Create bitcoin transaction
That UTXO contains a locking script defining the conditions required to spend it. The validation software will then take the unlocking script contained in the input that is attempting to spend this UTXO and execute the two scripts. In the original bitcoin client, the unlocking and locking scripts were concatenated and executed in sequence. For security reasons, this was changed in , because of a vulnerability that allowed a malformed unlocking script to push data onto the stack and corrupt the locking script.
In the current implementation, the scripts are executed separately with the stack transferred between the two executions, as described next. First, the unlocking script is executed, using the stack execution engine.
If the unlocking script executed without errors e. Note that the UTXO is permanently recorded in the blockchain, and therefore is invariable and is unaffected by failed attempts to spend it by reference in a new transaction. Figure is an example of the unlocking and locking scripts for the most common type of bitcoin transaction a payment to a public key hash , showing the combined script resulting from the concatenation of the unlocking and locking scripts prior to script validation.
Figure Combining scriptSig and scriptPubKey to evaluate a transaction script Scripting Language The bitcoin transaction script language, called Script, is a Forth-like reverse-polish notation stack-based execution language. Script is a very simple language that was designed to be limited in scope and executable on a range of hardware, perhaps as simple as an embedded device, such as a handheld calculator. It requires minimal processing and cannot do many of the fancy things modern programming languages can do.
In the case of programmable money, that is a deliberate security feature. A stack is a very simple data structure, which can be visualized as a stack of cards. A stack allows two operations: push and pop. Push adds an item on top of the stack. Pop removes the top item from the stack. The scripting language executes the script by processing each item from left to right.
Numbers data constants are pushed onto the stack. Operators push or pop one or more parameters from the stack, act on them, and might push a result onto the stack. Bitcoin transaction scripts usually contain a conditional operator, so that they can produce the TRUE result that signifies a valid transaction.
When the script execution ends, you should be left with the value TRUE on the stack. Although most locking scripts refer to a bitcoin address or public key, thereby requiring proof of ownership to spend the funds, the script does not have to be that complex. Any combination of locking and unlocking scripts that results in a TRUE value is valid. The simple arithmetic we used as an example of the scripting language is also a valid locking script that can be used to lock a transaction output.
Not only is this a valid transaction output locking script, but the resulting UTXO could be spent by anyone with the arithmetic skills to know that the number 2 satisfies the script. See Appendix A for details. Turing Incompleteness The bitcoin transaction script language contains many operators, but is deliberately limited in one important way—there are no loops or complex flow control capabilities other than conditional flow control.
This ensures that the language is not Turing Complete, meaning that scripts have limited complexity and predictable execution times. Script is not a general-purpose language. Remember, every transaction is validated by every full node on the bitcoin network. A limited language prevents the transaction validation mechanism from being used as a vulnerability. Stateless Verification The bitcoin transaction script language is stateless, in that there is no state prior to execution of the script, or state saved after execution of the script.
Therefore, all the information needed to execute a script is contained within the script. A script will predictably execute the same way on any system. If your system verifies a script, you can be sure that every other system in the bitcoin network will also verify the script, meaning that a valid transaction is valid for everyone and everyone knows this.
This predictability of outcomes is an essential benefit of the bitcoin system. These limitations are temporary and might be lifted by the time you read this. Until then, the five standard types of transaction scripts are the only ones that will be accepted by the reference client and most miners who run the reference client.
Although it is possible to create a nonstandard transaction containing a script that is not one of the standard types, you must find a miner who does not follow these limitations to mine that transaction into a block. Check the source code of the Bitcoin Core client the reference implementation to see what is currently allowed as a valid transaction script.
These contain a locking script that encumbers the output with a public key hash, more commonly known as a bitcoin address. Transactions that pay a bitcoin address contain P2PKH scripts. An output locked by a P2PKH script can be unlocked spent by presenting a public key and a digital signature created by the corresponding private key.
Alice made a payment of 0. Figures and show in two parts a step-by-step execution of the combined script, which will prove this is a valid transaction. With this script form, the public key itself is stored in the locking script, rather than a public-key-hash as with P2PKH earlier, which is much shorter. Pay-to-public-key-hash was invented by Satoshi to make bitcoin addresses shorter, for ease of use.
Pay-to-public-key is now most often seen in coinbase transactions, generated by older mining software that has not been updated to use P2PKH. Evaluating a script for a P2PKH transaction Part 2 of 2 Multi-Signature Multi-signature scripts set a condition where N public keys are recorded in the script and at least M of those must provide signatures to release the encumbrance.
