30
votes
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What is the script assembly and execution in P2TR spend (spend from Taproot)
Before we start
I realize your question is only about single-sig scenarios, and you want an answer focused on how validation works. I will address these things, but I think I need to elaborate a bit ...
- 108k
17
votes
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Is sha-1 used in Bitcoin?
SHA1 was never commonly used in Bitcoin, but it there is at least one notable use of it, a P2SH script created by Peter Todd to allow anyone to pay to an address that could be spent by anyone proving ...
- 12.1k
15
votes
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Why is OP_SUBSTR disabled? (and OP_LEFT, OP_RIGHT)
I'm afraid that my answer here can't be better than "Ask Satoshi".
There was a series of bugs found in Bitcoin's early life, and the response by its creator was to disable a number of scripting ...
- 108k
15
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What is Bitcoin locking and unlocking script?
There are quite a lot of things going on there, so let's break it down bit by bit.
Transaction structure
A transaction can be seen as a collection of inputs and outputs. Inputs refer to previously ...
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15
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What does Bitcoin policy language offer the developer that Miniscript doesn't? What is the difference between Bitcoin policy language and Miniscript?
Both answers by James C. and sanket1729 are very good, but I wanted to give a very high-level answer:
Miniscript is an intermediate more structured representation for actual Bitcoin Scripts. It is ...
- 108k
15
votes
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Full list of "special cases" during Bitcoin Script execution (p2sh, p2wsh, etc.)?
As of September 2023, "high-level" script validation with all active consensus rules on the network is approximately this:
Top level evaluation
Execute the scriptSig, and call the resulting ...
- 108k
14
votes
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What are the downsides to enabling potentially suboptimal or unused opcodes in a future soft fork?
Every piece of additional consensus logic has implementation and ongoing maintenance cost which is perpetual and can never be removed without potentially confiscating some user's assets.
When Satoshi ...
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13
votes
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Bitcoin and Smart Contracts
Bitcoin has a scripting language built into it, which allows the creation of many kinds of smart contracts. Examples are atomic swaps, Lightning payment channels and zero-knowledge contingent payments ...
- 1,210
13
votes
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How are sigops calculated?
Each OP_CHECKSIG and OP_CHECKSIGVERIFY is counted as 1 sigop.
Each OP_CHECKMULTISIG or OP_CHECKMULTISIGVERIFY, is counted as 20 sigops if they are found in an output or scriptSig and not part of a ...
- 71.5k
12
votes
What is relation between scriptSig and scriptPubKey?
I had the same question as well and spent forever trying to understand it and finally cracked it.
"The sender (A) only has the Bitcoin Address of the recipient (B), so how does he get the pubKeyHash ...
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12
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What does Bitcoin policy language offer the developer that Miniscript doesn't? What is the difference between Bitcoin policy language and Miniscript?
At a high level:
The policy is compiled to Miniscript.
Miniscript is encoded to Bitcoin Script. (One to One Mapping)
Bitcoin Script is decoded back to Miniscript. (One to One Mapping)
Policy and ...
- 1,412
12
votes
Is it correct to say that Bitcoin has a virtual machine in the same way as Ethereum does?
"Virtual machine" in this context is really just a fancy word for bytecode interpreter. Bitcoin's script language is certainly far simpler than Ethereum's EVM, and its functionalities are in ...
- 108k
12
votes
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How does OP_RETURN burn coins?
What does exactly cause the output containing OP_RETURN to be unspendable?
Simply the fact that no input can possibly unlock coins which are encumbered with such an OP_RETURN-containing script. ...
- 108k
11
votes
Online Bitcoin Script simulator or debugger?
Highly recommend btcdeb by kallewoof. Among other things, you can step through scripts including verify signatures. It is written in c++ and compiles using autotools.
btcdeb
Bitcoin Script debugging ...
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11
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What does Bitcoin policy language offer the developer that Miniscript doesn't? What is the difference between Bitcoin policy language and Miniscript?
