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BOLT 4: Merge final_expiry_too_soon into incorrect_or_unknown_payment #608

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Aug 19, 2019
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BOLT 4: Merge final_expiry_too_soon into incorrect_or_unknown_payment #608

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42 changes: 26 additions & 16 deletions 04-onion-routing.md
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Original file line number Diff line number Diff line change
Expand Up @@ -825,21 +825,31 @@ handling by the processing node.
1. type: PERM|15 (`incorrect_or_unknown_payment_details`)
2. data:
* [`u64`:`htlc_msat`]

The `payment_hash` is unknown to the final node or the amount for that
`payment_hash` is incorrect.

Note: Originally PERM|16 (`incorrect_payment_amount`) was
used to differentiate incorrect final amount from unknown payment
hash. Sadly, sending this response allows for probing attacks whereby a node
which receives an HTLC for forwarding can check guesses as to its final
destination by sending payments with the same hash but much lower values to
potential destinations and check the response.

1. type: 17 (`final_expiry_too_soon`)

The CLTV expiry is too close to the current block height for safe
handling by the final node.
* [`u32`:`height`]

The `payment_hash` is unknown to the final node, the amount for that
`payment_hash` is incorrect or the CLTV expiry of the htlc is too close to the
current block height for safe handling.

The `htlc_msat` parameter is superfluous, but left in for backwards
compatibility. The value of `htlc_msat` always matches the amount specified in
the final hop onion payload. It therefore does not have any informative value to
the sender. A penultimate hop sending a different amount or expiry for the htlc
is handled through `final_incorrect_cltv_expiry` and
`final_incorrect_htlc_amount`.

The `height` parameter is set by the final node to the best known block height
at the time of receiving the htlc. This can be used by the sender to distinguish
between sending a payment with the wrong final CLTV expiry and an intermediate
hop delaying the payment so that the receiver's invoice CLTV delta requirement
is no longer met.

Note: Originally PERM|16 (`incorrect_payment_amount`) and PERM|17
(`final_expiry_too_soon`) were used to differentiate incorrect htlc parameters
from unknown payment hash. Sadly, sending this response allows for probing
attacks whereby a node which receives an HTLC for forwarding can check guesses
as to its final destination by sending payments with the same hash but much
lower values or expiry heights to potential destinations and check the response.

1. type: 18 (`final_incorrect_cltv_expiry`)
2. data:
Expand Down Expand Up @@ -942,7 +952,7 @@ An _intermediate hop_ MUST NOT, but the _final node_:
altering the amount while not allowing for accidental gross overpayment.
- if the `cltv_expiry` value is unreasonably near the present:
- MUST fail the HTLC.
- MUST return a `final_expiry_too_soon` error.
- MUST return an `incorrect_or_unknown_payment_details` error.
- if the `outgoing_cltv_value` does NOT correspond with the `cltv_expiry` from
the final node's HTLC:
- MUST return `final_incorrect_cltv_expiry` error.
Expand Down