pulsar: prove luxfi/dkg CSCP bridge w1 == ideal oracle == HighBits(A·ȳ) (step 4 fidelity)

ref/go/pkg/pulsar/talus_cscp_dkg_test.go

@@ -0,0 +1,60 @@
+// Copyright (C) 2025-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package pulsar
+
+// talus_cscp_dkg_test.go — Phase-3b CSCP-lift fidelity proof (step 4).
+//
+// Proves the deduplication is byte-faithful: the production CarryCompare now
+// runs on the SHARED, malicious-secure luxfi/dkg cscp.SecureHighBitsVec (via the
+// cscpSecureHighBitsVecDKG bridge), and its w1 is identical to BOTH
+//
+//  1. the in-house ideal functionality cefIdealSecureHighBits — kept in pulsar
+//     as the test oracle per the Phase-3b handoff, and
+//  2. the ground truth HighBits(A·ȳ) computed in the clear,
+//
+// for ML-DSA-65 (K=6) and ML-DSA-87 (K=8, exercising the K-override profile
+// shim). This is a direct, per-coefficient proof of the lift's correctness that
+// complements the end-to-end stock-FIPS-204 round-trip
+// (TestTalus_MPC_EndToEnd_StockVerify / _Mode87): the round-trip proves the
+// signature verifies; this proves the secure-comparison output itself is exact.
+
+import (
+	"crypto/rand"
+	"testing"
+)
+
+// TestCSCP_DKGBridge_MatchesIdealOracle proves the luxfi/dkg malicious-secure
+// CSCP bridge realises the same ideal HighBits functionality as the retained
+// in-house oracle, and matches the cleartext ground truth — for both in-scope
+// parameter sets.
+func TestCSCP_DKGBridge_MatchesIdealOracle(t *testing.T) {
+	for _, mode := range []Mode{ModeP65, ModeP87} {
+		const n, threshold = 5, 3
+		var nonceID [32]byte
+		nonceID[0] = 0xD0
+		nonceID[1] = byte(mode)
+		_, _, bus, evalPoints, wGround := cscpCommitteeBus(t, mode, n, threshold, nonceID)
+
+		// Production path: the shared luxfi/dkg malicious-secure CSCP.
+		got, err := cscpSecureHighBitsVecDKG(mode, bus, evalPoints, threshold, rand.Reader)
+		if err != nil {
+			t.Fatalf("%s dkg CSCP bridge: %v", mode, err)
+		}
+
+		// (1) equals the in-house ideal functionality (retained test oracle).
+		want, err := cefIdealSecureHighBits(bus, mode)
+		if err != nil {
+			t.Fatalf("%s ideal oracle: %v", mode, err)
+		}
+		if !polyVecEqual(got, want) {
+			t.Fatalf("%s dkg CSCP bridge w1 ≠ ideal F_HighBits", mode)
+		}
+
+		// (2) equals the cleartext ground truth HighBits(A·ȳ).
+		gamma2, _, _, _ := bccParams(mode)
+		if !polyVecEqual(got, highBitsVec(wGround, gamma2)) {
+			t.Fatalf("%s dkg CSCP bridge w1 ≠ HighBits(A·ȳ)", mode)
+		}
+	}
+}