Enforces low-S canonical signatures when the n field is present in a BOLT11 invoice

docs/release-notes/release-notes-0.21.0.md

@@ -61,6 +61,9 @@
 # Technical and Architectural Updates
 ## BOLT Spec Updates
 
+LND now [enforces](https://github.com/lightning/bolts/pull/1284) low-S canonical
+signatures when `n` field is present in a BOLT11 invoice.
+
 ## Testing
 
 ## Database
@@ -78,3 +81,4 @@
 * Boris Nagaev
 * Elle Mouton
 * Nishant Bansal
+* Pins

zpay32/decode.go

@@ -186,6 +186,10 @@
 			return nil, fmt.Errorf("unable to deserialize "+
 				"signature: %v", err)
 		}
+		// Ensure the signature is in canonical low-S form.
+		if err = ecdsa.VerifyLowS(sig.ToSignatureBytes()); err != nil {		
+			return nil, err
+		}
 		if !signature.Verify(hash, decodedInvoice.Destination) {
 			return nil, fmt.Errorf("invalid invoice signature")
 		}

zpay32/invoice_test.go

@@ -22,6 +22,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+//nolint:ll
 var (
 	testMillisat24BTC    = lnwire.MilliSatoshi(2400000000000)
 	testMillisat2500uBTC = lnwire.MilliSatoshi(250000000)
@@ -61,6 +62,9 @@ var (
 	testPrivKeyBytes, _     = hex.DecodeString("e126f68f7eafcc8b74f54d269fe206be715000f94dac067d1c04a8ca3b2db734")
 	testPrivKey, testPubKey = btcec.PrivKeyFromBytes(testPrivKeyBytes)
 
+	testHighSPubKeyBytes, _ = hex.DecodeString("02d0139ce7427d6dfffd26a326c18be754ef1e64672b42694ba5b23ef6e6e7803d")
+	testHighSPubKey, _      = btcec.ParsePubKey(testHighSPubKeyBytes)
+
 	testDescriptionHashSlice = chainhash.HashB([]byte("One piece of chocolate cake, one icecream cone, one pickle, one slice of swiss cheese, one slice of salami, one lollypop, one piece of cherry pie, one sausage, one cupcake, and one slice of watermelon"))
 
 	testExpiry0  = time.Duration(0) * time.Second
@@ -898,6 +902,35 @@ func TestDecodeEncode(t *testing.T) {
 				WithErrorOnUnknownFeatureBit(),
 			},
 		},
+		{
+			// Invoice with high-S signature and Public-key
+			// recovery.
+			encodedInvoice: "lnbc1pvjluezsp5zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zygspp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdpl2pkx2ctnv5sxxmmwwd5kgetjypeh2ursdae8g6twvus8g6rfwvs8qun0dfjkxaq9qrsgq357wnc5r2ueh7ck6q93dj32dlqnls087fxdwk8qakdyafkq3yap2r09nt4ndd0unm3z9u5t48y6ucv4r5sg7lk98c77ctvjczkspk5qprc90gx",
+			valid:          true,
+			skipEncoding:   true,
+			decodedInvoice: func() *Invoice {
+				return &Invoice{
+					Net:         &chaincfg.MainNetParams,
+					Timestamp:   time.Unix(1496314658, 0),
+					PaymentHash: &testPaymentHash,
+					PaymentAddr: fn.Some(specPaymentAddr),
+					Description: &testPleaseConsider,
+					Destination: testHighSPubKey,
+					Features: lnwire.NewFeatureVector(
+						lnwire.NewRawFeatureVector(
+							8, 14,
+						),
+						lnwire.Features,
+					),
+				}
+			},
+		},
+		{
+			// Invoice with high-S signature and 'n' tagged field
+			// for destination pubkey.
+			encodedInvoice: "lnbc25m1p70xwfzpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdpl2pkx2ctnv5sxxmmwwd5kgetjypeh2ursdae8g6twvus8g6rfwvs8qun0dfjkxaqnp4q0n326hr8v9zprg8gsvezcch06gfaqqhde2aj730yg0durunfhv66sp5zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zygs9qrsgqsp5zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zyg3zygsp5cfzp9ugllvk03rltd6hvndxj26ux6gcxc5azyxk060rj9tzghct5zvjlps76gx8wpq5yuu79688k8gnm2c0al6v608s96l0xzrrlqqwnzxmu",
+			valid:          false,
+		},
 	}
 
 	for i, test := range tests {