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Bitcoin uses a scripting system for transactions. Forth -like, Script is simple, stack-based, and processed from left to right. It is intentionally not Turing-complete, with no loops. A script is essentially a list of instructions recorded with each transaction that describe how the next person wanting to spend the Bitcoins being transferred can gain access to them. Bitcoin wiki script aculos script for a typical Bitcoin transfer to destination Bitcoin address D simply encumbers future spending of the bitcoins with two things: Scripting provides the flexibility to change the parameters of what's needed to spend transferred Bitcoins.

For example, the scripting system could be used to require two private keys, or a combination of several keys, or even no keys at all. A transaction is valid if nothing in the combined script triggers failure and the top stack item is True non-zero when the script exits. The party that originally sent the Bitcoins now being spent dictates the script operations that will occur last in order to release them for use in another transaction.

The party wanting to spend them must provide the input s to the previously recorded script that results in the combined script completing execution with a true value on the top of bitcoin wiki script aculos stack. This document is for information purposes only. De facto, Bitcoin script bitcoin wiki script aculos defined by the code run by the network to check the validity of blocks. The stacks hold byte vectors. When used as numbers, byte vectors are interpreted as little-endian variable-length integers with the most significant bit determining the sign of the integer.

Thus 0x81 represents Positive 0 is represented by a null-length vector. Byte vectors are interpreted as Booleans where Bitcoin wiki script aculos is represented by any representation of zero and True is represented by any representation of non-zero. Leading zeros in an integer and negative zero are allowed in blocks but get rejected by the stricter requirements which standard full nodes put on transactions before retransmitting them.

Byte vectors on the stack are not allowed to be more than bytes long. Opcodes which take integers and bools off the stack require that they be no more than 4 bytes long, but addition and subtraction can overflow and result in a 5 byte integer being put on the stack. There are some words which existed in very early versions of Bitcoin but were removed out of concern that the client might have a bug in their implementation. The removed opcodes are sometimes said to be "disabled", but this is something of a misnomer because there is absolutely no way for anyone using Bitcoin to use these opcodes they simply do not exist bitcoin wiki script aculos in the protocoland there are also no solid plans to ever re-enable all of these opcodes.

They are listed here for historical interest only. False is zero or negative zero using any number of bytes or an empty array, and True is anything else. If any input value for any of these commands is longer than 4 bytes, bitcoin wiki script aculos script must abort and fail. If any opcode marked as disabled is present in a script - it must also abort and fail.

These words are used internally for assisting with transaction matching. They are invalid if used in actual scripts. Any opcode not assigned is also reserved. Using an unassigned opcode makes the transaction invalid. The following is a list of interesting scripts. When notating scripts, data to be pushed to the stack is generally enclosed in angle brackets and data push commands are omitted. Non-bracketed words are bitcoin wiki script aculos. Note that there is a small number of standard script forms that are relayed from node to node; non-standard scripts are accepted if they are in a block, but nodes will not relay them.

This was used by early versions of Bitcoin where people paid directly to IP addresses, before Bitcoin addresses were introduced. The disadvantage of this transaction form is that the whole public key needs to be known in advance, implying longer payment addresses, and that it provides less protection in the event of a break in the ECDSA signature algorithm. The standard way to mark a transaction as provably unspendable is with a scriptPubKey of the following form:.

Thus the output can be immediately pruned from the UTXO set even if it has not been spent. With some software changes such transactions can be used as a way to bitcoin wiki script aculos funds to miners in addition to transaction fees: This mechanism may be used in the future bitcoin wiki script aculos fidelity bonds to sacrifice funds in a provable way.

Anyone-Can-Spend outputs are currently considered non-standard, and are not relayed on the Bitcoin wiki script aculos network. Transaction a4bfa8abae5f25dae9d89e4eb67dfacafc1ddc5abbc31b is an interesting puzzle. To spend the transaction you need to come up with some data such that hashing the data twice results in the given hash. This transaction was successfully spent by 09fbe71fd1db51ffda40cc0e4f8c8c2c4ab1.

The required bitcoin wiki script aculos happened to be the Genesis blockand the given hash in the script was the genesis block header hashed twice with SHA Note that while transactions like this are fun, they are not secure, because they do not contain any signatures and thus any transaction attempting to spend them can be replaced with a different transaction sending bitcoin wiki script aculos funds somewhere else.

In Peter Todd created scripts that result in true if a hash collision is found. Bitcoin addresses resulting from these scripts can have money sent to them. If someone finds a hash collision they can spend the bitcoins on that address, so this setup acts as an incentive for somebody to do so.

See the bitcointalk thread [1] and reddit thread [2] for more details. Retrieved from " https: Technical Vocabulary Bitcoin Core documentation.

Navigation menu Personal tools Create account Log in. Views Read View source View history. Sister projects Essays Source.

This page was last edited on 26 Mayat Content is available under Creative Commons Attribution 3. Privacy policy About Bitcoin Wiki Disclaimers. An empty array of bytes is pushed onto the stack. This is not a no-op: The next two bytes contain the number of bytes to be pushed onto the stack in little endian order.

The next four bytes contain the number of bytes to be pushed onto the stack in little endian order. If the top stack value is not False, the statements are executed.

The top stack value is removed. All blocks must end, or the transaction is invalid. Marks transaction as invalid if top stack value is not true. Marks transaction as invalid.

Such outputs are provably unspendable, reducing their cost to the network. Keeps only characters left of the specified point in a string. Keeps only characters right of the specified point in a string. Boolean exclusive or between each bit in the inputs. If it is, 1 is returned, 0 otherwise. Starting with the subsequent public key, it compares the second signature bitcoin wiki script aculos each remaining public key until it finds an ECDSA match.

