[Lightning-dev] [PATCH] First draft of option_simplfied_commitment

Matt Corallo lf-lists at mattcorallo.com
Wed Nov 21 17:55:33 UTC 2018


Oh, also, obviously, the HTLC transactions need a pushme output, though 
luckily only one for the side we expect to be broadcasting the transaction.

On 11/21/18 2:54 AM, Matt Corallo wrote:
> Not sure if others already realized this, but in thinking about our RBF 
> policy hack from Adelaide a bit more, to allow the carve-out exception 
> of "last tx in a package, which has only one unconfirmed ancestor" to 
> always be available for the "honest party" when broadcasting a 
> commitment transaction, we also need at least a CSV delay of 1 block on 
> the HTLC transaction outputs (as otherwise those transactions could 
> count as the carve-out tx).
> 
> Matt
> 
> On 11/21/18 2:17 AM, Rusty Russell wrote:
>> I'm also starting to implement this, to see what I missed!
>>
>> Original at https://github.com/lightningnetwork/lightning-rfc/pull/513
>>
>> Pasted here for your reading convenience:
>>
>> - Option is sticky; it set at open time, it stays with channel
>>    - I didn't want to have to handle penalty txs on channels which switch
>>    - We could, however, upgrade on splice.
>> - Feerate is fixed at 253
>>    - `feerate_per_kw` is still in open /accept (just ignored): 
>> multifund may want it.
>> - closing tx negotiates *upwards* not *downwards*
>>    - Starting from base fee of commitment tx = 282 satoshi.
>> - to_remote output is always CSV delayed.
>> - pushme outputs are paid for by funder, but only exist if the matching
>>    to_local/remote output exists.
>> - After 10 blocks, they become anyone-can-spend (they need to see the
>>    to-local/remote witness script though).
>> - remotepubkey is not rotated.
>> - You must spend your pushme output; you may sweep for others.
>>
>> Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
>>
>> diff --git a/02-peer-protocol.md b/02-peer-protocol.md
>> index 7cf9ebf..6ec1155 100644
>> --- a/02-peer-protocol.md
>> +++ b/02-peer-protocol.md
>> @@ -133,7 +133,9 @@ node can offer.
>>   (i.e. 1/4 the more normally-used 'satoshi per 1000 vbytes') that this
>>   side will pay for commitment and HTLC transactions, as described in
>>   [BOLT #3](03-transactions.md#fee-calculation) (this can be adjusted
>> -later with an `update_fee` message).
>> +later with an `update_fee` message).  Note that if
>> +`option_simplified_commitment` is negotiated, this `feerate_per_kw`
>> +is treated as 253 for all transactions.
>>   `to_self_delay` is the number of blocks that the other node's to-self
>>   outputs must be delayed, using `OP_CHECKSEQUENCEVERIFY` delays; this
>> @@ -208,7 +210,8 @@ The receiving node MUST fail the channel if:
>>     - `push_msat` is greater than `funding_satoshis` * 1000.
>>     - `to_self_delay` is unreasonably large.
>>     - `max_accepted_htlcs` is greater than 483.
>> -  - it considers `feerate_per_kw` too small for timely processing or 
>> unreasonably large.
>> +  - if `option_simplified_commitment` is not negotiated:
>> +    - it considers `feerate_per_kw` too small for timely processing 
>> or unreasonably large.
>>     - `funding_pubkey`, `revocation_basepoint`, `htlc_basepoint`, 
>> `payment_basepoint`, or `delayed_payment_basepoint`
>>   are not valid DER-encoded compressed secp256k1 pubkeys.
>>     - `dust_limit_satoshis` is greater than `channel_reserve_satoshis`.
