lightning-createonion -- Low-level command to create a custom onion

SYNOPSIS

createonion hops assocdata [session_key] [onion_size]

DESCRIPTION

The createonion RPC command allows the caller to create a custom onion with custom payloads at each hop in the route. A custom onion can be used to implement protocol extensions that are not supported by Core Lightning directly.

The hops parameter is a JSON list of dicts, each specifying a node and the payload destined for that node. The following is an example of a 3 hop onion:

[
    {
        "pubkey": "022d223620a359a47ff7f7ac447c85c46c923da53389221a0054c11c1e3ca31d59",
        "payload": "11020203e904017b06080000670000010001"
    }, {
        "pubkey": "035d2b1192dfba134e10e540875d366ebc8bc353d5aa766b80c090b39c3a5d885d",
        "payload": "11020203e804017506080000670000030001"
    }, {
        "pubkey": "0382ce59ebf18be7d84677c2e35f23294b9992ceca95491fcf8a56c6cb2d9de199",
        "payload": "07020203e8040175"
    }
]

The hops parameter is very similar to the result from getroute however it needs to be modified slightly. The following is the getroute response from which the above hops parameter was generated:

[
    {
        "id": "022d223620a359a47ff7f7ac447c85c46c923da53389221a0054c11c1e3ca31d59",
        "channel": "103x2x1",
        "direction": 1,
        "msatoshi": 1002,
        "amount_msat": "1002msat",
        "delay": 21,
    }, {
        "id": "035d2b1192dfba134e10e540875d366ebc8bc353d5aa766b80c090b39c3a5d885d",
        "channel": "103x1x1",
        "direction": 0,
        "msatoshi": 1001,
        "amount_msat": "1001msat",
        "delay": 15,
    }, {
        "id": "0382ce59ebf18be7d84677c2e35f23294b9992ceca95491fcf8a56c6cb2d9de199",
        "channel": "103x3x1",
        "direction": 0,
        "msatoshi": 1000,
        "amount_msat": "1000msat",
        "delay": 9,
    }
]

Notice that the payload in the hops parameter is the hex-encoded TLV of the parameters in the getroute response, with length prepended as a bigsize_t.
Except for the pubkey, the values are shifted left by one, i.e., the 1st payload in createonion corresponds to the 2nd set of values from getroute.
The final payload is a copy of the last payload sans channel

These rules are directly derived from the onion construction. Please refer BOLT 04 for details and rationale.

The assocdata parameter specifies the associated data that the onion should commit to. If the onion is to be used to send a payment later it MUST match the payment_hash of the payment in order to be valid.

The optional session_key parameter can be used to specify a secret that is used to generate the shared secrets used to encrypt the onion for each hop. It should only be used for testing or if a specific shared secret is important. If not specified it will be securely generated internally, and the shared secrets will be returned.

The optional onion_size parameter specifies a size different from the default payment onion (1300 bytes). May be used for custom protocols like trampoline routing.

RETURN VALUE

On success, an object is returned, containing:

onion (hex): the onion packet (onion_size bytes)
shared_secrets (array of secrets): one shared secret for each node in the hops parameter:
the shared secret with this hop

EXAMPLE

The following example is the result of calling createonion with the above hops parameter:

{
    "onion": "0003f3f80d2142b953319336d2fe4097[...]6af33fcf4fb113bce01f56dd62248a9e5fcbbfba35c",
    "shared_secrets": [
        "88ce98c73e4d9293ab1797b0a913fe9bca0213a566252047d01b8af6da871f3e",
        "4474d296810e57bd460ef8b83d2e7d288321f8a99ff7686f87384699747bcfc4",
        "2a862e4123e01799a732be487fbce297f7dc7cc1467e410f18369cfee476adc2"
    ]
}

The onion corresponds to 1366 hex-encoded bytes. Each shared secret consists of 32 hex-encoded bytes. Both arguments can be passed on to sendonion.

AUTHOR

Christian Decker <decker.christian@gmail.com> is mainly responsible.

RESOURCES

Main web site: https://github.com/ElementsProject/lightning