Bitcoin wiki script aculos process is repeated until all signatures have been checked or not enough public keys remain to produce a successful result. All signatures need to match a public key. Because public keys are not checked again if they fail any signature comparison, signatures must be placed in the scriptSig using the same order as their corresponding public bitcoin wiki script aculos were placed in the scriptPubKey or redeemScript.

If all signatures are valid, 1 is returned, 0 otherwise. Due to a bug, one extra unused value is removed from the stack.

Transaction is also invalid if 1. The precise semantics are described in BIP Marks transaction as invalid if the relative lock time of the input enforced by BIP with bitcoin wiki script aculos is not equal to or longer than the value of the top stack item.

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A transaction is a transfer of Bitcoin value that is broadcast to the network and collected into blocks. A transaction typically references previous transaction outputs as new transaction inputs and dedicates all input Bitcoin values to new outputs. Transactions are not encrypted, so it is possible to browse and view every transaction ever collected into a block. Once transactions are buried under enough confirmations they can be considered irreversible. Standard transaction outputs nominate addresses , and the redemption of any future inputs requires a relevant signature.

All transactions are visible in the block chain , and can be viewed with a hex editor. A block chain browser is a site where every transaction included within the block chain can be viewed in human-readable terms. This is useful for seeing the technical details of transactions in action and for verifying payments. The input in this transaction imports 50 BTC from output 0 in transaction f5d Then the output sends 50 BTC to a Bitcoin address expressed here in hexadecimal When the recipient wants to spend this money, he will reference output 0 of this transaction in an input of his own transaction.

An input is a reference to an output from a previous transaction. Multiple inputs are often listed in a transaction. All of the new transaction's input values that is, the total coin value of the previous outputs referenced by the new transaction's inputs are added up, and the total less any transaction fee is completely used by the outputs of the new transaction. Previous tx is a hash of a previous transaction. Index is the specific output in the referenced transaction.

ScriptSig is the first half of a script discussed in more detail later. The script contains two components, a signature and a public key. The public key must match the hash given in the script of the redeemed output. The public key is used to verify the redeemers signature, which is the second component.

More precisely, the second component is an ECDSA signature over a hash of a simplified version of the transaction. It, combined with the public key, proves the transaction was created by the real owner of the address in question. Various flags define how the transaction is simplified and can be used to create different types of payment. An output contains instructions for sending bitcoins. ScriptPubKey is the second half of a script discussed later. There can be more than one output, and they share the combined value of the inputs.

Because each output from one transaction can only ever be referenced once by an input of a subsequent transaction, the entire combined input value needs to be sent in an output if you don't want to lose it.

Any input bitcoins not redeemed in an output is considered a transaction fee ; whoever generates the block will get it. To verify that inputs are authorized to collect the values of referenced outputs, Bitcoin uses a custom Forth-like scripting system. The input's scriptSig and the referenced output's scriptPubKey are evaluated in that order , with scriptPubKey using the values left on the stack by scriptSig. The input is authorized if scriptPubKey returns true.

Through the scripting system, the sender can create very complex conditions that people have to meet in order to claim the output's value. For example, it's possible to create an output that can be claimed by anyone without any authorization.

It's also possible to require that an input be signed by ten different keys, or be redeemable with a password instead of a key. It is possible to design more complex types of transactions, and link them together into cryptographically enforced agreements. These are known as Contracts. A Bitcoin address is only a hash, so the sender can't provide a full public key in scriptPubKey.

When redeeming coins that have been sent to a Bitcoin address, the recipient provides both the signature and the public key. The script verifies that the provided public key does hash to the hash in scriptPubKey, and then it also checks the signature against the public key. P2SH addresses were created with the motivation of moving "the responsibility for supplying the conditions to redeem a transaction from the sender of the funds to the redeemer.

They allow the sender to fund an arbitrary transaction, no matter how complicated, using a byte hash" 1. Pay-to-Pubkey-hash addresses are similarly a byte hash of the public key. Pay-to-script-hash provides a means for complicated transactions, unlike the Pay-to-pubkey-hash, which has a specific definition for scriptPubKey, and scriptSig.

The specification places no limitations on the script, and hence absolutely any contract can be funded using these addresses. The scriptPubKey in the funding transaction is script which ensures that the script supplied in the redeeming transaction hashes to the script used to create the address.

In the scriptSig above, 'signatures' refers to any script which is sufficient to satisfy the following serialized script. Generations have a single input, and this input has a " coinbase " parameter instead of a scriptSig. The data in "coinbase" can be anything; it isn't used. Bitcoin puts the current compact-format target and the arbitrary-precision "extraNonce" number there, which increments every time the Nonce field in the block header overflows.

Outputs can be anything, but Bitcoin creates one exactly like an IP address transaction. The extranonce contributes to enlarge the domain for the proof of work function. Miners can easily modify nonce 4byte , timestamp and extranonce 2 to bytes. The input sufficiently describes where and how to get the bitcoin amout to be redeemed. If it is the only input of the first transaction of a block, it is called the generation transaction input and its content completely ignored.

Historically the Previous Transaction hash is 0 and the Previous Txout-index is The output sets the conditions to release this bitcoin amount later. The sum of the output values of the first transaction is the value of the mined bitcoins for the block plus possible transactions fees of the other transactions in the block. Retrieved from " https: Navigation menu Personal tools Create account Log in. Views Read View source View history. Sister projects Essays Source.

This page was last edited on 28 March , at Content is available under Creative Commons Attribution 3. Privacy policy About Bitcoin Wiki Disclaimers.