1. 引言
在比特币闪电网络协议中，dust_limit_satoshis设置了不会提交到比特币链上的transaction output。
在比特币共识网络中并没有规定低于某dust阈值的output将为invalid或unspendable，但是，在很多流行的比特币实现中，有阻止包含低于dust阈值的交易转发。
Bitcoin Core中定义了如下dust阈值：【基于Bitcoin Core实现中设置的3000 sat/kB feerate】
- pay to pubkey hash (p2pkh): 546 satoshis
- pay to script hash (p2sh): 540 satoshis
- pay to witness pubkey hash (p2wpkh): 294 satoshis
- pay to witness script hash (p2wsh): 330 satoshis
- unknown segwit versions: 354 satoshis
2. Pay to pubkey hash (p2pkh)
A p2pkh output is 34 bytes:
- 8 bytes for the output amount
- 1 byte for the script length
- 25 bytes for the script (OP_DUP OP_HASH160 20 20-bytes OP_EQUALVERIFY OP_CHECKSIG)
A p2pkh input is at least 148 bytes:
- 36 bytes for the previous output (32 bytes hash + 4 bytes index)
- 4 bytes for the sequence
- 1 byte for the script sig length
- 107 bytes for the script sig:
- 1 byte for the items count
- 1 byte for the signature length
- 71 bytes for the signature
- 1 byte for the public key length
- 33 bytes for the public key
The p2pkh dust threshold is then (34 + 148) * 3000 / 1000 = 546 satoshis。
3. Pay to script hash (p2sh)
A p2sh output is 32 bytes:
- 8 bytes for the output amount
- 1 byte for the script length
- 23 bytes for the script (OP_HASH160 20 20-bytes OP_EQUAL)
A p2sh input doesn’t have a fixed size, since it depends on the underlying script, so we use 148 bytes as a lower bound.
The p2sh dust threshold is then (32 + 148) * 3000 / 1000 = 540 satoshis。
4. Pay to witness pubkey hash (p2wpkh)
A p2wpkh output is 31 bytes:
- 8 bytes for the output amount
- 1 byte for the script length
- 22 bytes for the script (OP_0 20 20-bytes)
A p2wpkh input is at least 67 bytes (depending on the signature length):
- 36 bytes for the previous output (32 bytes hash + 4 bytes index)
- 4 bytes for the sequence
- 1 byte for the script sig length
- 26 bytes for the witness (rounded down from 26.75, with the 75% segwit discount applied):
- 1 byte for the items count
- 1 byte for the signature length
- 71 bytes for the signature
- 1 byte for the public key length
- 33 bytes for the public key
The p2wpkh dust threshold is then (31 + 67) * 3000 / 1000 = 294 satoshis
5. Pay to witness script hash (p2wsh)
A p2wsh output is 43 bytes:
- 8 bytes for the output amount
- 1 byte for the script length
- 34 bytes for the script (OP_0 32 32-bytes)
A p2wsh input doesn’t have a fixed size, since it depends on the underlying script, so we use 67 bytes as a lower bound.
The p2wsh dust threshold is then (43 + 67) * 3000 / 1000 = 330 satoshis
6. Unknown segwit versions
Unknown segwit outputs are at most 51 bytes:
- 8 bytes for the output amount
- 1 byte for the script length
- 42 bytes for the script (OP_1 through OP_16 inclusive, followed by a single push of 2 to 40 bytes)
The input doesn’t have a fixed size, since it depends on the underlying script, so we use 67 bytes as a lower bound.
The unknown segwit version dust threshold is then (51 + 67) * 3000 / 1000 = 354 satoshis
7. 闪电网络中commitment transaction的expected weight
闪电网络中commitment transaction的expected weight计算方式为：
p2wsh: 34 bytes
- OP_0: 1 byte
- OP_DATA: 1 byte (witness_script_SHA256 length)
- witness_script_SHA256: 32 bytes
p2wpkh: 22 bytes
- OP_0: 1 byte
- OP_DATA: 1 byte (public_key_HASH160 length)
- public_key_HASH160: 20 bytes
multi_sig: 71 bytes
- OP_2: 1 byte
- OP_DATA: 1 byte (pub_key_alice length)
- pub_key_alice: 33 bytes
- OP_DATA: 1 byte (pub_key_bob length)
- pub_key_bob: 33 bytes
- OP_2: 1 byte
- OP_CHECKMULTISIG: 1 byte
witness: 222 bytes
- number_of_witness_elements: 1 byte
- nil_length: 1 byte
- sig_alice_length: 1 byte
- sig_alice: 73 bytes
- sig_bob_length: 1 byte
- sig_bob: 73 bytes
- witness_script_length: 1 byte
- witness_script (multi_sig)
funding_input: 41 bytes
- previous_out_point: 36 bytes
- hash: 32 bytes
- index: 4 bytes
- var_int: 1 byte (script_sig length)
- script_sig: 0 bytes
- witness <---- "witness" is used instead of "script_sig" for
transaction validation; however, "witness" is stored
separately, and the cost for its size is smaller. So,
the calculation of ordinary data is separated
from the witness data.
