Script: Difference between revisions
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Bitcoin uses a scripting system for [[transactions]]. [[Wikipedia:FORTH|Forth]]-like, Script is simple, stack-based, and processed from left to right. It is | Bitcoin uses a scripting system for [[transactions]]. [[Wikipedia:FORTH|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. | 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: the spender must provide | ||
# a public key that, when hashed, yields destination address D embedded in the script, and | |||
# a signature to prove ownership of the private key corresponding to the public key just provided. | |||
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 -1. | |||
0x80 is another representation of zero (so called negative 0). | |||
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 520 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. | |||
== Opcodes == | |||
This is a list of all Script words, also known as opcodes, commands, or functions. | |||
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. This fear was motivated by a bug found in OP_LSHIFT that could crash any Bitcoin node if exploited and by other bugs that allowed anyone to spend anyone's bitcoins. 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. | |||
New opcodes can be added by means of a carefully designed and executed [[softfork]] using OP_NOP1-OP_NOP10. | |||
Zero, negative zero (using any number of bytes), and empty array are all treated as false. Anything else is treated as true. | |||
=== Notation on this page === | |||
In the tables below, the inputs and outputs are both described by items as if they were pushed on the stack in that order. So for example, "x1 x2" indicates pushing value x1 on the stack, then x2, such that x1 is at the bottom of the stack, and x2 is at the top. When writing scripts as human-readable opcodes, the push opcodes and the associated data are usually written as <code><data></code>. For example, a P2SH script would be written as <code>OP_HASH160 <data> OP_EQUAL</code>, where <code><data></code> in this context means the byte <code>0x20</code> followed by the 20 bytes of the data itself. You should also ensure that you use the appropriate push instruction if your data is very large. See the table below for details. | |||
=== Constants === | === Constants === | ||
When talking about scripts, these value-pushing words are usually omitted. | |||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
!Input | !Input | ||
Line 339: | Line 46: | ||
!Description | !Description | ||
|- | |- | ||
|OP_FALSE | |OP_0, OP_FALSE | ||
|0 | |0 | ||
|0x00 | |0x00 | ||
|Nothing | |Nothing. | ||
| | |(empty value) | ||
| | |An empty array of bytes is pushed onto the stack. (This is not a no-op: an item is added to the stack.) | ||
|- | |- | ||
| | |N/A | ||
|1 - 75 | |1-75 | ||
|0x01 - 0x4b | |0x01-0x4b | ||
|( | |(special) | ||
| | |data | ||
|The next | |The next ''opcode'' bytes is data to be pushed onto the stack | ||
|- | |- | ||
|OP_PUSHDATA1 | |OP_PUSHDATA1 | ||
|76 | |76 | ||
|0x4c | |0x4c | ||
|( | |(special) | ||
| | |data | ||
|The next byte contains the number of bytes to be pushed onto the stack | |The next byte contains the number of bytes to be pushed onto the stack. | ||
|- | |- | ||
|OP_PUSHDATA2 | |OP_PUSHDATA2 | ||
|77 | |77 | ||
|0x4d | |0x4d | ||
|( | |(special) | ||
| | |data | ||
