templateはなにが可変であり、なにが固定なのか、を整理する。
様々な場所に情報があるが、BIPに記されたpython codeを見るのが一番良い。
def ser_compact_size(l): r = b"" if l < 253: # Serialize as unsigned char r = struct.pack("B", l) elif l < 0x10000: # Serialize as unsigned char 253 followed by unsigned 2 byte integer (little endian) r = struct.pack("<BH", 253, l) elif l < 0x100000000: # Serialize as unsigned char 254 followed by unsigned 4 byte integer (little endian) r = struct.pack("<BI", 254, l) else: # Serialize as unsigned char 255 followed by unsigned 8 byte integer (little endian) r = struct.pack("<BQ", 255, l) return r def ser_string(s): return ser_compact_size(len(s)) + s class CTxOut: def serialize(self): r = b"" # serialize as signed 8 byte integer (little endian) r += struct.pack("<q", self.nValue) r += ser_string(self.scriptPubKey) return r def get_default_check_template_precomputed_data(self): result = {} # If there are no scriptSigs we do not need to precompute a hash if any(inp.scriptSig for inp in self.vin): result["scriptSigs"] = sha256(b"".join(ser_string(inp.scriptSig) for inp in self.vin)) # The same value is also pre-computed for and defined in BIP-341 and can be shared. # each nSequence is packed as 4 byte unsigned integer (little endian) result["sequences"] = sha256(b"".join(struct.pack("<I", inp.nSequence) for inp in self.vin)) # The same value is also pre-computed for and defined in BIP-341 and can be shared # See class CTxOut above for details. result["outputs"] = sha256(b"".join(out.serialize() for out in self.vout)) return result parameter precomputed must be passed in for DoS resistance def get_default_check_template_hash(self, nIn, precomputed = None): if precomputed == None: precomputed = self.get_default_check_template_precomputed_data() r = b"" # Serialize as 4 byte signed integer (little endian) r += struct.pack("<i", self.nVersion) # Serialize as 4 byte unsigned integer (little endian) r += struct.pack("<I", self.nLockTime) # we do not include the hash in the case where there is no # scriptSigs if "scriptSigs" in precomputed: r += precomputed["scriptSigs"] # Serialize as 4 byte unsigned integer (little endian) r += struct.pack("<I", len(self.vin)) r += precomputed["sequences"] # Serialize as 4 byte unsigned integer (little endian) r += struct.pack("<I", len(self.vout)) r += precomputed["outputs"] # Serialize as 4 byte unsigned integer (little endian) r += struct.pack("<I", nIn) return sha256(r) OP_CHECKTEMPLATEVERIFY（OP_CTV）は「将来使われるトランザクションの形をあらかじめ決めておき、そこから外れる支払いを無効とする」仕組みを提供する。したがって、意図しない送金や改ざんを防ぎながら、VaultやChannel Factoryのような特定用途の“Covenant”機能をシンプルかつ安全に実装できる。
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