This is also known as an M-of-N scheme, where N is the total number of keys and M is the threshold of signatures required for validation. For example, a 2-of-3 multi-signature is one where three public keys are listed as potential signers and at least two of those must be used to create signatures for a valid transaction to spend the funds. At this time, standard multi-signature scripts are limited to at most 15 listed public keys, meaning you can do anything from a 1-of-1 to a of multi-signature or any combination within that range.
The limitation to 15 listed keys might be lifted by the time this book is published, so check the isStandard function to see what is currently accepted by the network. In this case, the condition is whether the unlocking script has a valid signature from the two private keys that correspond to two of the three public keys set as an encumbrance.
Many developers have tried to use the transaction scripting language to take advantage of the security and resilience of the system for applications such as digital notary services, stock certificates, and smart contracts.
Many developers consider such use abusive and want to discourage it. Others view it as a demonstration of the powerful capabilities of blockchain technology and want to encourage such experimentation. Moreover, such transactions create UTXO that cannot be spent, using the destination bitcoin address as a free-form byte field. Many applications put a prefix in front of the data to help identify the application.
Two new command-line options have been added in Bitcoin Core as of version 0. In February , in version 0. Pay-to-Script-Hash P2SH Pay-to-script-hash P2SH was introduced in as a powerful new type of transaction that greatly simplifies the use of complex transaction scripts. In Chapter 1 we introduced Mohammed, an electronics importer based in Dubai. With the multi-signature scheme, any payments made by customers are locked in such a way that they require at least two signatures to release, from Mohammed and one of his partners or from his attorney who has a backup key.
A multi-signature scheme like that offers corporate governance controls and protects against theft, embezzlement, or loss. Given the preceding script, Mohammed would have to communicate this script to every customer prior to payment. Because you automatically expend all of the amount in the UTXOs that you use, it's critically important to make sure that you know: 1 precisely what UTXOs you're using; 2 exactly how much money they contain; 3 exactly how much money you're sending out; and 4 what the difference is.
If you mess up and you use the wrong UTXO with more money than you thought or if you send out too little money, the excess is lost. Don't make that mistake! Know your inputs and outputs precisely. Or better, don't use raw transactions except as part of a carefully considered and triple-checked program. Bitcoin Fees has a nice live assessment. Currently Bitcoin Fees suggests a transaction fee of about 10, satoshis, which is the same as.
Yes, that's for the mainnet, not the testnet, but we want to test out things realistically, so that's what we're going to use. In this case, that means taking the. But that's always why we have Lightning. The Bitcoin Fees site lists expected times, from an expected 0 blocks, to Since blocks are built on average every 10 minutes, that's the difference between a few minutes and a few hours!
So, choose a transaction fee that's appropriate for what you're sending. Note that you should never drop below the minimum relay fee, which is. Write the Raw Transaction You're now ready to create the raw transaction. This uses the createrawtransaction command, which might look a little intimidating. Protect normal words like "this", but you don't need to protect normal numbers: 0. You'll get used to it. Are you spending the right transaction? Does it contain the expected amount of money?
Check with bitcoin-cli gettransaction and be sure to look at the right vout. Check your vout. Are you sending the right amount? Is it going to the right address? Finally, do the math to make sure the money balances.
Does the value of the UTXO minus the amount being spent equal the expected transaction fee? This is the last frontier of Bitcoin transactions, because it's a standard field in transactions that was originally intended for a specific purpose, but was never fully implemented. So now there's this integer sitting around in transactions that could be repurposed for other uses.
And, in fact, it has been. As of this writing there are three different uses for the variable that's called nSequence in the Bitcoin Core code: it enables RBF, nLockTime, and relative timelocks. If there's nothing weird going on, nSequence will be set to Setting it to a lower value signals that special stuff is going on. Sign the Raw Transaction To date, your raw transaction is just something theoretical: you could send it, but nothing has been promised. You have to do a few things to get it out onto the network.
A software package called "JQ" could do better, as we'll explain in an upcoming interlude. Send the Raw Transaction You've now got a ready-to-go raw transaction, but it doesn't count until you actually put it on the network, which you do with the sendrawtransaction command. Not only does it show the amount sent, but it also shows the transaction fee. And, it's already received a confirmation, because we offered a fee that would get it swept up into a block quickly.
You're now a few satoshis poorer! When you create a raw transaction to send that money back out, you use one or more UTXOs to fund it. You then can create a raw transaction, sign it, and send it on the Bitcoin network.