>> @@ -228,7 +231,7 @@ The *channel reserve* is specified by the peer's 
>> `channel_reserve_satoshis`: 1%
>>   The sender can unconditionally give initial funds to the receiver 
>> using a non-zero `push_msat`, but even in this case we ensure that the 
>> funder has sufficient remaining funds to pay fees and that one side 
>> has some amount it can spend (which also implies there is at least one 
>> non-dust output). Note that, like any other on-chain transaction, this 
>> payment is not certain until the funding transaction has been 
>> confirmed sufficiently (with a danger of double-spend until this 
>> occurs) and may require a separate method to prove payment via 
>> on-chain confirmation.
>> -The `feerate_per_kw` is generally only of concern to the sender (who 
>> pays the fees), but there is also the fee rate paid by HTLC 
>> transactions; thus, unreasonably large fee rates can also penalize the 
>> recipient.
>> +The `feerate_per_kw` is generally only of concern to the sender (who 
>> pays the fees), but there is also the fee rate paid by HTLC 
>> transactions; thus, unreasonably large fee rates can also penalize the 
>> recipient.  It is ignored for `option_simplified_commitment`.
>>   Separating the `htlc_basepoint` from the `payment_basepoint` 
>> improves security: a node needs the secret associated with the 
>> `htlc_basepoint` to produce HTLC signatures for the protocol, but the 
>> secret for the `payment_basepoint` can be in cold storage.
>> @@ -340,6 +343,12 @@ This message introduces the `channel_id` to 
>> identify the channel. It's derived f
>>   #### Requirements
>> +Both peers:
>> +  - if `option_simplified_commitment` was negotiated:
>> +    - `option_simplified_commitment` applies to all commitment and 
>> HTLC transactions
>> +  - otherwise:
>> +    - `option_simplified_commitment` does not apply to any commitment 
>> or HTLC transactions
>> +
>>   The sender MUST set:
>>     - `channel_id` by exclusive-OR of the `funding_txid` and the 
>> `funding_output_index` from the `funding_created` message.
>>     - `signature` to the valid signature, using its `funding_pubkey` 
>> for the initial commitment transaction, as defined in [BOLT 
>> #3](03-transactions.md#commitment-transaction).
>> @@ -351,6 +360,12 @@ The recipient:
>>     - on receipt of a valid `funding_signed`:
>>       - SHOULD broadcast the funding transaction.
>> +#### Rationale
>> +
>> +We decide on `option_simplified_commitment` at this point when we 
>> first have to generate the commitment
>> +transaction.  Even if a later reconnection does not negotiate this 
>> parameter, this channel will honor it.
>> +This simplifies channel state, particularly penalty transaction 
>> handling.
>> +
>>   ### The `funding_locked` Message
>>   This message indicates that the funding transaction has reached the 
>> `minimum_depth` asked for in `accept_channel`. Once both nodes have 
>> sent this, the channel enters normal operating mode.
>> @@ -508,8 +523,11 @@ The funding node:
>>       - SHOULD send a `closing_signed` message.
>>   The sending node:
>> -  - MUST set `fee_satoshis` less than or equal to the
>> - base fee of the final commitment transaction, as calculated in [BOLT 
>> #3](03-transactions.md#fee-calculation).
>> +  - if `option_upfront_shutdown_script` applies to the final 
>> commitment transaction:
>> +    - MUST set `fee_satoshis` greater than or equal to 282.
>> +  - otherwise:
>> +    - MUST set `fee_satoshis` less than or equal to the
>> +      base fee of the final commitment transaction, as calculated in 
>> [BOLT #3](03-transactions.md#fee-calculation).
>>     - SHOULD set the initial `fee_satoshis` according to its
>>    estimate of cost of inclusion in a block.
>>     - MUST set `signature` to the Bitcoin signature of the close
>> @@ -543,9 +561,18 @@ progress is made, even if only by a single 
>> satoshi at a time. To avoid
>>   keeping state and to handle the corner case, where fees have shifted
>>   between disconnection and reconnection, negotiation restarts on 
>> reconnection.
>> -Note there is limited risk if the closing transaction is
>> -delayed, but it will be broadcast very soon; so there is usually no
>> -reason to pay a premium for rapid processing.
