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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.
The 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 the stack. This document is for information purposes only. De facto, Bitcoin script is 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 False 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 anymore in the protocol , and 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, the 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 opcodes. 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 donate funds to miners in addition to transaction fees: This mechanism may be used in the future for fidelity bonds to sacrifice funds in a provable way.
Anyone-Can-Spend outputs are currently considered non-standard, and are not relayed on the P2P 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 data happened to be the Genesis block , and 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 the 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.
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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 against each remaining public key until it finds an ECDSA match.
The 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 keys 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 nSequence is not equal to or longer than the value of the top stack item.