lnd/docs/zero_conf_channels.md

Setting up zero-conf channels in LND

Zero-conf channels are channels that do not require confirmations to be used. Because of this, the fundee must trust the funder to not double-spend the channel and steal the balance of the channel.

Startup

Two options must be specified either on the command line or in the config file:

• protocol.option-scid-alias
• protocol.zero-conf

If one of these is missing, zero-conf channels won't work. This applies for both the funder and fundee.

Opening the channel

The channel open flow is slightly different, so there are new requirements for the initiator and responder in the funding flow.

Initiator requirements

When opening the channel, the initiator must ensure that the anchors channel_type is enabled. Additionally, the initiator must specify on the openchannel command line call or the corresponding RPC that the zero-conf flag is set.

Responder requirements

The responder flow is different from the initiator's. If the responder has not specified a ChannelAcceptor, then ALL open channel requests will be failed regardless if they are zero-conf or not. The ChannelAcceptor RPC will give the responder information on whether the initiator is requesting a zero-conf channel via the channel type.

If the responder has specified a ChannelAcceptor and the funder has set the zero-conf channel type, then the responder should set the ZeroConf flag to true if they wish to accept it and false otherwise. If ZeroConf is true, then MinAcceptDepth should be zero.

It is possible for the responder to set the ZeroConf flag to true even when the funder did not specify the zero-conf channel type. This will only create a zero-conf channel if the funder is a non-LND node that supports this behavior. This is for compatibility with LDK nodes. In this case, the responder must know that the funder is using an implementation that supports this behavior (like LDK). The scid-alias feature bit must also have been negotiated.

Updated RPC calls

The listchannels and closedchannels RPC calls have been updated. They now include a list of all aliases that the channel has used. The ChanId in the response is the confirmed SCID for non-zero-conf channels. For zero-conf channels, the ChanID is the first alias used in the channel. The RPCs will also return the confirmed SCID for zero-conf channels in a separate field.

A new RPC listaliases has been introduced. It returns a set of mappings from one SCID to a list of SCIDS. The key is the confirmed SCID for non-zero-conf channels. For zero-conf channels, it is the first alias used in the channel. The values are the list of all aliases ever used in the channel (including the key for zero-conf channels). This information can be cross-referenced with the output of listchannels and closedchannels to determine what channel a particular alias belongs to.