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#include <bitcoin/script.h>
#include <bitcoin/tx.h>
#include <ccan/endian/endian.h>
#include <common/initial_commit_tx.h>
#include <common/keyset.h>
#include <common/permute_tx.h>
#include <common/status.h>
#include <common/utils.h>
#include <inttypes.h>
/* BOLT #3:
*
* The 48-bit commitment transaction number is obscured by `XOR` with
* the lower 48 bits of:
*
* SHA256(payment_basepoint from open_channel || payment_basepoint from accept_channel)
*/
u64 commit_number_obscurer(const struct pubkey *opener_payment_basepoint,
const struct pubkey *accepter_payment_basepoint)
{
u8 ders[PUBKEY_DER_LEN * 2];
struct sha256 sha;
be64 obscurer = 0;
pubkey_to_der(ders, opener_payment_basepoint);
pubkey_to_der(ders + PUBKEY_DER_LEN, accepter_payment_basepoint);
sha256(&sha, ders, sizeof(ders));
/* Lower 48 bits */
memcpy((u8 *)&obscurer + 2, sha.u.u8 + sizeof(sha.u.u8) - 6, 6);
return be64_to_cpu(obscurer);
}
bool try_subtract_fee(enum side funder, enum side side,
u64 base_fee_msat, u64 *self_msat, u64 *other_msat)
{
u64 *funder_msat;
if (funder == side)
funder_msat = self_msat;
else
funder_msat = other_msat;
if (*funder_msat >= base_fee_msat) {
*funder_msat -= base_fee_msat;
return true;
} else {
*funder_msat = 0;
return false;
}
}
u8 *to_self_wscript(const tal_t *ctx,
u16 to_self_delay,
const struct keyset *keyset)
{
return bitcoin_wscript_to_local(ctx, to_self_delay,
&keyset->self_revocation_key,
&keyset->self_delayed_payment_key);
}
struct bitcoin_tx *initial_commit_tx(const tal_t *ctx,
const struct bitcoin_txid *funding_txid,
unsigned int funding_txout,
u64 funding_satoshis,
enum side funder,
u16 to_self_delay,
const struct keyset *keyset,
u32 feerate_per_kw,
u64 dust_limit_satoshis,
u64 self_pay_msat,
u64 other_pay_msat,
u64 self_reserve_msat,
u64 obscured_commitment_number,
enum side side)
{
u64 base_fee_msat;
struct bitcoin_tx *tx;
size_t n, untrimmed;
assert(self_pay_msat + other_pay_msat <= funding_satoshis * 1000);
/* BOLT #3:
*
* 1. Calculate which committed HTLCs need to be trimmed (see
* [Trimmed Outputs](#trimmed-outputs)).
*/
untrimmed = 0;
/* BOLT #3:
*
* 2. Calculate the base [commitment transaction
* fee](#fee-calculation).
*/
base_fee_msat = commit_tx_base_fee(feerate_per_kw, untrimmed) * 1000;
/* BOLT #3:
*
* 3. Subtract this base fee from the funder (either `to_local` or
* `to_remote`), with a floor of zero (see [Fee Payment](#fee-payment)).
*/
if (!try_subtract_fee(funder, side, base_fee_msat,
&self_pay_msat, &other_pay_msat)) {
/* BOLT #2:
*
* The receiving node MUST fail the channel if:
*...
* - the funder's amount for the initial commitment
* transaction is not sufficient for full [fee
* payment](03-transactions.md#fee-payment).
*/
status_unusual("Funder cannot afford fee"
" on initial commitment transaction");
return NULL;
}
/* BOLT #2:
*
* The receiving node MUST fail the channel if:
*...
* - both `to_local` and `to_remote` amounts for the initial
* commitment transaction are less than or equal to
* `channel_reserve_satoshis`.
*/
if (self_pay_msat <= self_reserve_msat
&& other_pay_msat <= self_reserve_msat) {
status_unusual("Neither self amount %"PRIu64
" nor other amount %"PRIu64
" exceed reserve %"PRIu64
" on initial commitment transaction",
self_pay_msat / 1000,
other_pay_msat / 1000,
self_reserve_msat / 1000);
return NULL;
}
/* Worst-case sizing: both to-local and to-remote outputs. */
tx = bitcoin_tx(ctx, 1, untrimmed + 2);
/* This could be done in a single loop, but we follow the BOLT
* literally to make comments in test vectors clearer. */
n = 0;
/* BOLT #3:
*
* 3. For every offered HTLC, if it is not trimmed, add an
* [offered HTLC output](#offered-htlc-outputs).
*/
/* BOLT #3:
*
* 4. For every received HTLC, if it is not trimmed, add an
* [received HTLC output](#received-htlc-outputs).
*/
/* BOLT #3:
*
* 5. If the `to_local` amount is greater or equal to
* `dust_limit_satoshis`, add a [`to_local`
* Output](#to-local-output).
*/
if (self_pay_msat / 1000 >= dust_limit_satoshis) {
u8 *wscript = to_self_wscript(tmpctx, to_self_delay,keyset);
tx->output[n].amount = self_pay_msat / 1000;
tx->output[n].script = scriptpubkey_p2wsh(tx, wscript);
n++;
}
/* BOLT #3:
*
* 6. If the `to_remote` amount is greater or equal to
* `dust_limit_satoshis`, add a [`to_remote`
* Output](#to-remote-output).
*/
if (other_pay_msat / 1000 >= dust_limit_satoshis) {
/* BOLT #3:
*
* #### `to_remote` Output
*
* This output sends funds to the other peer, thus is a simple
* P2WPKH to `remotekey`.
*/
tx->output[n].amount = other_pay_msat / 1000;
tx->output[n].script = scriptpubkey_p2wpkh(tx,
&keyset->other_payment_key);
n++;
}
assert(n <= tal_count(tx->output));
tal_resize(&tx->output, n);
/* BOLT #3:
*
* 7. Sort the outputs into [BIP 69
* order](#transaction-input-and-output-ordering)
*/
permute_outputs(tx->output, tal_count(tx->output), NULL);
/* BOLT #3:
*
* ## Commitment Transaction
*
* * version: 2
*/
assert(tx->version == 2);
/* BOLT #3:
*
* * locktime: upper 8 bits are 0x20, lower 24 bits are the lower
* 24 bits of the obscured commitment transaction number.
*/
tx->lock_time
= (0x20000000 | (obscured_commitment_number & 0xFFFFFF));
/* BOLT #3:
*
* * txin count: 1
* * `txin[0]` outpoint: `txid` and `output_index` from
* `funding_created` message
*/
tx->input[0].txid = *funding_txid;
tx->input[0].index = funding_txout;
/* BOLT #3:
*
* * `txin[0]` sequence: upper 8 bits are 0x80, lower 24 bits are
* upper 24 bits of the obscured commitment transaction number.
*/
tx->input[0].sequence_number
= (0x80000000 | ((obscured_commitment_number>>24) & 0xFFFFFF));
/* Input amount needed for signature code. */
tx->input[0].amount = tal_dup(tx->input, u64, &funding_satoshis);
return tx;
}