>> +In the `option_simplified_commitment` case, the fees on the commitment
>> +transaction itself are minimal (it is assumed that a child 
>> transaction will
>> +supply additional fee incentive), so that forms a floor for negotiation.
>> +[BOLT #3](03-transactions.md#fee-calculation), gives 282 satoshis (1116
>> +weight, 254 `feerate_per_kw`).
>> +
>> +Otherwise, the commitment transaction usually pays a premium fee, so 
>> that
>> +forms a ceiling.
>> +
>> +Note there is limited risk if the closing transaction is delayed, but 
>> it will
>> +be broadcast very soon; so there is usually no reason to pay a 
>> premium for
>> +rapid processing.
>>   ## Normal Operation
>> @@ -763,7 +790,10 @@ is destined, is described in [BOLT 
>> #4](04-onion-routing.md).
>>   A sending node:
>>     - MUST NOT offer `amount_msat` it cannot pay for in the
>>   remote commitment transaction at the current `feerate_per_kw` (see 
>> "Updating
>> -Fees") while maintaining its channel reserve.
>> +Fees") while maintaining its channel reserve
>> +  - if `option_simplified_commitment` applies to this commitment 
>> transaction and the sending
>> +    node is the funder:
>> +    - MUST be able to additionally pay for `to_local_pushme` and 
>> `to_remote_pushme` above its reserve.
>>     - MUST offer `amount_msat` greater than 0.
>>     - MUST NOT offer `amount_msat` below the receiving node's 
>> `htlc_minimum_msat`
>>     - MUST set `cltv_expiry` less than 500000000.
>> @@ -782,7 +812,7 @@ Fees") while maintaining its channel reserve.
>>   A receiving node:
>>     - receiving an `amount_msat` equal to 0, OR less than its own 
>> `htlc_minimum_msat`:
>>       - SHOULD fail the channel.
>> -  - receiving an `amount_msat` that the sending node cannot afford at 
>> the current `feerate_per_kw` (while maintaining its channel reserve):
>> +  - receiving an `amount_msat` that the sending node cannot afford at 
>> the current `feerate_per_kw` (while maintaining its channel reserve 
>> and any `to_local_pushme` and `to_remote_pushme` fees):
>>       - SHOULD fail the channel.
>>     - if a sending node adds more than its `max_accepted_htlcs` HTLCs to
>>       its local commitment transaction, OR adds more than its 
>> `max_htlc_value_in_flight_msat` worth of offered HTLCs to its local 
>> commitment transaction:
>> @@ -997,6 +1027,11 @@ A node:
>>   ### Updating Fees: `update_fee`
>> +If `option_simplified_commitment` applies to the commitment transaction,
>> +`update_fee` is never used: the `feerate_per_kw` is always considered 
>> 253, but
>> +the funder also pays 2000 satoshi for the `to_local_pushme` and
>> +`to_remote_pushme` outputs.
>> +
>>   An `update_fee` message is sent by the node which is paying the
>>   Bitcoin fee. Like any update, it's first committed to the receiver's
>>   commitment transaction and then (once acknowledged) committed to the
>> @@ -1020,13 +1055,19 @@ given in [BOLT 
>> #3](03-transactions.md#fee-calculation).
>>   #### Requirements
>>   The node _responsible_ for paying the Bitcoin fee:
>> -  - SHOULD send `update_fee` to ensure the current fee rate is 
>> sufficient (by a
>> +  - if `option_simplified_commitment` applies to the commitment 
>> transaction:
>> +    - MUST NOT send `update_fee`.
>> +  - otherwise:
>> +    - SHOULD send `update_fee` to ensure the current fee rate is 
>> sufficient (by a
>>         significant margin) for timely processing of the commitment 
>> transaction.
>>   The node _not responsible_ for paying the Bitcoin fee:
>>     - MUST NOT send `update_fee`.