|The next two bytes contain the number of bytes to be pushed onto the stack | |The next two bytes contain the number of bytes to be pushed onto the stack in little endian order. | ||
|- | |- | ||
|OP_PUSHDATA4 | |OP_PUSHDATA4 | ||
|78 | |78 | ||
|0x4e | |0x4e | ||
|( | |(special) | ||
| | |data | ||
|The next four bytes contain the number of bytes to be pushed onto the stack | |The next four bytes contain the number of bytes to be pushed onto the stack in little endian order. | ||
|- | |- | ||
|OP_1NEGATE | |OP_1NEGATE | ||
|79 | |79 | ||
|0x4f | |0x4f | ||
|Nothing | |Nothing. | ||
| -1 | | -1 | ||
|The number -1 is pushed onto the stack. | |The number -1 is pushed onto the stack. | ||
Line 384: | Line 91: | ||
|81 | |81 | ||
|0x51 | |0x51 | ||
|Nothing | |Nothing. | ||
|1 | |1 | ||
|The number 1 is pushed onto the stack. | |The number 1 is pushed onto the stack. | ||
|- | |- | ||
|OP_2 - OP_16 | |OP_2-OP_16 | ||
|82 - 96 | |82-96 | ||
|0x52 - 0x60 | |0x52-0x60 | ||
|Nothing | |Nothing. | ||
|2-16 | |2-16 | ||
|The | |The number in the word name (2-16) is pushed onto the stack. | ||
|} | |} | ||
Line 400: | Line 107: | ||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
!Input | !Input | ||
Line 417: | Line 124: | ||
|99 | |99 | ||
|0x63 | |0x63 | ||
| | | colspan="2"|<expression> if [statements] [else [statements]]* endif | ||
| | |If the top stack value is not False, the statements are executed. The top stack value is removed. | ||
|If the top stack value is not | |||
|- | |- | ||
|OP_NOTIF | |OP_NOTIF | ||
|100 | |100 | ||
|0x64 | |0x64 | ||
| | | colspan="2"|<expression> notif [statements] [else [statements]]* endif | ||
| | |If the top stack value is False, the statements are executed. The top stack value is removed. | ||
|If the top stack value is | |||
|- | |- | ||
|OP_ELSE | |OP_ELSE | ||
|103 | |103 | ||
|0x67 | |0x67 | ||
| | | colspan="2"|<expression> if [statements] [else [statements]]* endif | ||
| | |If the preceding OP_IF or OP_NOTIF or OP_ELSE was not executed then these statements are and if the preceding OP_IF or OP_NOTIF or OP_ELSE was executed then these statements are not. | ||
|If the | |||
|- | |- | ||
|OP_ENDIF | |OP_ENDIF | ||
|104 | |104 | ||
|0x68 | |0x68 | ||
| | | colspan="2"|<expression> if [statements] [else [statements]]* endif | ||
|Ends an if/else block. All blocks must end, or the transaction is '''invalid'''. An OP_ENDIF without OP_IF earlier is also '''invalid'''. | |||
| | |||
|- | |- | ||
|OP_VERIFY | |OP_VERIFY | ||
|105 | |105 | ||
|0x69 | |0x69 | ||
| | |True / false | ||
|Nothing / | |Nothing / ''fail'' | ||
| | |'''Marks transaction as invalid''' if top stack value is not true. The top stack value is removed. | ||
|- | |- | ||
|OP_RETURN | |[[OP_RETURN]] | ||
|106 | |106 | ||
|0x6a | |0x6a | ||
|Nothing | |Nothing | ||
| | |''fail'' | ||
|Marks transaction as | |'''Marks transaction as invalid'''. Since bitcoin 0.9, a standard way of attaching extra data to transactions is to add a zero-value output with a scriptPubKey consisting of OP_RETURN followed by data. Such outputs are provably unspendable and specially discarded from storage in the UTXO set, reducing their cost to the network. Since [https://bitcoin.org/en/release/v0.12.0#relay-any-sequence-of-pushdatas-in-opreturn-outputs-now-allowed 0.12], standard relay rules allow a single output with OP_RETURN, that contains any sequence of push statements (or OP_RESERVED<ref>see code for IsPushOnly [https://github.com/bitcoin/bitcoin/blob/bccb4d29a8080bf1ecda1fc235415a11d903a680/src/script/script.cpp#L232]</ref>) after the OP_RETURN provided the total scriptPubKey length is at most 83 bytes. | ||