Miniscript doesn't compile down to script. It encodes a subset of all Bitcoin script. It is a (very crafty) template language which reduces the Bitcoin script language to specific script expressions ...
- 2,521
11
votes
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Redeem script. script hash, witness script and witness program
The scriptPubKey is the script as it is placed in the transaction output.
The redeemScript (P2SH only) is the script pushed as the last scriptSig item. In P2SH scripts, the scriptPubKey is equal to ...
- 108k
10
votes
nLockTime in Bitcoin Core
I believe you are correct, both about the fact that height-based logic came first and time was added later, and the fact that this is a hard-forking change. A transaction with a locktime > 500000000 ...
- 108k
9
votes
Accepted
How to get address from scriptSig?
The scriptSig needed for spending a P2PKH output (that is, an output of a standard address starting with '1...') consists of two parts, namely the signature and the public key. Looking at your example ...
- 106
9
votes
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How is a "standard" Bitcoin transaction defined?
This is easier said than done, IMO. There are plenty of little fact sheet web pages (e.g. https://www.cryptocompare.com/coins/guides/what-are-the-bitcoin-transaction-types/) lying around that give a ...
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9
votes
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How to tell which part of the previous tx I need to make the hash to sign for an old given tx?
Disclaimer: I am going to assume that you are not completely clueless and that you know what an array is, how to count from 0, and how to match brackets, quotes, and colons so that you can read JSON ...
- 71.5k
9
votes
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Will BTC script be Turing complete in future?
Turing completeness includes the capability to run programs that might not terminate or that might terminate after a very long time. This would cause the blockchain to stall, hence it is a must to ...
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9
votes
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Can Schnorr aggregate signatures be nested inside other Schnorr aggregate signatures?
TL;DR: depending on what you mean, there is probably no published scheme with a security proof, but there is hope for such a scheme.
First, a few clarifications
Aggregation is just a concept, not an ...
- 108k
9
votes
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Is bitcoin script necessary?
was it necessary to have another language for these operations? isn't it possible to write the whole runtime in one language?
To be clear: the goal of the scripting language isn't for defining the ...
- 108k
8
votes
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What's the use of not relaying non-standard transactions if anyone can still use them using P2SH?
As you say, there are two separate concerns here:
There are some scripts that might cause harm to the network.
There are some scripts that might make future upgrades harder.
For the case of harm to ...
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8
votes
Non-standard transaction scripts broadcasting
Standard output scripts are defined by IsStandard() (which calls Solver() to perform the actual script matching). The standard output scripts are as follows:
P2PKH
P2PK
P2SH
P2WPKH
P2WSH
A script ...
- 71.5k
8
votes
Accepted
nLockTime in Bitcoin Core
The Wiki was incorrect (I wrote the original text and I apologize). As indicated in the question, the ordering on the Wiki was backwards. However, upon investigating, I don't believe it was a hard ...
- 12.1k
8
votes
Accepted
What are the scriptPubKey, scriptSig, redeem script and witness for the various output types?
This was answered during the Bitcoin Core PR review club on July 7th 2021 hosted by Gloria Zhao (who also provided this table).
The <public key> in the P2TR (key path) and P2TR (script path) ...
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8
votes
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Why are OP_MUL and OP_DIV disabled in Bitcoin?
OP_MUL and OP_DIV were removed by Satoshi Nakamoto in commit 4bd188c4383d6e614e18f79dc337fbabe8464c82. As with most changes in early days of the development, little rationale was explicitly given by ...
- 8,911
7
votes
Accepted
Why does script need to be purged from transactions for mimblewimble to work?
Scripts are used in Bitcoin to prove authorization to spend the inputs in a transaction. Mimblewimble uses a quirk of CT such that only the owner of a set of inputs can create the transaction in the ...
- 1,210
7
votes
Why does script need to be purged from transactions for mimblewimble to work?
The incompatibility comes down to 2 main factors:
Pruning: an important addition of the mimblewimble proposal is the ability to merge transactions across blocks. If transactions include scripts, ...
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Only top scored, non community-wiki answers of a minimum length are eligible