>>   A receiving node:
>> +  - if `option_simplified_commitment` applies to the commitment 
>> transaction:
>> +    - SHOULD fail the channel.
>> +    - MUST NOT update the `feerate_per_kw`.
>>     - if the `update_fee` is too low for timely processing, OR is 
>> unreasonably large:
>>       - SHOULD fail the channel.
>>     - if the sender is not responsible for paying the Bitcoin fee:
>> @@ -1038,7 +1079,12 @@ A receiving node:
>>   #### Rationale
>> -Bitcoin fees are required for unilateral closes to be effective —
>> +Fee adjustments are unnecessary for `option_simplified_commitment` which
>> +relies on "pushme" outputs and a child transaction which will provide
>> +additional fee incentive which can be calculated at the time it is 
>> spent, and
>> +replaced by higher-fee children if required.
>> +
>> +Without this option, bitcoin fees are required for unilateral closes 
>> to be effective —
>>   particularly since there is no general method for the broadcasting 
>> node to use
>>   child-pays-for-parent to increase its effective fee.
>> diff --git a/03-transactions.md b/03-transactions.md
>> index e769961..440bd0d 100644
>> --- a/03-transactions.md
>> +++ b/03-transactions.md
>> @@ -82,6 +82,8 @@ To allow an opportunity for penalty transactions, in 
>> case of a revoked commitmen
>>   The reason for the separate transaction stage for HTLC outputs is so 
>> that HTLCs can timeout or be fulfilled even though they are within the 
>> `to_self_delay` delay.
>>   Otherwise, the required minimum timeout on HTLCs is lengthened by 
>> this delay, causing longer timeouts for HTLCs traversing the network.
>> +If `option_simplified_commitment` applies to the commitment 
>> transaction, then the `to_self_delay` used for all transactions is the 
>> greater of the `to_self_delay` sent by each peer.  Otherwise, each 
>> peer sends the `to_self_delay` to be used for the other peer's 
>> commitment amd HTLC transactions.
>> +
>>   The amounts for each output MUST be rounded down to whole satoshis. 
>> If this amount, minus the fees for the HTLC transaction, is less than 
>> the `dust_limit_satoshis` set by the owner of the commitment 
>> transaction, the output MUST NOT be produced (thus the funds add to 
>> fees).
>>   #### `to_local` Output
>> @@ -109,7 +111,40 @@ If a revoked commitment transaction is published, 
>> the other party can spend this
>>   #### `to_remote` Output
>> -This output sends funds to the other peer and thus is a simple P2WPKH 
>> to `remotepubkey`.
>> +This output sends funds to the other peer, thus is not encumbered by a
>> +revocation private key.
>> +
>> +If `option_simplified_commitment` applies to the commitment 
>> transaction, the `to_remote` output is delayed similarly to the 
>> `to_local` output, and is to a fixed key:
>> +
>> +        `to_self_delay`
>> +        OP_CSV
>> +        OP_DROP
>> +        <remote_pubkey>
>> +
>> +The output is spent by a transaction with `nSequence` field set to 
>> `to_self_delay` (which can only be valid after that duration has 
>> passed) and witness:
>> +
>> +    <remote_sig>
>> +
>> +Otherwise, this output is a simple P2WPKH to `remotepubkey`.
>> +
>> +
>> +#### `to_local_pushme` and `to_remote_pushme` Output 
>> (option_simplified_commitment)
>> +
>> +This output can be spent by the local and remote nodes respectivey to 
>> provide incentive to mine the transaction, using 
>> child-pays-for-parent.  They are only added if the `to_local` and 
>> `to_remote` outputs exist, respectively.
