Fs Abort Sign Loop cache invariant
FiatShamirWithAbort.fsAbortSignLoop_cache_invariant
Plain-language statement
When the simulated signing loop produces some (w, z), the random-oracle cache contains a challenge c at (msg, w) satisfying ids.verify pk w c z = true. This is proved by induction on the loop counter: each abort iteration preserves the invariant (the cache only grows), and a successful iteration writes exactly the challenge used in verification.
Exact Lean statement
lemma fsAbortSignLoop_cache_invariant
(ro : QueryImpl (M × Commit →ₒ Chal)
(StateT ((M × Commit →ₒ Chal).QueryCache) ProbComp))
(hro : ro = randomOracle)
(hc : ids.Complete) {pk : Stmt} {sk : Wit} (hrel : rel pk sk = true)
(msg : M) (n : ℕ) (s₀ : (M × Commit →ₒ Chal).QueryCache)
(w : Commit) (z : Resp) (s : (M × Commit →ₒ Chal).QueryCache)
(hsup : (some (w, z), s) ∈ support
((simulateQ (unifFwdImpl (M × Commit →ₒ Chal) + ro)
(fsAbortSignLoop ids M pk sk msg n)).run s₀)) :
∃ c : Chal, s (msg, w) = some c ∧ ids.verify pk w c z = trueFormal artifact
Lean source
lemma fsAbortSignLoop_cache_invariant (ro : QueryImpl (M × Commit →ₒ Chal) (StateT ((M × Commit →ₒ Chal).QueryCache) ProbComp)) (hro : ro = randomOracle) (hc : ids.Complete) {pk : Stmt} {sk : Wit} (hrel : rel pk sk = true) (msg : M) (n : ℕ) (s₀ : (M × Commit →ₒ Chal).QueryCache) (w : Commit) (z : Resp) (s : (M × Commit →ₒ Chal).QueryCache) (hsup : (some (w, z), s) ∈ support ((simulateQ (unifFwdImpl (M × Commit →ₒ Chal) + ro) (fsAbortSignLoop ids M pk sk msg n)).run s₀)) : ∃ c : Chal, s (msg, w) = some c ∧ ids.verify pk w c z = true := by subst hro set impl := unifFwdImpl (M × Commit →ₒ Chal) + (randomOracle : QueryImpl (M × Commit →ₒ Chal) _) have hSimQuery : ∀ (q : M × Commit), simulateQ impl (HasQuery.query q) = (randomOracle : QueryImpl (M × Commit →ₒ Chal) _) q := roSim.simulateQ_HasQuery_query _ induction n generalizing s₀ with | zero => simp [fsAbortSignLoop, simulateQ_pure, StateT.run_pure, support_pure] at hsup | succ n ih => simp only [fsAbortSignLoop, simulateQ_bind] at hsup rw [StateT.run_bind] at hsup obtain ⟨⟨⟨w_a, oz⟩, s₁⟩, h_attempt, h_rest⟩ := (mem_support_bind_iff _ _ _).mp hsup cases oz with | none => exact ih s₁ (by simpa using h_rest) | some z_a => obtain ⟨⟨rfl, rfl⟩, rfl⟩ : (some (w, z), s) = (some (w_a, z_a), s₁) := by simpa using h_rest simp only [fsAbortSignAttempt, simulateQ_bind, hSimQuery, simulateQ_pure, StateT.run_bind, mem_support_bind_iff, StateT.run_pure, support_pure, Set.mem_singleton_iff, Prod.mk.injEq] at h_attempt obtain ⟨⟨⟨w_cm, st⟩, s_cm⟩, h_commit, ⟨c_q, s_ro⟩, h_query, ⟨oz_r, s_resp⟩, h_respond, ⟨rfl, rfl⟩, rfl⟩ := h_attempt change _ ∈ support ((simulateQ impl (liftM (ids.commit pk sk))).run s₀) at h_commit rw [roSim.run_liftM, support_map] at h_commit obtain ⟨⟨w_c, st_c⟩, h_cm_mem, h_cm_eq⟩ := h_commit simp only [Prod.mk.injEq] at h_cm_eq obtain ⟨⟨rfl, rfl⟩, rfl⟩ := h_cm_eq change _ ∈ support ((simulateQ impl (liftM (ids.respond pk sk st_c c_q))).run s_ro) at h_respond rw [roSim.run_liftM, support_map] at h_respond obtain ⟨_, h_rsp_mem, rfl, rfl⟩ := h_respond refine ⟨c_q, ?_, ?_⟩ · simp only [randomOracle, QueryImpl.withCaching_apply, StateT.run_bind, StateT.run_get, pure_bind] at h_query cases hs : s₀ (msg, w_c) with | some c_cached => simp only [hs, StateT.run_pure, support_pure, Set.mem_singleton_iff, Prod.mk.injEq] at h_query rw [h_query.2, hs, h_query.1] | none => simp only [hs, StateT.run_bind, mem_support_bind_iff, StateT.run_modifyGet, support_pure, Set.mem_singleton_iff, Prod.mk.injEq] at h_query obtain ⟨x, -, rfl, rfl⟩ := h_query exact QueryCache.cacheQuery_self _ (msg, w_c) x.1 · apply ids.verify_of_complete hc hrel rw [IdenSchemeWithAbort.honestExecution, support_bind] refine Set.mem_iUnion₂.mpr ⟨(w_c, st_c), h_cm_mem, ?_⟩ rw [support_bind] refine Set.mem_iUnion₂.mpr ⟨c_q, mem_support_uniformSample _, ?_⟩ simp only [support_bind, Set.mem_iUnion₂, support_pure, Set.mem_singleton_iff] exact ⟨some z, h_rsp_mem, by simp [Option.map]⟩- Project
- VCVio
- License
- Apache-2.0
- Commit
- 2ceb2d825ee3
- Source
- VCVio/CryptoFoundations/FiatShamir/WithAbort.lean:136-200
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