为什么闪电网络上HTLC的并发数量被限制为483个？

一、闪电网络白皮书上的描述

• 闪电网络白皮书
• 闪电网络上HTLC并发数量描述：
  

二、从交易罚款的角度解释HTLC的并发数量限制

Penalty Transactions Weight Calculation （网址）

• 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
  

• 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.
• 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.

三、自我总结

• 为了确保在出现问题时可以广播罚款交易，必须限制并发的HTLC数量。
• HTLC最大并发数量计算公式：

  max_num_htlcs = (400000 - 324 - 272 - (4 * 53) - 2) / 413 = 966
  

  • 4000000： maximum Bitcoin block size limit （比特币区块大小限制）
  • 400000：limit for a transaction to be standard （闪电网络上交易标准对数据大小的限制）
  • 324：to_local_penalty_input_weight
  • 272：to_remote output
  • 53：non-witness data
  • 2：witness header
  • 413：HTLC大小
  • 交易数据减去一些必须的数据量，然后除以HTLC大小得到HTLC 可运行的最大数量，由于HTLC是双向传递，所以结果除以二，得到最大并行HTLC数量。

标签：transaction,bytes,penalty,并发,input,483,witness,HTLC
来源： https://blog.csdn.net/m0_46501404/article/details/116132669