>> +
>> +    OP_DEPTH
>> +    OP_IF
>> +        <pubkey> OP_CHECKSIG
>> +    OP_ELSE
>> +        10 OP_CSV
>> +    OP_ENDIF
>> +
>> +The `<pubkey>` is `<local_delayedpubkey>` to `to_local_pushme` and
>> +`<remote_delayedpubkey>` for `to_remote_pushme`.  The output amount is
>> +1000 satoshi, to encourage spending of the output.  Once the
>> +`remote_pubkey` is revealed (by spending the `to_local` output) and
>> +the commitment transaction is 10 blocks deep, anyone can spend it.
>> +
>>   #### Offered HTLC Outputs
>> @@ -294,6 +329,9 @@ The fee calculation for both commitment 
>> transactions and HTLC
>>   transactions is based on the current `feerate_per_kw` and the
>>   *expected weight* of the transaction.
>> +Note that if `option_simplified_commitment` applies to the commitment
>> +transaction then `feerate_per_kw` is 253.
>> +
>>   The actual and expected weights vary for several reasons:
>>   * Bitcoin uses DER-encoded signatures, which vary in size.
>> @@ -306,10 +344,12 @@ Thus, a simplified formula for *expected weight* 
>> is used, which assumes:
>>   * Signatures are 73 bytes long (the maximum length).
>>   * There are a small number of outputs (thus 1 byte to count them).
>>   * There are always both a `to_local` output and a `to_remote` output.
>> +* (if `option_simplified_commitment`) there are always both a 
>> `to_local_pushme` and `to_remote_pushme` output.
>>   This yields the following *expected weights* (details of the 
>> computation in [Appendix A](#appendix-a-expected-weights)):
>> -    Commitment weight:   724 + 172 * num-untrimmed-htlc-outputs
>> +    Commitment weight (no option_simplified_commitment):   724 + 172 
>> * num-untrimmed-htlc-outputs
>> +    Commitment weight (option_simplified_commitment:  1116 + 172 * 
>> num-untrimmed-htlc-outputs
>>       HTLC-timeout weight: 663
>>       HTLC-success weight: 703
>> @@ -366,7 +406,7 @@ outputs) is 7140 satoshi. The final fee may be 
>> even higher if the
>>   ### Fee Payment
>> -Base commitment transaction fees are extracted from the funder's 
>> amount; if that amount is insufficient, the entire amount of the 
>> funder's output is used.
>> +Base commitment transaction fees and amounts for `to_local_pushme` 
>> and `to_remote_pushme` outputs are extracted from the funder's amount; 
>> if that amount is insufficient, the entire amount of the funder's 
>> output is used.
>>   Note that after the fee amount is subtracted from the to-funder output,
>>   that output may be below `dust_limit_satoshis`, and thus will also
>> @@ -390,23 +430,29 @@ committed HTLCs:
>>   2. Calculate the base [commitment transaction fee](#fee-calculation).
>>   3. Subtract this base fee from the funder (either `to_local` or 
>> `to_remote`),
>>      with a floor of 0 (see [Fee Payment](#fee-payment)).
>> +4. If `option_simplified_commitment` applies to the commitment 
>> transaction,
>> +   subtract 2000 satoshis from the funder (either `to_local` or 
>> `to_remote`).
>>   3. For every offered HTLC, if it is not trimmed, add an
>>      [offered HTLC output](#offered-htlc-outputs).
>>   4. For every received HTLC, if it is not trimmed, add an
>>      [received HTLC output](#received-htlc-outputs).
>>   5. If the `to_local` amount is greater or equal to 
>> `dust_limit_satoshis`,
>>      add a [`to_local` output](#to_local-output).
>> +6. If `option_simplified_commitment` applies to the commitment 
>> transaction,
>> +   and `to_local` was added, add `to_local_pushme`.
>>   6. If the `to_remote` amount is greater or equal to 
>> `dust_limit_satoshis`,
>>      add a [`to_remote` output](#to_remote-output).
>> +6. If `option_simplified_commitment` applies to the commitment 
>> transaction,
>> +   and `to_remote` was added, add `to_remote_pushme`.
