Comments:BIP 0090
Should be harmless and eliminates some technical debt. Recommended. --Luke Dashjr, 2016-12-23
This is actually the opposite of technical debt:
Technical debt (also known as design debt[1] or code debt) is "a concept in programming that reflects the extra development work that arises when code that is easy to implement in the short run is used instead of applying the best overall solution".
The development work was already complete and working in all functional implementations of Bitcoin. This change on the other hand is a regression to simpler-to-code yet clearly imperfect implementation - "used instead of [retaining] the best overall solution". Ironically it also creates more work for core Bitcoin developers at this point.
It would also be incorrect to consider it a material performance optimization (the true target of this fork). While certain implementations may fail to cache the small amount of necessary block version history, that deficiency is not inherent in the consensus rules affected by this proposal. In that sense this is a shortcut in place of, "applying the best overall solution" - in other words, it creates technical debt.
--Eric Voskuil, 2017-01-21
BIP 0090 is a straightforward proposal which objectively simplified Bitcoin Core and improved its performance. The above criticism by Voskuil is almost completely non-responsive to the proposal itself, instead choosing to invite a definition argument about "technical debt".
--Greg Maxwell, 2017-03-14
Maxwell's claim that the criticism is non-responsive to the proposal is incorrect. This proposal is not necessary to achieve the stated performance benefit objective. This is clearly stated above and was explained in detail on bitcoin-dev, and stands unchallenged. A meager amount of cache can achieve the same advantage with little effort or complexity (which has been done). The fact that this proposal "simplified Bitcoin Core" is irrelevant. This is not a Bitcoin Core proposal, it is a Bitcoin proposal. --Eric Voskuil, 2017-03-15
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BIP: 119 Layer: Consensus (soft fork) Title: CHECKTEMPLATEVERIFY Author: Jeremy Rubin j@rubin.io 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`**