fix(ledger): tolerate tag-258 set duplicates in Conway witness fields (#1855)

Fixes #1853.

Signed-off-by: Chris Gianelloni <wolf31o2@blinklabs.io>

Author: wolf31o2

ledger/conway/conway.go

@@ -438,17 +438,22 @@ func (w *ConwayTransactionWitnessSet) UnmarshalCBOR(cborData []byte) error {
 	if _, err := cbor.Decode(cborData, &tmp); err != nil {
 		return err
 	}
-	// Reject duplicate members in any tag-258 witness set field.
-	// Untagged array fields are left unchecked so pre-Conway encodings remain valid.
+	// Conway (protocol versions 9-11) tolerates duplicate members in the
+	// witness-set sets that cardano-ledger decodes via Set/Map.fromList: vkey
+	// witnesses, bootstrap witnesses, native scripts, and plutus data all
+	// silently deduplicate at decode and only begin rejecting duplicates at
+	// protocol version 12 (Dijkstra, handled by DijkstraTransactionWitnessSet).
+	// Plutus script sets, by contrast, reject duplicates from version 9
+	// (cardano-ledger scriptDecoderV9 / decodeMapLikeEnforceNoDuplicates), like
+	// the tx-body sets. Only enforce the fields cardano-ledger enforces in
+	// Conway; enforcing the tolerated fields rejects valid historical blocks at
+	// decode (issue #1853). Untagged array fields are left unchecked so
+	// pre-Conway encodings remain valid.
 	type duplicateChecker interface {
 		CheckForDuplicates() error
 	}
 	for _, c := range []duplicateChecker{
-		&tmp.VkeyWitnesses,
-		&tmp.WsNativeScripts,
-		&tmp.BootstrapWitnesses,
 		&tmp.WsPlutusV1Scripts,
-		&tmp.WsPlutusData,
 		&tmp.WsPlutusV2Scripts,
 		&tmp.WsPlutusV3Scripts,
 	} {

ledger/conway/conway_test.go

@@ -306,7 +306,11 @@ func TestConwayTransactionBodyRejectsDuplicateTaggedSetFields(t *testing.T) {
 	}
 }
 
-func TestConwayWitnessSetRejectsDuplicateTaggedVkeyWitness(t *testing.T) {
+// Conway (protocol versions 9-11) tolerates duplicate vkey witnesses:
+// cardano-ledger decodes them via Set.fromList and only begins rejecting
+// duplicates at protocol version 12 (Dijkstra). Rejecting at decode in Conway
+// wrongly rejects valid historical blocks (issue #1853).
+func TestConwayWitnessSetToleratesDuplicateTaggedVkeyWitness(t *testing.T) {
 	dupCbor := []byte{
 		0xa1,             // map(1)
 		0x00,             // key: 0  (VkeyWitnesses field)
@@ -316,11 +320,100 @@ func TestConwayWitnessSetRejectsDuplicateTaggedVkeyWitness(t *testing.T) {
 		0x82, 0x41, 0x01, 0x41, 0x02, // duplicate
 	}
 
+	var ws ConwayTransactionWitnessSet
+	err := ws.UnmarshalCBOR(dupCbor)
+	assert.NoError(t, err,
+		"Conway must tolerate duplicate vkey witnesses (dedup at decode, matching cardano-ledger pv 9-11)")
+}
+
+func TestConwayWitnessSetToleratesDuplicateTaggedWitnessSetFields(t *testing.T) {
+	tests := []struct {
+		name   string
+		field  byte
+		member []byte
+	}{
+		{
+			name:  "bootstrap witnesses",
+			field: 0x02,
+			member: []byte{
+				0x84,                   // BootstrapWitness
+				0x41, 0x01, 0x41, 0x02, // public key, signature
+				0x41, 0x03, 0x41, 0x04, // chain code, attributes
+			},
+		},
+		{
+			name:   "native scripts",
+			field:  0x01,
+			member: []byte{0x82, 0x00, 0x41, 0x01}, // pubkey script
+		},
+		{
+			name:   "plutus data",
+			field:  0x04,
+			member: []byte{0x00}, // integer datum
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var ws ConwayTransactionWitnessSet
+			err := ws.UnmarshalCBOR(
+				duplicateTaggedWitnessSetFieldCbor(tt.field, tt.member),
+			)
+			assert.NoError(t, err)
+		})
+	}
+}
+
+// Plutus script sets reject duplicates from protocol version 9 (cardano-ledger
+// scriptDecoderV9), so Conway must still reject them at decode.
+func TestConwayWitnessSetRejectsDuplicateTaggedPlutusV1Script(t *testing.T) {
+	dupCbor := []byte{
+		0xa1,             // map(1)
+		0x03,             // key: 3  (WsPlutusV1Scripts field)
+		0xd9, 0x01, 0x02, // tag(258) - CBOR set
+		0x82,       // array(2)
+		0x41, 0x01, // PlutusV1Script [0x01]
+		0x41, 0x01, // duplicate
+	}
+
 	var ws ConwayTransactionWitnessSet
 	err := ws.UnmarshalCBOR(dupCbor)
 	assert.ErrorContains(t, err, "duplicate member in set")
 }
 
+func TestConwayWitnessSetRejectsDuplicateTaggedPlutusV2AndV3Scripts(t *testing.T) {
+	tests := []struct {
+		name  string
+		field byte
+	}{
+		{name: "Plutus V2", field: 0x06},
+		{name: "Plutus V3", field: 0x07},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var ws ConwayTransactionWitnessSet
+			err := ws.UnmarshalCBOR(
+				duplicateTaggedWitnessSetFieldCbor(
+					tt.field,
+					[]byte{0x41, 0x01},
+				),
+			)
+			assert.ErrorContains(t, err, "duplicate member in set")
+		})
+	}
+}
+
+func duplicateTaggedWitnessSetFieldCbor(field byte, member []byte) []byte {
+	ret := []byte{
+		0xa1,             // map(1)
+		field,            // witness set field key
+		0xd9, 0x01, 0x02, // tag(258) - CBOR set
+		0x82, // array(2)
+	}
+	ret = append(ret, member...)
+	ret = append(ret, member...)
+	return ret
+}
+
 func testConwayShelleyInput() shelley.ShelleyTransactionInput {
 	var txId common.Blake2b256
 	txId[0] = 1