>>   7. Sort the outputs into [BIP 69 
>> order](#transaction-input-and-output-ordering).
>>   # Keys
>>   ## Key Derivation
>> -Each commitment transaction uses a unique set of keys: `localpubkey` 
>> and `remotepubkey`.
>> +Each commitment transaction uses a unique `localpubkey`, and a 
>> `remotepubkey`.
>>   The HTLC-success and HTLC-timeout transactions use 
>> `local_delayedpubkey` and `revocationpubkey`.
>> -These are changed for every transaction based on the 
>> `per_commitment_point`.
>> +These are changed for every transaction based on the 
>> `per_commitment_point`, with the exception of `remotepubkey` if 
>> `option_simplified_commitment` is negotiated.
>>   The reason for key change is so that trustless watching for revoked
>>   transactions can be outsourced. Such a _watcher_ should not be able to
>> @@ -419,8 +465,9 @@ avoid storage of every commitment transaction, a 
>> _watcher_ can be given the
>>   the scripts required for the penalty transaction; thus, a _watcher_ 
>> need only be
>>   given (and store) the signatures for each penalty input.
>> -Changing the `localpubkey` and `remotepubkey` every time ensures that 
>> commitment
>> -transaction ID cannot be guessed; every commitment transaction uses 
>> an ID
>> +Changing the `localpubkey` every time ensures that commitment
>> +transaction ID cannot be guessed except in the trivial case where 
>> there is no
>> +`to_local` output, as every commitment transaction uses an ID
>>   in its output script. Splitting the `local_delayedpubkey`, which is 
>> required for
>>   the penalty transaction, allows it to be shared with the _watcher_ 
>> without
>>   revealing `localpubkey`; even if both peers use the same _watcher_, 
>> nothing is revealed.
>> @@ -434,14 +481,13 @@ For efficiency, keys are generated from a series 
>> of per-commitment secrets
>>   that are generated from a single seed, which allows the receiver to 
>> compactly
>>   store them (see [below](#efficient-per-commitment-secret-storage)).
>> -### `localpubkey`, `remotepubkey`, `local_htlcpubkey`, 
>> `remote_htlcpubkey`, `local_delayedpubkey`, and `remote_delayedpubkey` 
>> Derivation
>> +### `localpubkey``local_htlcpubkey`, `remote_htlcpubkey`, 
>> `local_delayedpubkey`, and `remote_delayedpubkey` Derivation
>>   These pubkeys are simply generated by addition from their base points:
>>       pubkey = basepoint + SHA256(per_commitment_point || basepoint) * G
>> -The `localpubkey` uses the local node's `payment_basepoint`; the 
>> `remotepubkey`
>> -uses the remote node's `payment_basepoint`; the `local_delayedpubkey`
>> +The `localpubkey` uses the local node's `payment_basepoint`; the 
>> `local_delayedpubkey`
>>   uses the local node's `delayed_payment_basepoint`; the 
>> `local_htlcpubkey` uses the
>>   local node's `htlc_basepoint`; and the `remote_delayedpubkey` uses 
>> the remote
>>   node's `delayed_payment_basepoint`.
>> @@ -451,6 +497,17 @@ secrets are known (i.e. the private keys 
>> corresponding to `localpubkey`, `local_
>>       privkey = basepoint_secret + SHA256(per_commitment_point || 
>> basepoint)
>> +### `remotepubkey` Derivation
>> +
>> +If `option_simplified_commitment` is negotiated the `remotepubkey` is 
>> simply the remote node's `payment_basepoint`, otherwise it is 
>> calculated as above using the remote node's `payment_basepoint`.
>> +
>> +The simplified derivation means that a node can spend a commitment
>> +transaction even if it has lost data and doesn't know the
>> +corresponding `payment_basepoint`.  A watchtower could correlate
>> +transactions given to it which only have a `to_remote` output if it
>> +sees one of them onchain, but such transactions do not need any
>> +enforcement and should not be handed to a watchtower.