|} | |} | ||
Line 461: | Line 164: | ||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
!Input | !Input | ||
Line 471: | Line 174: | ||
|107 | |107 | ||
|0x6b | |0x6b | ||
|x1 | |x1 | ||
|(alt x1 | |(alt)x1 | ||
|Puts the input onto the top of the alt stack. Removes it from the | |Puts the input onto the top of the alt stack. Removes it from the main stack. | ||
|- | |- | ||
|OP_FROMALTSTACK | |OP_FROMALTSTACK | ||
|108 | |108 | ||
|0x6c | |0x6c | ||
|(alt x1 | |(alt)x1 | ||
|x1 | |x1 | ||
|Puts the input onto the top of the | |Puts the input onto the top of the main stack. Removes it from the alt stack. | ||
|- | |- | ||
|OP_IFDUP | |OP_IFDUP | ||
Line 535: | Line 196: | ||
|0x74 | |0x74 | ||
|Nothing | |Nothing | ||
| | |<Stack size> | ||
|Puts the number of stack items onto the stack | |Puts the number of stack items onto the stack. | ||
|- | |- | ||
|OP_DROP | |OP_DROP | ||
Line 585: | Line 246: | ||
|x1 x2 x3 | |x1 x2 x3 | ||
|x2 x3 x1 | |x2 x3 x1 | ||
|The | |The 3rd item down the stack is moved to the top. | ||
|- | |- | ||
|OP_SWAP | |OP_SWAP | ||
Line 600: | Line 261: | ||
|x2 x1 x2 | |x2 x1 x2 | ||
|The item at the top of the stack is copied and inserted before the second-to-top item. | |The item at the top of the stack is copied and inserted before the second-to-top item. | ||
|- | |||
|OP_2DROP | |||
|109 | |||
|0x6d | |||
|x1 x2 | |||
|Nothing | |||
|Removes the top two stack items. | |||
|- | |||
|OP_2DUP | |||
|110 | |||
|0x6e | |||
|x1 x2 | |||
|x1 x2 x1 x2 | |||
|Duplicates the top two stack items. | |||
|- | |||
|OP_3DUP | |||
|111 | |||
|0x6f | |||
|x1 x2 x3 | |||
|x1 x2 x3 x1 x2 x3 | |||
|Duplicates the top three stack items. | |||
|- | |||
|OP_2OVER | |||
|112 | |||
|0x70 | |||
|x1 x2 x3 x4 | |||
|x1 x2 x3 x4 x1 x2 | |||
|Copies the pair of items two spaces back in the stack to the front. | |||
|- | |||
|OP_2ROT | |||
|113 | |||
|0x71 | |||
|x1 x2 x3 x4 x5 x6 | |||
|x3 x4 x5 x6 x1 x2 | |||
|The fifth and sixth items back are moved to the top of the stack. | |||
|- | |||
|OP_2SWAP | |||
|114 | |||
|0x72 | |||
|x1 x2 x3 x4 | |||
|x3 x4 x1 x2 | |||
|Swaps the top two pairs of items. | |||
|} | |} | ||
=== Splice === | === Splice === | ||
If any opcode marked as disabled is present in a script, it must abort and fail. | |||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
!Input | !Input | ||
Line 618: | Line 323: | ||
|x1 x2 | |x1 x2 | ||
|out | |out | ||
|Concatenates two strings | |style="background:#D97171;"|Concatenates two strings. ''disabled.'' | ||
|- | |- | ||
|OP_SUBSTR | |OP_SUBSTR | ||
|127 | |127 | ||
|0x7f | |0x7f | ||
| | |in begin size | ||
|out | |out | ||
|Returns | |style="background:#D97171;"|Returns a section of a string. ''disabled.'' | ||
|- | |- | ||
|OP_LEFT | |OP_LEFT | ||
|128 | |128 | ||
|0x80 | |0x80 | ||
| | |in size | ||
|out | |out | ||
|Keeps only characters left of the specified point in a string. '' | |style="background:#D97171;"|Keeps only characters left of the specified point in a string. ''disabled.'' | ||
|- | |- | ||
|OP_RIGHT | |OP_RIGHT | ||
|129 | |129 | ||
|0x81 | |0x81 | ||
| | |in size | ||
|out | |out | ||
|Keeps only characters right of the specified point in a string. '' | |style="background:#D97171;"|Keeps only characters right of the specified point in a string. ''disabled.'' | ||
|- | |- | ||
|OP_SIZE | |OP_SIZE | ||
