)

    invariant well_behaved(N) -> ~(abstract_accountable_safety_2.observed_equivocation(N) | abstract_accountable_safety_2.observed_unlawful_prevote(N))

} with round, value, shim, abstract_accountable_safety_2, abstract_accountable_safety_2.defs.observed_equivocation_def, abstract_accountable_safety_2.defs.observed_unlawful_prevote_def