BISNIS FOREX TERMUDAH
We need a list of unspent UTXOs in our wallet to create the input part of our transaction. Then you select the ones you want to spend. To determine an UTXO you will need its txid and vout. You will also need the scriptPubKey when signing the transaction. Total amount spent needs to be lower than the sum of all amount of UTXOs we are using.
Create the Raw Transaction First we need the destination address where we are going to send the funds to. In this example we are going to use only one destination address. We set feerate to 0. We could also check the transaction in a block explorer:. Please consider supporting us by disabling your ad blocker. Create And Sign Bitcoin Transactions With Golang March 21, Blockchain Development About a month ago I had written about creating and importing private keys as well as generating public addresses for Bitcoin and several other cryptocurrencies using the Go programming language.
This previous tutorial had more of an emphasis on creating cryptocurrency wallets with Golang than anything. The next step in making Bitcoin and other cryptocurrencies useful is to be able to transfer or send them to other people. Sending Bitcoin is part of a process known as creating and broadcasting a transaction. Going forward, it must be made clear that I am not a cryptocurrency or cryptography expert. Understanding the Moving Pieces of Bitcoin Transactions Before we get into the coding, we need to understand how transactions work.
It is an unnecessarily difficult concept that too me quite a while to figure out using Golang. It is much easier with other technologies like Node. If you want an explanation of concepts, far deeper than mine, check out Bitcoins the Hard Way: Using the Raw Bitcoin Protocol , which is where I got the fundamentals necessary to accomplish the task in Go.
The private key is used for two things. When we have an unsigned transaction, the private key will be used to sign the transaction proving that the funds can be spent. The UTXO has information such as the transaction hash id, the public key script, and the amount of satoshi in the transaction.
We can figure out the public key script through a public address. A public key script will be created and added to a redeeming transaction rather than the source UTXO transaction. Finally, the amount in satoshis must be determined. This amount must exist in the UTXO.
Building and Signing a Transaction with Go There will be quite a bit happening in our Go application to make transactions possible. Before we add code, we need to get our package dependencies. From the command line, execute the following: go get github. However, the signed transaction data can be broadcasted just once. In the CreateTransaction function a few things are going to happen. DecodeWIF secret if err! NewAddressPubKey wif.
NewMsgTx wire. DecodeAddress addresspubkey. MainNetParams if err!
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NewMsgTx wire. DecodeAddress addresspubkey. MainNetParams if err! The sourceTxHash variable is our new transaction id for the redeem transaction. NewTxIn prevOut, nil, nil redeemTx. SignatureScript redeemTx, 0, sourceTx. PkScript, txscript. SigHashAll, wif. PrivKey, false if err! NewEngine sourceTx.
PkScript, redeemTx, 0, flags, nil, nil, amount if err! Execute ; err! Buffer var signedTx bytes. Buffer sourceTx. String transaction. EncodeToString unsignedTx. Bytes transaction. EncodeToString signedTx. EncodeAddress transaction. Marshal transaction fmt.
Use testnet values when testing. Conclusion You just saw how to create and sign Bitcoin transactions, offline, with the Go programming language. Like I said earlier, I am not a cryptocurrency expert, nor am I a cryptography expert. Many of the concepts of this tutorial were taken from the Bitcoins the Hard Way: Using the Raw Bitcoin Protocol article which is incredibly helpful.
The btcd and btcutil packages have minimal documentation dispersed across everywhere. A lot of the code in this tutorial is Frankenstein code from various locations in the GoDocs. If you want to learn how to apply this tutorial towards creating a fully functional cryptocurrency hardware wallet, check out the tutorial I wrote titled, Create a Bitcoin Hardware Wallet with Golang and a Raspberry Pi Zero.
Signature scripts are also called scriptSigs. Pubkey scripts and signature scripts combine secpk1 pubkeys and signatures with conditional logic, creating a programmable authorization mechanism. This lets the pubkey script verify that Bob owns the private key which created the public key. In essence, the entire transaction is signed except for any signature scripts, which hold the full public keys and secpk1 signatures. After putting his signature and public key in the signature script, Bob broadcasts the transaction to Bitcoin miners through the peer-to-peer network.
Each peer and miner independently validates the transaction before broadcasting it further or attempting to include it in a new block of transactions. Statelessness ensures that once a transaction is added to the block chain, there is no condition which renders it permanently unspendable. Turing-incompleteness specifically, a lack of loops or gotos makes the script language less flexible and more predictable, greatly simplifying the security model. The figure below shows the evaluation of a standard P2PKH pubkey script; below the figure is a description of the process.