- sequence: 4 bytes
output_paying_to_local: 43 bytes
- value: 8 bytes
- var_int: 1 byte (pk_script length)
- pk_script (p2wsh): 34 bytes
output_paying_to_remote (no option_anchors): 31 bytes
- value: 8 bytes
- var_int: 1 byte (pk_script length)
- pk_script (p2wpkh): 22 bytes
output_paying_to_remote (option_anchors): 43 bytes
- value: 8 bytes
- var_int: 1 byte (pk_script length)
- pk_script (p2wsh): 34 bytes
output_anchor (option_anchors): 43 bytes
- value: 8 bytes
- var_int: 1 byte (pk_script length)
- pk_script (p2wsh): 34 bytes
htlc_output: 43 bytes
- value: 8 bytes
- var_int: 1 byte (pk_script length)
- pk_script (p2wsh): 34 bytes
witness_header: 2 bytes
- flag: 1 byte
- marker: 1 byte
commitment_transaction (no option_anchors): 125 + 43 * num-htlc-outputs bytes
- version: 4 bytes
- witness_header <---- part of the witness data
- count_tx_in: 1 byte
- tx_in: 41 bytes
funding_input
- count_tx_out: 1 byte
- tx_out: 74 + 43 * num-htlc-outputs bytes
output_paying_to_remote,
output_paying_to_local,
....htlc_output's...
- lock_time: 4 bytes
commitment_transaction (option_anchors): 225 + 43 * num-htlc-outputs bytes
- version: 4 bytes
- witness_header <---- part of the witness data
- count_tx_in: 1 byte
- tx_in: 41 bytes
funding_input
- count_tx_out: 3 byte
- tx_out: 172 + 43 * num-htlc-outputs bytes
output_paying_to_remote,
output_paying_to_local,
output_anchor,
output_anchor,
....htlc_output's...
- lock_time: 4 bytes
Multiplying non-witness data by 4 results in a weight of:
// 500 + 172 * num-htlc-outputs weight (no option_anchors)
// 900 + 172 * num-htlc-outputs weight (option_anchors)
commitment_transaction_weight = 4 * commitment_transaction
// 224 weight
witness_weight = witness_header + witness
overall_weight (no option_anchors) = 500 + 172 * num-htlc-outputs + 224 weight
overall_weight (option_anchors) = 900 + 172 * num-htlc-outputs + 224 weight
8. 闪电网络中HTLC-timeout和HTLC-success交易的expected weight
闪电网络中HTLC-timeout和HTLC-success交易的expected weight计算方式为：
accepted_htlc_script: 140 bytes (143 bytes with option_anchors)
- OP_DUP: 1 byte
- OP_HASH160: 1 byte
- OP_DATA: 1 byte (RIPEMD160(SHA256(revocationpubkey)) length)
- RIPEMD160(SHA256(revocationpubkey)): 20 bytes
- OP_EQUAL: 1 byte
- OP_IF: 1 byte
- OP_CHECKSIG: 1 byte
- OP_ELSE: 1 byte
- OP_DATA: 1 byte (remotepubkey length)
- remotepubkey: 33 bytes
- OP_SWAP: 1 byte
- OP_SIZE: 1 byte
- OP_DATA: 1 byte (32 length)
- 32: 1 byte
- OP_EQUAL: 1 byte
- OP_IF: 1 byte
- OP_HASH160: 1 byte
- OP_DATA: 1 byte (RIPEMD160(payment_hash) length)
- RIPEMD160(payment_hash): 20 bytes
- OP_EQUALVERIFY: 1 byte
- 2: 1 byte
- OP_SWAP: 1 byte
- OP_DATA: 1 byte (localpubkey length)
- localpubkey: 33 bytes
- 2: 1 byte
- OP_CHECKMULTISIG: 1 byte
- OP_ELSE: 1 byte
- OP_DROP: 1 byte