|130 | |130 | ||
|0x82 | |0x82 | ||
| | |in | ||
| | |in size | ||
| | |Pushes the string length of the top element of the stack (without popping it). | ||
|} | |} | ||
=== Bitwise logic === | === Bitwise logic === | ||
If any opcode marked as disabled is present in a script, it must abort and fail. | |||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
!Input | !Input | ||
Line 663: | Line 370: | ||
|131 | |131 | ||
|0x83 | |0x83 | ||
| | |in | ||
| | |out | ||
|Flips all of the bits in the input. '' | |style="background:#D97171;"|Flips all of the bits in the input. ''disabled.'' | ||
|- | |- | ||
|OP_AND | |OP_AND | ||
Line 671: | Line 378: | ||
|0x84 | |0x84 | ||
|x1 x2 | |x1 x2 | ||
| | |out | ||
|Boolean ''and'' between each bit in the inputs. '' | |style="background:#D97171;"|Boolean ''and'' between each bit in the inputs. ''disabled.'' | ||
|- | |- | ||
|OP_OR | |OP_OR | ||
Line 678: | Line 385: | ||
|0x85 | |0x85 | ||
|x1 x2 | |x1 x2 | ||
| | |out | ||
|Boolean ''or'' between each bit in the inputs. '' | |style="background:#D97171;"|Boolean ''or'' between each bit in the inputs. ''disabled.'' | ||
|- | |- | ||
|OP_XOR | |OP_XOR | ||
Line 685: | Line 392: | ||
|0x86 | |0x86 | ||
|x1 x2 | |x1 x2 | ||
| | |out | ||
|Boolean ''exclusive or'' between each bit in the inputs. '' | |style="background:#D97171;"|Boolean ''exclusive or'' between each bit in the inputs. ''disabled.'' | ||
|- | |- | ||
|OP_EQUAL | |OP_EQUAL | ||
Line 692: | Line 399: | ||
|0x87 | |0x87 | ||
|x1 x2 | |x1 x2 | ||
| | |True / false | ||
|Returns 1 if the inputs are | |Returns 1 if the inputs are exactly equal, 0 otherwise. | ||
|- | |- | ||
|OP_EQUALVERIFY | |OP_EQUALVERIFY | ||
Line 699: | Line 406: | ||
|0x88 | |0x88 | ||
|x1 x2 | |x1 x2 | ||
|Nothing / | |Nothing / ''fail'' | ||
|Same as OP_EQUAL, but runs OP_VERIFY afterward. | |Same as OP_EQUAL, but runs OP_VERIFY afterward. | ||
|} | |} | ||
Line 705: | Line 412: | ||
=== Arithmetic === | === Arithmetic === | ||
Note: Arithmetic inputs are limited to signed 32-bit integers, but may overflow their output. | |||
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. | |||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
!Input | !Input | ||
Line 719: | Line 429: | ||
|139 | |139 | ||
|0x8b | |0x8b | ||
| | |in | ||
| | |out | ||
|1 is added to the input. | |1 is added to the input. | ||
|- | |- | ||
Line 726: | Line 436: | ||
|140 | |140 | ||
|0x8c | |0x8c | ||
| | |in | ||
| | |out | ||
|1 is subtracted from the input. | |1 is subtracted from the input. | ||
|- | |- | ||
Line 733: | Line 443: | ||
|141 | |141 | ||
|0x8d | |0x8d | ||
| | |in | ||
| | |out | ||
|The input is multiplied by 2. '' | |style="background:#D97171;"|The input is multiplied by 2. ''disabled.'' | ||
|- | |- | ||
|OP_2DIV | |OP_2DIV | ||
|142 | |142 | ||
|0x8e | |0x8e | ||
| | |in | ||
| | |out | ||
|The input is divided by 2. '' | |style="background:#D97171;"|The input is divided by 2. ''disabled.'' | ||
|- | |- | ||
|OP_NEGATE | |OP_NEGATE | ||
|143 | |143 | ||
|0x8f | |0x8f | ||
| | |in | ||
| | |out | ||
|The sign of the input is flipped. | |The sign of the input is flipped. | ||
|- | |- | ||
Line 754: | Line 464: | ||
|144 | |144 | ||
|0x90 | |0x90 | ||
| | |in | ||
| | |out | ||
|The input is | |The input is made positive. | ||
|- | |- | ||
|OP_NOT | |OP_NOT | ||
|145 | |145 | ||
|0x91 | |0x91 | ||
| | |in | ||
| | |out | ||