The public key also from the signature script is pushed on top of the signature. If the value is false it immediately terminates evaluation and the transaction validation fails. Otherwise it pops the true value off the stack. If false is not at the top of the stack after the pubkey script has been evaluated, the transaction is valid provided there are no other problems with it.
Receivers do care about the script conditions and, if they want, they can ask spenders to use a particular pubkey script. Unfortunately, custom pubkey scripts are less convenient than short Bitcoin addresses and there was no standard way to communicate them between programs prior to widespread implementation of the now deprecated BIP70 Payment Protocol discussed later.
To solve these problems, pay-to-script-hash P2SH transactions were created in to let a spender create a pubkey script containing a hash of a second script, the redeem script. Bob creates a redeem script with whatever script he wants, hashes the redeem script, and provides the redeem script hash to Alice.
The peer-to-peer network ensures the full redeem script hashes to the same value as the script hash Alice put in her output; it then processes the redeem script exactly as it would if it were the primary pubkey script, letting Bob spend the output if the redeem script does not return false. This is the IsStandard test, and transactions which pass it are called standard transactions. Non-standard transactions—those that fail the test—may be accepted by nodes not using the default Bitcoin Core settings.
If they are included in blocks, they will also avoid the IsStandard test and be processed. Besides making it more difficult for someone to attack Bitcoin for free by broadcasting harmful transactions, the standard transaction test also helps prevent users from creating transactions today that would make adding new transaction features in the future more difficult.
For example, as described above, each transaction includes a version number—if users started arbitrarily changing the version number, it would become useless as a tool for introducing backwards-incompatible features. As of Bitcoin Core 0. The most common use of P2SH is the standard multisig pubkey script, with the second most common use being the Open Assets Protocol.
Another common redeemScript used for P2SH is storing textual data on the blockchain. The first bitcoin transaction ever made included text, and P2SH is a convenient method of storing text on the blockchain as its possible to store up to 1. An example of storing text on the blockchain using P2SH can be found in this repository.
However, after the soft fork is activated, new nodes will perform a further verification for the redeem script. Therefore, to redeem a P2SH transaction, the spender must provide the valid signature or answer in addition to the correct redeem script. In multisig pubkey scripts, called m-of-n, m is the minimum number of signatures which must match a public key; n is the number of public keys being provided.
The signature script must provide signatures in the same order as the corresponding public keys appear in the pubkey script or redeem script. It is preferable to use null data transactions over transactions that bloat the UTXO database because they cannot be automatically pruned; however, it is usually even more preferable to store data outside transactions if possible. Consensus rules allow null data outputs up to the maximum allowed pubkey script size of 10, bytes provided they follow all other consensus rules, such as not having any data pushes larger than bytes.
Bitcoin Core 0. There must still only be a single null data output and it must still pay exactly 0 satoshis. The -datacarriersize Bitcoin Core configuration option allows you to set the maximum number of bytes in null data outputs that you will relay or mine.
When you try to broadcast your transaction to a peer running the default settings, you will receive an error. If you create a redeem script, hash it, and use the hash in a P2SH output, the network sees only the hash, so it will accept the output as valid no matter what the redeem script says. This allows payment to non-standard scripts, and as of Bitcoin Core 0.
Note: standard transactions are designed to protect and help the network , not prevent you from making mistakes. The transaction must be smaller than , bytes. Bare non-P2SH multisig transactions which require more than 3 public keys are currently non-standard. It cannot push new opcodes, with the exception of opcodes which solely push data to the stack. Exception: standard null data outputs must receive zero satoshis. Since the signature protects those parts of the transaction from modification, this lets signers selectively choose to let other people modify their transactions.
The various options for what to sign are called signature hash types. This input, as well as other inputs, are included in the signature. The sequence numbers of other inputs are not included in the signature, and can be updated. Allows anyone to add or remove other inputs. Because each input is signed, a transaction with multiple inputs can have multiple signature hash types signing different parts of the transaction. For example, a single-input transaction signed with NONE could have its output changed by the miner who adds it to the block chain.
Called nLockTime in the Bitcoin Core source code. The locktime indicates the earliest time a transaction can be added to the block chain. Locktime allows signers to create time-locked transactions which will only become valid in the future, giving the signers a chance to change their minds. If any of the signers change their mind, they can create a new non-locktime transaction. The new transaction will use, as one of its inputs, one of the same outputs which was used as an input to the locktime transaction.
This makes the locktime transaction invalid if the new transaction is added to the block chain before the time lock expires. Care must be taken near the expiry time of a time lock. The peer-to-peer network allows block time to be up to two hours ahead of real time, so a locktime transaction can be added to the block chain up to two hours before its time lock officially expires.
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