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vaults: make recovery transaction explicit

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Instead of implicitly detecting whether or not an OP_VAULT/OP_UNVAULT
spend is a recovery spend by scanning outputs for matching
scriptPubKeys, explicitly indicate recoveries by requiring a witness
stack element that is either -1 in the case of no recovery OR
corresponds to an output index that is the recovery output.
This commit is contained in:
James O'Beirne 2023-02-15 13:56:22 -05:00
parent 9124f2940e
commit c589490f98
1 changed files with 14 additions and 20 deletions
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@ -279,32 +279,26 @@ where
** If <code><recovery-params></code> is less than 32 bytes, script execution when spending this output MUST fail and terminate immediately. ** If <code><recovery-params></code> is less than 32 bytes, script execution when spending this output MUST fail and terminate immediately.
** Because the recovery scriptPubKey is committed to with a hash, witness version upgradeability is preserved. ** Because the recovery scriptPubKey is committed to with a hash, witness version upgradeability is preserved.
==== Check for recovery ==== ==== Witness stack ====
After the witness program is parsed, it must be determined whether this input After the witness program is parsed, it must be determined whether this input
is being spent towards a recovery. If an output in the spending transaction is is being spent towards a recovery.
found whose scriptPubKey hashes to the recovery sPK hash (the
first component of <code><recovery-params></code>), the interpreter will
evaluate for recovery. Otherwise, the interpreter will evaluate assuming a withdrawal
is being triggered.
In pseudocode: Witness stack shown top to bottom:
<source lang="python"> <source>
is_recovery = False <recovery-vout-idx>
recovery_out: Optional[CTxOut] = None [other potential witness stack items ...]
for out in spending_tx.vout:
if tagged_hash("VaultRecoverySPK", out.scriptPubKey) == recovery_sPK_hash:
is_recovery = True
recovery_out = out
if is_recovery:
eval_for_recovery(recovery_out)
else:
eval_for_withdrawal_trigger()
</source> </source>
where
* <code><recovery-vout-idx></code> is an integer indicating which output, if any, is a recovery output.
** If this value cannot be decoded as a CScriptNum and cast to an integer, script execution MUST fail and terminate immediately.
** If this value is less than -1, script execution MUST fail and terminate immediately.
** If this value is greater than or equal to 0, this spend is a recovery transaction and this value denotes the recovery output that corresponds to this vault input.
* The parse of the other stack items depends on whether or not this is a recovery spend.
==== <code>OP_VAULT</code> evaluation for recovery spend ==== ==== <code>OP_VAULT</code> evaluation for recovery spend ====
* If the recovery output does not have an <code>nValue</code> greater than this input's amount, the script MUST fail and terminate immediately. * If the recovery output does not have an <code>nValue</code> greater than this input's amount, the script MUST fail and terminate immediately.