|If the input is 0 or 1, it is flipped. Otherwise the output will be 0. | |If the input is 0 or 1, it is flipped. Otherwise the output will be 0. | ||
|- | |- | ||
Line 768: | Line 478: | ||
|146 | |146 | ||
|0x92 | |0x92 | ||
| | |in | ||
| | |out | ||
|Returns 0 if the input is 0. 1 otherwise. | |Returns 0 if the input is 0. 1 otherwise. | ||
|- | |- | ||
Line 776: | Line 486: | ||
|0x93 | |0x93 | ||
|a b | |a b | ||
| | |out | ||
|a is added to b. | |a is added to b. | ||
|- | |- | ||
Line 783: | Line 493: | ||
|0x94 | |0x94 | ||
|a b | |a b | ||
| | |out | ||
|b is subtracted from a. | |b is subtracted from a. | ||
|- | |- | ||
Line 790: | Line 500: | ||
|0x95 | |0x95 | ||
|a b | |a b | ||
| | |out | ||
|a is multiplied by b. '' | |style="background:#D97171;"|a is multiplied by b. ''disabled.'' | ||
|- | |- | ||
|OP_DIV | |OP_DIV | ||
Line 797: | Line 507: | ||
|0x96 | |0x96 | ||
|a b | |a b | ||
| | |out | ||
|a is divided by b | |style="background:#D97171;"|a is divided by b. ''disabled.'' | ||
|- | |- | ||
|OP_MOD | |OP_MOD | ||
Line 804: | Line 514: | ||
|0x97 | |0x97 | ||
|a b | |a b | ||
| | |out | ||
|Returns the remainder after dividing a by b | |style="background:#D97171;"|Returns the remainder after dividing a by b. ''disabled.'' | ||
|- | |- | ||
|OP_LSHIFT | |OP_LSHIFT | ||
Line 811: | Line 521: | ||
|0x98 | |0x98 | ||
|a b | |a b | ||
| | |out | ||
|Shifts a left | |style="background:#D97171;"|Shifts a left b bits, preserving sign. ''disabled.'' | ||
|- | |- | ||
|OP_RSHIFT | |OP_RSHIFT | ||
Line 818: | Line 528: | ||
|0x99 | |0x99 | ||
|a b | |a b | ||
| | |out | ||
|Shifts a right | |style="background:#D97171;"|Shifts a right b bits, preserving sign. ''disabled.'' | ||
|- | |- | ||
|OP_BOOLAND | |OP_BOOLAND | ||
Line 825: | Line 535: | ||
|0x9a | |0x9a | ||
|a b | |a b | ||
| | |out | ||
|If both a and b are not 0, the output is 1. Otherwise 0. | |If both a and b are not 0, the output is 1. Otherwise 0. | ||
|- | |- | ||
Line 832: | Line 542: | ||
|0x9b | |0x9b | ||
|a b | |a b | ||
| | |out | ||
|If a or b is not 0, the output is 1. Otherwise 0. | |If a or b is not 0, the output is 1. Otherwise 0. | ||
|- | |- | ||
Line 839: | Line 549: | ||
|0x9c | |0x9c | ||
|a b | |a b | ||
| | |out | ||
|Returns 1 if the numbers are equal, 0 otherwise. | |Returns 1 if the numbers are equal, 0 otherwise. | ||
|- | |- | ||
Line 846: | Line 556: | ||
|0x9d | |0x9d | ||
|a b | |a b | ||
|Nothing / | |Nothing / ''fail'' | ||
|Same as OP_NUMEQUAL, but runs OP_VERIFY afterward. | |Same as OP_NUMEQUAL, but runs OP_VERIFY afterward. | ||
|- | |- | ||
Line 853: | Line 563: | ||
|0x9e | |0x9e | ||
|a b | |a b | ||
| | |out | ||
|Returns 1 if the numbers are not equal, 0 otherwise. | |Returns 1 if the numbers are not equal, 0 otherwise. | ||
|- | |- | ||
Line 860: | Line 570: | ||
|0x9f | |0x9f | ||
|a b | |a b | ||
| | |out | ||
|Returns 1 if a is less than b, 0 otherwise. | |Returns 1 if a is less than b, 0 otherwise. | ||
|- | |- | ||
Line 867: | Line 577: | ||
|0xa0 | |0xa0 | ||
|a b | |a b | ||
| | |out | ||
|Returns 1 if a is greater than b, 0 otherwise. | |Returns 1 if a is greater than b, 0 otherwise. | ||
|- | |- | ||
Line 874: | Line 584: | ||
|0xa1 | |0xa1 | ||
|a b | |a b | ||
| | |out | ||
|Returns 1 if a is less than or equal to b, 0 otherwise. | |Returns 1 if a is less than or equal to b, 0 otherwise. | ||
|- | |- | ||
Line 881: | Line 591: | ||
|0xa2 | |0xa2 | ||
|a b | |a b | ||
| | |out | ||
|Returns 1 if a is greater than or equal to b, 0 otherwise. | |Returns 1 if a is greater than or equal to b, 0 otherwise. | ||