>> +
>>   ### `revocationpubkey` Derivation
>>   The `revocationpubkey` is a blinded key: when the local node wishes 
>> to create a new
>> @@ -636,12 +693,22 @@ The *expected weight* of a commitment 
>> transaction is calculated as follows:
>>           - var_int: 1 byte (pk_script length)
>>           - pk_script (p2wsh): 34 bytes
>> -    output_paying_to_remote: 31 bytes
>> +    output_paying_to_remote (no option_simplified_commitment): 31 bytes
>>           - value: 8 bytes
>>           - var_int: 1 byte (pk_script length)
>>           - pk_script (p2wpkh): 22 bytes
>> -     htlc_output: 43 bytes
>> +    output_paying_to_remote (option_simplified_commitment): 43 bytes
>> +        - value: 8 bytes
>> +        - var_int: 1 byte (pk_script length)
>> +        - pk_script (p2wsh): 34 bytes
>> +
>> +    output_pushme (option_simplified_commitment): 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
>> @@ -650,7 +717,7 @@ The *expected weight* of a commitment transaction 
>> is calculated as follows:
>>           - flag: 1 byte
>>           - marker: 1 byte
>> -     commitment_transaction: 125 + 43 * num-htlc-outputs bytes
>> +     commitment_transaction (no option_simplified_commitment): 125 + 
>> 43 * num-htlc-outputs bytes
>>           - version: 4 bytes
>>           - witness_header <---- part of the witness data
>>           - count_tx_in: 1 byte
>> @@ -663,15 +730,32 @@ The *expected weight* of a commitment 
>> transaction is calculated as follows:
>>               ....htlc_output's...
>>           - lock_time: 4 bytes
>> +     commitment_transaction (option_simplified_commitment): 223 + 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: 172 + 43 * num-htlc-outputs bytes
>> +            output_paying_to_remote,
>> +            output_paying_to_local,
>> +            output_pushme,
>> +            output_pushme,
>> +            ....htlc_output's...
>> +        - lock_time: 4 bytes
>> +
>>   Multiplying non-witness data by 4 results in a weight of:
>> -    // 500 + 172 * num-htlc-outputs weight
>> +    // 500 + 172 * num-htlc-outputs weight (no 
>> option_simplified_commitment)
>> +    // 892 + 172 * num-htlc-outputs weight 
>> (option_simplified_commitment)
>>       commitment_transaction_weight = 4 * commitment_transaction
>>       // 224 weight
>>       witness_weight = witness_header + witness
>> -    overall_weight = 500 + 172 * num-htlc-outputs + 224 weight
>> +    overall_weight (no option_simplified_commitment) = 500 + 172 * 
>> num-htlc-outputs + 224 weight
>> +    overall_weight (option_simplified_commitment) = 892 + 172 * 
>> num-htlc-outputs + 224 weight
>>   ## Expected Weight of HTLC-timeout and HTLC-success Transactions
>> diff --git a/05-onchain.md b/05-onchain.md
>> index 231c209..c5fb5e1 100644
>> --- a/05-onchain.md
>> +++ b/05-onchain.md
>> @@ -89,21 +89,29 @@ trigger any action.
>>   # Commitment Transaction
>>   The local and remote nodes each hold a *commitment transaction*. 
>> Each of these
>> -commitment transactions has four types of outputs:
>> +commitment transactions has six types of outputs:
>>   1. _local node's main output_: Zero or one output, to pay to the 
>> *local node's*
>> -commitment pubkey.
>> +delayed pubkey.
>>   2. _remote node's main output_: Zero or one output, to pay to the 
>> *remote node's*
>> -commitment pubkey.
>> +pubkey.
>> +1. _local node's push output_: Zero or one output, to pay to the 
>> *local node's*
>> +delayed pubkey.
>> +2. _remote node's push output_: Zero or one output, to pay to the 
>> *remote node's*
>> +pubkey.
