Introduction This example demonstrates an RDF model for Bitcoin chain data as well as a Python tool to pull the data from a Bitcoin node into an instance of an AllegroGraph graph database. The model description itself can be found in the Turtle file model. The following Turtle example demonstrates how this RDF model can be used to represent complete chain entities given example is a genesis block — the first block in the mainnet Bitcoin chain; script strings omitted for brevity :. Setup The following examples assume AllegroGraph triple store and assume it is already installed and running on the target machine.
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[bitcoin-dev] BIP: Using Median time-past as endpoint for locktime calculations
In other words, in most Bitcoin smart contracts today, a user can control how a coin can be unlocked by defining restrictions necessary to be satisfied. For instance, one can define a certain amount of time before a transaction can be spent with a timelock , effectively locking that transaction until the specified block height is reached.
In this case, restrictions are being imposed on when funds can be spent, preventing the correct key from unlocking those funds and spending them. However, after that time expires and the block height is reached on the Bitcoin blockchain, the key can unlock those funds and spend them freely.
The when is restricted, but not the what or how. Therefore, covenants have the power to unlock a new set of possibilities to the way Bitcoin can be programmed by enabling a pre-definition of which outputs are acceptable, instead of just controlling the inputs. Although complex covenants with endless possibilities could bring security risks to the network by potentially enabling unexpected or unintended consequences, the proposal for CTV is, for the most part, simple.
In short, CTV allows a Bitcoin user to restrict the way they can spend bitcoin even if they have the key to the bitcoin they want to spend. More importantly, CTV allows these spending restrictions to be enforced non-interactively.
CTV enables these restrictions to be enforced programmatically, without requiring manual interaction by participants, hence increasing the reliability of the covenant. Today, you can spend your UTXOs however you want. Not when they are spent, but how. By bringing these types of new features into Bitcoin, a more diverse set of use cases could be enabled, and a new ecosystem of applications could emerge.
Some of the functionalities that CTV could enable for Bitcoin include enhancements in security, privacy and scalability. With the activation of CTV, users would be able to create more sophisticated custody solutions, like vaults, that could allow a Bitcoin user to pre-define scheduled and limited spending of bitcoin from cold to hot storage, hence limiting the damage from a potential hack.
CTV could also bring payment pools, a type of arrangement where a group of people can share a single UTXO and trustlessly rebalance funds among them, not only increasing their privacy but also enabling better scaling opportunities for Bitcoin. Under the hood, CTV brings a new opcode for Bitcoin, a new addition to the set of operations available in Bitcoin Script. First, naturally, it checks if there is at least one element on the stack.
If there is, it then checks if the element has exactly 32 bytes — the size of a SHA hash. If there is an item on the stack and it has 32 bytes, then CTV will check if it matches the hash of the transaction at the current input index. This step — checking if the element matches the hash — is exactly where the enforcement happens.
This set of transactions would have been previously defined by the user in a contract. Though not necessary for building contracts that can be enforced with CTV, Sapio is a programming language under development designed specifically for this purpose. It abstracts away low-level programming details to facilitate building smart contracts for Bitcoin with, for example, components — reusable pieces of code that improve readability and usability of a program.
Programmers first build a template with Sapio, specifying some conditions, which then outputs a list of partially-signed bitcoin transactions PSBTs that can be leveraged to define an exhaustive set of transactions for spending — allowing us to constrain the set of allowed outputs in a transaction to a set that is smaller than the set of all possible outputs.
Although restrictive, the assumption is that by knowing the TXIDs in advance, the covenant is easier to be enforced as the universe of transactions to be checked is restricted.
The specific hash function being analyzed by the opcode DefaultCheckTemplateVerifyHash hashes parts of a transaction in a serial manner, starting with version and locktime.
Next, the function hashes the scriptSig hash if the transaction is not a SegWit transaction, and then it hashes the number of inputs, the hash of the sequences and the number of outputs. By committing to or determining most of these in advance, not only can the TXID be determined beforehand, but it also enables only a few of those to be set later on to be malleable and makes validation more efficient, as plenty of fields had already been hashed.
The assumption is that a Bitcoin developer programming a covenant is more likely to programmatically change information about the outputs than the inputs, given the fact that a covenant tries to restrict how a coin can be spent. In other words, it enforces the restrictions imposed by the covenant programmed with Sapio.
But that check only happens if the element on the stack is 32 bytes in size. The Bitcoin upgrade process is known for its methodic and careful approach, a vital characteristic to the survival of the network and the ensured correctness of each new addition to the code. Therefore, it is very much unclear whether or not CTV might be added to Bitcoin any time soon. Although not a new proposal — the BIP was created in January — prominent Bitcoin developers argue that there needs to be more extensive testing and discussions around the suggested changes, especially when it relates to possible optimizations and a more detailed consideration of alternatives.
CTV, at the time of writing, would add a limited set of new possibilities to Bitcoin as it seeks to implement a low-risk form of covenants into the protocol. If this is true, and the community needs more time to explore this, then we would actually want APO and CTV and general-purpose covenants. At the moment, readiness for activation is a delicate topic in the Bitcoin community.