|- | |- | ||
Line 888: | Line 598: | ||
|0xa3 | |0xa3 | ||
|a b | |a b | ||
| | |out | ||
|Returns the smaller of a and b. | |Returns the smaller of a and b. | ||
|- | |- | ||
Line 895: | Line 605: | ||
|0xa4 | |0xa4 | ||
|a b | |a b | ||
| | |out | ||
|Returns the larger of a and b. | |Returns the larger of a and b. | ||
|- | |- | ||
Line 902: | Line 612: | ||
|0xa5 | |0xa5 | ||
|x min max | |x min max | ||
| | |out | ||
|Returns 1 if x is within the specified range (left-inclusive) , 0 otherwise. | |Returns 1 if x is within the specified range (left-inclusive), 0 otherwise. | ||
|} | |} | ||
Line 910: | Line 620: | ||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
!Input | !Input | ||
Line 920: | Line 630: | ||
|166 | |166 | ||
|0xa6 | |0xa6 | ||
| | |in | ||
| | |hash | ||
|The input is hashed using RIPEMD-160. | |The input is hashed using RIPEMD-160. | ||
|- | |- | ||
Line 927: | Line 637: | ||
|167 | |167 | ||
|0xa7 | |0xa7 | ||
| | |in | ||
| | |hash | ||
|The input is hashed using SHA-1. | |The input is hashed using SHA-1. | ||
|- | |- | ||
Line 934: | Line 644: | ||
|168 | |168 | ||
|0xa8 | |0xa8 | ||
| | |in | ||
| | |hash | ||
|The input is hashed using SHA-256. | |The input is hashed using SHA-256. | ||
|- | |- | ||
Line 941: | Line 651: | ||
|169 | |169 | ||
|0xa9 | |0xa9 | ||
| | |in | ||
| | |hash | ||
|The input is hashed twice: first with SHA-256 and then with RIPEMD-160. | |The input is hashed twice: first with SHA-256 and then with RIPEMD-160. | ||
|- | |- | ||
Line 948: | Line 658: | ||
|170 | |170 | ||
|0xaa | |0xaa | ||
| | |in | ||
| | |hash | ||
|The input is hashed two times with SHA-256. | |The input is hashed two times with SHA-256. | ||
|- | |- | ||
Line 957: | Line 667: | ||
|Nothing | |Nothing | ||
|Nothing | |Nothing | ||
|All of the signature checking | |All of the signature checking words will only match signatures to the data after the most recently-executed OP_CODESEPARATOR. | ||
|- | |- | ||
|[[OP_CHECKSIG]] | |[[OP_CHECKSIG]] | ||
Line 963: | Line 673: | ||
|0xac | |0xac | ||
|sig pubkey | |sig pubkey | ||
| | |True / false | ||
|The entire transaction's outputs, inputs, and script (from the most recently-executed OP_CODESEPARATOR to the end) are hashed. The signature used by OP_CHECKSIG must be a valid signature for | |The entire transaction's outputs, inputs, and script (from the most recently-executed OP_CODESEPARATOR to the end) are hashed. The signature used by OP_CHECKSIG must be a valid signature for this hash and public key. If it is, 1 is returned, 0 otherwise. | ||
|- | |- | ||
|OP_CHECKSIGVERIFY | |OP_CHECKSIGVERIFY | ||
Line 970: | Line 680: | ||
|0xad | |0xad | ||
|sig pubkey | |sig pubkey | ||
|Nothing / | |Nothing / ''fail'' | ||
|Same as OP_CHECKSIG, but OP_VERIFY is executed afterward. | |Same as OP_CHECKSIG, but OP_VERIFY is executed afterward. | ||
|- | |- | ||
Line 976: | Line 686: | ||
|174 | |174 | ||
|0xae | |0xae | ||
|sig1 sig2 ... <number of signatures> pub1 pub2 <number of public keys> | |x sig1 sig2 ... <number of signatures> pub1 pub2 <number of public keys> | ||
| | |True / False | ||
| | |Compares the first signature against each public key until it finds an ECDSA match. 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. | ||
|- | |- | ||
|OP_CHECKMULTISIGVERIFY | |OP_CHECKMULTISIGVERIFY | ||
|175 | |175 | ||
|0xaf | |0xaf | ||