- OP_DATA: 1 byte (cltv_expiry length)
- cltv_expiry: 4 bytes
- OP_CHECKLOCKTIMEVERIFY: 1 byte
- OP_DROP: 1 byte
- OP_CHECKSIG: 1 byte
- OP_ENDIF: 1 byte
- OP_1: 1 byte (option_anchors)
- OP_CHECKSEQUENCEVERIFY: 1 byte (option_anchors)
- OP_DROP: 1 byte (option_anchors)
- OP_ENDIF: 1 byte
offered_htlc_script: 133 bytes (136 bytes with option_anchors)
- OP_DUP: 1 byte
- OP_HASH160: 1 byte
- OP_DATA: 1 byte (RIPEMD160(SHA256(revocationpubkey)) length)
- RIPEMD160(SHA256(revocationpubkey)): 20 bytes
- OP_EQUAL: 1 byte
- OP_IF: 1 byte
- OP_CHECKSIG: 1 byte
- OP_ELSE: 1 byte
- OP_DATA: 1 byte (remotepubkey length)
- remotepubkey: 33 bytes
- OP_SWAP: 1 byte
- OP_SIZE: 1 byte
- OP_DATA: 1 byte (32 length)
- 32: 1 byte
- OP_EQUAL: 1 byte
- OP_NOTIF: 1 byte
- OP_DROP: 1 byte
- 2: 1 byte
- OP_SWAP: 1 byte
- OP_DATA: 1 byte (localpubkey length)
- localpubkey: 33 bytes
- 2: 1 byte
- OP_CHECKMULTISIG: 1 byte
- OP_ELSE: 1 byte
- OP_HASH160: 1 byte
- OP_DATA: 1 byte (RIPEMD160(payment_hash) length)
- RIPEMD160(payment_hash): 20 bytes
- OP_EQUALVERIFY: 1 byte
- OP_CHECKSIG: 1 byte
- OP_ENDIF: 1 byte
- OP_1: 1 byte (option_anchors)
- OP_CHECKSEQUENCEVERIFY: 1 byte (option_anchors)
- OP_DROP: 1 byte (option_anchors)
- OP_ENDIF: 1 byte
timeout_witness: 285 bytes (288 bytes with option_anchors)
- number_of_witness_elements: 1 byte
- nil_length: 1 byte
- sig_alice_length: 1 byte
- sig_alice: 73 bytes
- sig_bob_length: 1 byte
- sig_bob: 73 bytes
- nil_length: 1 byte
- witness_script_length: 1 byte
- witness_script (offered_htlc_script)
success_witness: 324 bytes (327 bytes with option_anchors)
- number_of_witness_elements: 1 byte
- nil_length: 1 byte
- sig_alice_length: 1 byte
- sig_alice: 73 bytes
- sig_bob_length: 1 byte
- sig_bob: 73 bytes
- preimage_length: 1 byte
- preimage: 32 bytes
- witness_script_length: 1 byte
- witness_script (accepted_htlc_script)
commitment_input: 41 bytes
- previous_out_point: 36 bytes
- hash: 32 bytes
- index: 4 bytes
- var_int: 1 byte (script_sig length)
- script_sig: 0 bytes
- witness (success_witness or timeout_witness)
- sequence: 4 bytes
htlc_output: 43 bytes
- value: 8 bytes
- var_int: 1 byte (pk_script length)
- pk_script (p2wsh): 34 bytes
htlc_transaction:
- version: 4 bytes
- witness_header <---- part of the witness data
- count_tx_in: 1 byte
- tx_in: 41 bytes
commitment_input
- count_tx_out: 1 byte
- tx_out: 43
htlc_output
- lock_time: 4 bytes
Multiplying non-witness data by 4 results in a weight of 376. Adding the witness data for each case (285 or 288 + 2 for HTLC-timeout, 324 or 327 + 2 for HTLC-success) results in weights of:
663 (HTLC-timeout) (666 with option_anchors))
703 (HTLC-success) (706 with option_anchors))
- (really 702 and 705, but we use these numbers for historical reasons)