In fact, part of the pushback against CTV by some developers is based on a supposed sense of urgency being portrayed by CTV proponents. Reviewer and developer time are Bitcoin's rarest resource, so we want to be respectful of that, despite having some [proof of concept] implementations of eltoo for example. Decker has also shared his thoughts on the intersection between CTV and his proposal. Rubin, on the other hand, told Bitcoin Magazine that he believes it is more useful to ship CTV as is, even though it brings limited functionality, and to iterate on additional features later.
All in all, it might be some time before the two cohorts reach an agreement, but as the proposal gathers more understanding and interest among community members, the path for a consensus to be reached is being paved.
Special thanks to Rubin, who patiently helped the author bridge some gaps in his understanding. For a more detailed explanation of BIP technicals, watch this workshop from a couple of years ago part one and part two. A transcript is available on this link.
Other helpful resources are this conversation , this podcast episode and this other one , as well as a conversation between Rubin and Poelstra. To be a part of the conversation around BIP and hear the latest discussions on the matter, join the bitcoin-dev mailing list. Press Releases. Why Covenants? What Is CTV? By Aaron van Wirdum. By Ben Kaufman. By Nick Abouzeid. By Namcios. By Bitcoin Magazine. By Omar Faridi and Aaron van Wirdum. By Shawn Amick.
By Bitcoin Optech. By Pete Rizzo and Aaron van Wirdum. See More.
nLockTime - Bitcoin Wiki
BlockSci provides a number of different heuristics for determining potential change outputs for a given transaction. The heuristics are sometimes contradictory and thus we provide users with the ability to choose which heuristics they wish to apply. Further, you can combine different change address heuristics through the various composition operators of the blocksci. ChangeHeuristic class. Note that many heuristics can return multiple outputs as candidates. We recommend against simply using one of these heuristics without further refinement for clustering. If input addresses appear as an output address, the client might have reused addresses for change.
Script with CHECKLOCKTIMEVERIFY - Legacy P2SH
You can use locktime to make sure that a transaction is locked until a specific block height , or a point in time. If you do not want your transaction to be locked until a specific block or time, set the locktime field to 0x or anything below the current block height or unix time. Nodes validate every transaction and block they receive. So if they receive a transaction or a block containing a transaction with a locktime in the future, they will reject it. Most transactions do not make use of locktime, so their locktime is set to 0x In order for the locktime to be effective, you need to set one of the sequence values for one of the inputs in the transaction data to anything below the default maximum 0xffffffff. Unix Time is the number of seconds since 1st January As mentioned, the locktime has a dual-purpose for setting either a block height or time.
What is Locktime?
Timelocks have been a long-standing fascination of mine, my first blog post even describing the usage of the checklocktimeverify opcode. Though I knew at the time what the rough role of checklocktimeverify was, I did not know how the different fields in a bitcoin transaction actually play together to enforce timelocks. This is my attempt of disentangling them. Lets start with the 4 byte nLockTime field in a bitcoin transaction.
Bitcoin transaction timelocks
I have written I brief explanation of it here. You can run it as any Python script by having Electrum installed from source. It is coded to testnet if that is any consolation. The script is designed to recreate TXN a Apparently CoinBin and bitcoinlib haven't followed Core when they made this change in 0.
Create a copy of your bitcoin wallet file
Part of the original Bitcoin implementation, nLockTime is a field that specifies the earliest time a transaction may be added to a valid block. A later Bitcoin soft fork allowed nLockTime to alternatively specify the lowest block height a transaction may be added to a valid block. Although every transaction contains the nLockTime field, every wallet up until recently set nLockTime to 0, meaning the transaction was valid in any block. Starting with Bitcoin Core 0. Since a transaction may only be included in a valid block if its nLockTime is in the past, this ensures the CLTV-based timelock has expired before the transaction may be included in a valid block. This allowed an input to specify the earliest time it can be added to a block based on how long ago the output being spent by that input was included in a block on the block chain.
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If the locked funds are not redeemed by a certain amount of time, then the cross-chain transaction changes to a state of Revoked within the smart contracts. Once it changes to Revoked , the funds can no longer be redeemed by the receiver, but instead must be revoked by the sender. The amount of time before the cross-chain transaction expires is defined by the cross-chain smart contracts. For Bitcoin it is 72 hours on mainnet and 8 hours on testnet, while for Ethereum it is 8 hours on mainnet and 4 hours on testnet. Unlike with inbound Ethereum transactions, inbound Bitcoin transactions are revoked not by calling a smart contract, but instead by just spending the bitcoin and sending them to an address that you fully own.
On core wallet it gives an option to choose confirmation time target for your transaction. Whereas on electrum you can specify the block time and date. On most transactions you do not need to make use of this locktime feature. If you want your transaction to be final then simply leave this field to default setting. Depending on the mempool traffic and your fees the transaction will get confirmed in the next few blocks.
Clone the Github repository. Alternatively you can enter the commands step-by-step by cd into. We will set the timelock 6 hours in the past. We need to set the transaction-level locktime in our redeem transaction in order to spend a CLTV.