Comments:BIP 0060
The change at version >= 106 and the later addition of the relay field both created a compatibility break with previous protocol versions. The standard should not assume that old versions of the protocol will not continue to operate indefinitely. This problem should be avoided in any future changes.
Because this message begins the handshake it must be valid for both peers of any version. Because the message does not provide a mechanism for nodes to determine the proper length of the message, older protocol nodes can:
- Fail the handshake for any version message that is not valid according to its understanding.
- Allow a message of any length, ignoring trailing bytes.
- Have clairvoyance about future changes.
The first option will result in the old node being isolated from the network as other peers upgrade. The second option opens a DOS vector (and would have been inconsistent with the protocol). The third option is not possible. At this point older nodes that were properly implemented are broken, since the changes were not backward compatible. Patching such older nodes in order to make them compatible is the only option. In other words, this sort of incompatible change forces an upgrade on existing nodes, which should be avoided. Additionally, properly implemented nodes in the future may prevent such a change from gaining any traction on the network (due to dropped connections under the first option above).
New (or patched) clients operating below either of the protocol breaks described above must be hacked to allow the largest possible valid version message (at the current time) despite not having knowledge of what that is (which is what makes it a hack).
--Eric Voskuil, 2017-02-11
The above issue is complicated by the fact that the original satoshi client change was inconsistently implemented. Protocol version 70001 reads, but does not write, the relay field. Protocol version 70002 reads and writes the relay field. As these clients are still operating on the network, newer clients must accommodate this behavior in order to prevent isolating the older clients.
--Eric Voskuil, 2017-03-26
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BIP: 119 Layer: Consensus (soft fork) Title: CHECKTEMPLATEVERIFY Author: Jeremy Rubin [email protected] Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0119 Status: Draft Type: Standards Track Created: 2020-01-06 License: BSD-3-Clause
==Abstract==
This BIP proposes a new opcode, OP_CHECKTEMPLATEVERIFY, to be activated as a change to the semantics of OP_NOP4.
==Summary==
OP_CHECKTEMPLATEVERIFY uses opcode OP_NOP4 (0xb3) as a soft fork upgrade.
OP_CHECKTEMPLATEVERIFY does the following:
- There is at least one element on the stack, fail otherwise
- The element on the stack is 32 bytes long, NOP otherwise
- The DefaultCheckTemplateVerifyHash of the transaction at the current input index is equal to the element on the stack, fail otherwise
The DefaultCheckTemplateVerifyHash commits to the serialized version, locktime, scriptSigs hash (if any non-null scriptSigs), number of inputs, sequences hash, number of outputs, outputs hash, and currently executing input index.
The recommended standardness rules additionally:
- Reject non-32 byte as SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS.
==Motivation==
This BIP introduces a transaction template, a simple spending restriction that pattern matches a transaction against a hashed transaction specification. OP_CHECKTEMPLATEVERIFY reduces many of the trust, interactivity, and storage requirements inherent with the use of pre-signing in applications. For more details on applications, please see the references.
==Detailed Specification==
The below code is the main logic for verifying CHECKTEMPLATEVERIFY, described in pythonic pseudocode. The canonical specification for the semantics of OP_CHECKTEMPLATEVERIFY as implemented in C++ in the context of Bitcoin Core can be seen in the reference implementation.
The execution of the opcode is as follows:
# CTV always requires at least one stack argument
if len(self.stack) < 1:
return self.errors_with(errors.script_err_invalid_stack_operation)
# CTV only verifies the hash against a 32 byte argument
if len(self.stack[-1]) == 32:
# Ensure the precomputed data required for anti-DoS is available,
# or cache it on first use
if self.context.precomputed_ctv_data == None:
self.context.precomputed_ctv_data = self.context.tx.get_default_check_template_precomputed_data()
# If the hashes do not match, return error
if stack[-1] != self.context.tx.get_default_check_template_hash(self.context.nIn, self.context.precomputed_ctv_data):
return self.errors_with(errors.script_err_template_mismatch)
return self.return_as_nop()
# future upgrade can add semantics for this opcode with different length args
# so discourage use when applicable
if self.flags.script_verify_discourage_upgradable_nops:
return self.errors_with(errors.script_err_discourage_upgradable_nops)
else:
return self.return_as_nop()
The computation of this hash can be implemented as specified below (where self is the transaction type). Care must be taken that in any validation context, the precomputed data must be initialized to prevent Denial-of-Service attacks. Any implementation must cache these parts of the hash computation to avoid quadratic hashing DoS. All variable length computations must be precomputed including hashes of the scriptsigs, sequences, and outputs. See the section "Denial of Service and Validation Costs" below. This is not a performance optimization.
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 s`**