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There are three different scripts for penalty transactions, with the following witness weights：
to_local_penalty_witness: 160 bytes
offered_htlc_penalty_witness: 243 bytes
accepted_htlc_penalty_witness: 249 bytes
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The penalty txinput itself takes up 41 bytes and has a weight of 164 bytes, which results in the following weights for each input:
to_local_penalty_input_weight: 324 bytes
offered_htlc_penalty_input_weight: 407 bytes
accepted_htlc_penalty_input_weight: 413 bytes
- The rest of the penalty transaction takes up 4+1+1+8+1+34+4=53 bytes of non-witness data: assuming it has a pay-to-witness-script-hash (the largest standard output script), in addition to a 2-byte witness header.
- n addition to spending these outputs, a penalty transaction may optionally spend the commitment transaction’s to_remote output (e.g. to reduce the total amount paid in fees). Doing so requires the inclusion of a P2WPKH witness and an additional txinput, resulting in an additional 108 + 164 = 272 bytes.
- In the worst case scenario, the node holds only incoming HTLCs, and the HTLC-timeout transactions are not published, which forces the node to spend from the commitment transaction.
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With a maximum standard weight of 400000 bytes, the maximum number of HTLCs that can be swept in a single transaction is as follows:
max_num_htlcs = (400000 - 324 - 272 - (4 * 53) - 2) / 413 = 966
- Thus, 483 bidirectional HTLCs (containing both to_local and to_remote outputs) can be resolved in a single penalty transaction. Note: even if the to_remote output is not swept, the resulting max_num_htlcs is 967; which yields the same unidirectional limit of 483 HTLCs.