BOLT 4 - onion routing protocol
2022-03-17 · 2 min read
- Origin Node
- Intermediate Node, a.k.a. Hop
- Final Node
- Route: list of Hops, constructed by Origin Node
- Route payment HTLC from origin node to final node via many intermediate nodes.
- Based on (2009) Sphinx - A Compact and Provably Secure Mix Format (co-authored by old colleague George Danezis :)), extended with a per-hop payload.
- Intermediate nodes can't learn (1) origin, (2) other hops (except pred- and succ- hops), (3) route length, or (4) position in route.
- Origin node must pre-compute full route. Must learn pubkey of each intermediate (and final) node.
- Intermediate nodes advertise their fee schema.
- Fees are just (flat base rate + proportional rate).
- If nodes advertise new fee rates, they must continue to accept their stale fee rates for a little while longer to account for propagation delay.
- Origin node also effectively decides the fee each hop will pay. If an intermediate node deviates (forwards less than advertised) then subsequent nodes must reject.
- Each hop sees a hop payload consisting of
- (1) amount to forward: u64
- (2) outgoing cltv value: u32
- (3) short channel id
- (4) payment data: (payment secret, total msat)
- (5): payment metadata: bytes