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htlcswitch/hop: require total_amount_msat for blinded final hops #10597

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htlcswitch/hop: require total_amount_msat for blinded final hops #10597

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htlcswitch/hop: require total_amount_msat for blinded final hops
erickcestari Feb 17, 2026
774960d
docs: add release-notes
erickcestari Feb 18, 2026
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6 changes: 6 additions & 0 deletions docs/release-notes/release-notes-0.21.0.md
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Original file line number Diff line number Diff line change
Expand Up @@ -75,6 +75,12 @@
transitions during startup, avoiding lost unlocks during slow database
initialization.

* [Required `total_amount_msat` for blinded final
hops](https://github.com/lightningnetwork/lnd/pull/10597). Per BOLT 4, when
`encrypted_recipient_data` is present on a final node, `total_amount_msat`
must be included. Validation is now performed explicitly at payload parsing
time.

# New Features

- Basic Support for [onion messaging forwarding](https://github.com/lightningnetwork/lnd/pull/9868)
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10 changes: 10 additions & 0 deletions htlcswitch/hop/payload.go
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Expand Up @@ -275,6 +275,7 @@ func ValidateParsedPayloadTypes(parsedTypes tlv.TypeMap,
_, hasAMP := parsedTypes[record.AMPOnionType]
_, hasEncryptedData := parsedTypes[record.EncryptedDataOnionType]
_, hasBlinding := parsedTypes[record.BlindingPointOnionType]
_, hasTotalAmtMsatBlinded := parsedTypes[record.TotalAmtMsatBlindedType]

// All cleartext hops (including final hop) and the final hop in a
// blinded path require the forwading amount and expiry TLVs to be set.
Expand Down Expand Up @@ -311,6 +312,15 @@ func ValidateParsedPayloadTypes(parsedTypes tlv.TypeMap,
FinalHop: isFinalHop,
}

// If encrypted data is present and is final hop, we require that
// total_amount_msat is set.
case isFinalHop && hasEncryptedData && !hasTotalAmtMsatBlinded:
return ErrInvalidPayload{
Type: record.TotalAmtMsatBlindedType,
Violation: OmittedViolation,
FinalHop: isFinalHop,
}

// Hops that need forwarding info must include an amount to forward.
case needFwdInfo && !hasAmt:
return ErrInvalidPayload{
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25 changes: 25 additions & 0 deletions htlcswitch/hop/payload_test.go
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Expand Up @@ -377,6 +377,8 @@ var decodePayloadTests = []decodePayloadTest{
0x04, 0x00,
// encrypted data
0x0a, 0x03, 0x03, 0x02, 0x01,
// total_amount
0x12, 0x00,
},
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@ziggie1984 ziggie1984 Feb 19, 2026

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Nit: the zero-length value here (0x12, 0x00) — type 18, length 0 — decodes as 0 for a tuint64, but is enough to mark the field as present in the parsed type map, which is all this layer checks. Worth a short comment to make that intent clear.

shouldHaveEncData: true,
},
Expand All @@ -389,6 +391,8 @@ var decodePayloadTests = []decodePayloadTest{
0x04, 0x00,
// encrypted data
0x0a, 0x03, 0x03, 0x02, 0x01,
// total_amount
0x12, 0x00,
},
shouldHaveEncData: true,
expErr: hop.ErrInvalidPayload{
Expand All @@ -397,6 +401,25 @@ var decodePayloadTests = []decodePayloadTest{
FinalHop: true,
},
},
{
name: "final blinded missing total_amount",
isFinalHop: true,
updateAddBlinded: true,
payload: []byte{
// amount
0x02, 0x00,
// cltv
0x04, 0x00,
// encrypted data
0x0a, 0x03, 0x03, 0x02, 0x01,
},
shouldHaveEncData: true,
expErr: hop.ErrInvalidPayload{
Type: record.TotalAmtMsatBlindedType,
Violation: hop.OmittedViolation,
FinalHop: true,
},
},
{
name: "final blinded missing cltv",
isFinalHop: true,
Expand All @@ -406,6 +429,8 @@ var decodePayloadTests = []decodePayloadTest{
0x02, 0x00,
// encrypted data
0x0a, 0x03, 0x03, 0x02, 0x01,
// total_amount
0x12, 0x00,
},
shouldHaveEncData: true,
expErr: hop.ErrInvalidPayload{
Expand Down
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