>>   3. _local node's offered HTLCs_: Zero or more pending payments 
>> (*HTLCs*), to pay
>>   the *remote node* in return for a payment preimage.
>>   4. _remote node's offered HTLCs_: Zero or more pending payments 
>> (*HTLCs*), to
>>   pay the *local node* in return for a payment preimage.
>>   To incentivize the local and remote nodes to cooperate, an 
>> `OP_CHECKSEQUENCEVERIFY`
>> -relative timeout encumbers the *local node's outputs* (in the *local 
>> node's
>> +relative timeout encumbers some outputs: the *local node's outputs* 
>> (in the *local node's
>>   commitment transaction*) and the *remote node's outputs* (in the 
>> *remote node's
>> -commitment transaction*). So for example, if the local node publishes 
>> its
>> +commitment transaction*). If `option_simplified_commitment` applies
>> +to the commitment transaction, then the *to_remote* output of each 
>> commitment is
>> +identically encumbered, for fairness.
>> +
>> +Without `option_simplified_commitment`, if the local node publishes its
>>   commitment transaction, it will have to wait to claim its own funds,
>>   whereas the remote node will have immediate access to its own funds. 
>> As a
>>   consequence, the two commitment transactions are not identical, but 
>> they are
>> @@ -140,6 +148,11 @@ A node:
>>         - otherwise:
>>           - MUST use the *last commitment transaction*, for which it 
>> has a
>>           signature, to perform a *unilateral close*.
>> +      - MUST spend any `to_local_pushme` output, providing sufficient 
>> fees as incentive to include the commitment transaction in a block
>> +        - SHOULD use 
>> [replace-by-fee](https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki) 
>> or other mechanism on the spending transaction if it proves 
>> insufficient for timely inclusion in a block.
>> +
>> +A node:
>> +  - MAY monitor the blockchain for unspent `to_local_pushme` and 
>> `to_remote_pushme` outputs and try to spend them after 10 confirmations.
>>   ## Rationale
>> @@ -154,7 +167,8 @@ need not consume resources monitoring the channel 
>> state.
>>   There exists a bias towards preferring mutual closes over unilateral 
>> closes,
>>   because outputs of the former are unencumbered by a delay and are 
>> directly
>>   spendable by wallets. In addition, mutual close fees tend to be less 
>> exaggerated
>> -than those of commitment transactions. So, the only reason not to use 
>> the
>> +than those of commitment transactions (or in the case of 
>> `option_simplified_commitment`,
>> +the commitment transaction may require a child transaction to cause 
>> it to be mined). So, the only reason not to use the
>>   signature from `closing_signed` would be if the fee offered was too 
>> small for
>>   it to be processed.
>> diff --git a/09-features.md b/09-features.md
>> index d06fcff..caea38b 100644
>> --- a/09-features.md
>> +++ b/09-features.md
>> @@ -26,6 +26,7 @@ These flags may only be used in the `init` message:
>>   | 3  | `initial_routing_sync` | Indicates that the sending node 
>> needs a complete routing information dump | [BOLT 
>> #7](07-routing-gossip.md#initial-sync) |
>>   | 4/5  | `option_upfront_shutdown_script` | Commits to a shutdown 
>> scriptpubkey when opening channel | [BOLT 
>> #2](02-peer-protocol.md#the-open_channel-message) |
>>   | 6/7  | `gossip_queries`           | More sophisticated gossip 
>> control | [BOLT #7](07-routing-gossip.md#query-messages) |
>> +| 8/9  | `option_simplified_commitment`           | Simplified 
>> commitment transactions | [BOLT #3](03-transactions.md) |
>>   ## Assigned `globalfeatures` flags
>> _______________________________________________
>> Lightning-dev mailing list
>> Lightning-dev at lists.linuxfoundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev
>>
> _______________________________________________
> Lightning-dev mailing list
> Lightning-dev at lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev


More information about the Lightning-dev mailing list