|sig1 sig2 ... <number of signatures> pub1 pub2 ... <number of public keys> | |x sig1 sig2 ... <number of signatures> pub1 pub2 ... <number of public keys> | ||
|Nothing / | |Nothing / ''fail'' | ||
|Same as OP_CHECKMULTISIG, but OP_VERIFY is executed afterward. | |Same as OP_CHECKMULTISIG, but OP_VERIFY is executed afterward. | ||
|- | |- | ||
|OP_CHECKSIGADD | |||
|186 | |||
|0xba | |||
|sig n pub | |||
| | |out | ||
| | |Three values are popped from the stack. The integer n is incremented by one and returned to the stack if the signature is valid for the public key and transaction. The integer n is returned to the stack unchanged if the signature is the empty vector (OP_0). In any other case, the script is invalid. This opcode is only available in tapscript.<ref>[https://github.com/bitcoin/bips/blob/master/bip-0342.mediawiki BIP342]</ref> | ||
| | |||
| | |||
|The opcode | |||
|} | |} | ||
=== | === Locktime === | ||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
!Input | |||
!Output | |||
!Description | !Description | ||
|- | |- | ||
| | |OP_CHECKLOCKTIMEVERIFY (previously OP_NOP2) | ||
| | |177 | ||
| | |0xb1 | ||
| | |x | ||
|x / ''fail'' | |||
|'''Marks transaction as invalid''' if the top stack item is greater than the transaction's nLockTime field, otherwise script evaluation continues as though an OP_NOP was executed. Transaction is also invalid if 1. the stack is empty; or 2. the top stack item is negative; or 3. the top stack item is greater than or equal to 500000000 while the transaction's nLockTime field is less than 500000000, or vice versa; or 4. the input's nSequence field is equal to 0xffffffff. The precise semantics are described in [https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki BIP 0065]. | |||
|- | |- | ||
| | |OP_CHECKSEQUENCEVERIFY (previously OP_NOP3) | ||
| | |178 | ||
| | |0xb2 | ||
| | |x | ||
| | |x / ''fail'' | ||
| | |'''Marks transaction as invalid''' if the relative lock time of the input (enforced by [https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki BIP 0068] with nSequence) is not equal to or longer than the value of the top stack item. The precise semantics are described in [https://github.com/bitcoin/bips/blob/master/bip-0112.mediawiki BIP 0112]. | ||
|} | |} | ||
=== Reserved | |||
=== Reserved words === | |||
Any opcode not assigned is also reserved. Using an unassigned opcode makes the transaction '''invalid'''. | |||
{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
! | !Word | ||
! | !Opcode | ||
!Hex | !Hex | ||
! | !When used... | ||
|- | |- | ||
|OP_RESERVED | |OP_RESERVED | ||
|80 | |80 | ||
|0x50 | |0x50 | ||
| | |'''Transaction is invalid''' unless occuring in an unexecuted OP_IF branch | ||
|- | |- | ||
|OP_VER | |OP_VER | ||
|98 | |98 | ||
|0x62 | |0x62 | ||
| | |'''Transaction is invalid''' unless occuring in an unexecuted OP_IF branch | ||
|- | |- | ||
|OP_VERIF | |OP_VERIF | ||
|101 | |101 | ||
|0x65 | |0x65 | ||
| | |'''Transaction is invalid even when occuring in an unexecuted OP_IF branch''' | ||
|- | |- | ||
|OP_VERNOTIF | |OP_VERNOTIF | ||
|102 | |102 | ||
|0x66 | |0x66 | ||
| | |'''Transaction is invalid even when occuring in an unexecuted OP_IF branch''' | ||
|- | |- | ||
|OP_RESERVED1 | |OP_RESERVED1 | ||
|137 | |137 | ||
|0x89 | |0x89 | ||
| | |'''Transaction is invalid''' unless occuring in an unexecuted OP_IF branch | ||
|- | |- | ||
|OP_RESERVED2 | |OP_RESERVED2 | ||
|138 | |138 | ||
|0x8a | |0x8a | ||
| | |'''Transaction is invalid''' unless occuring in an unexecuted OP_IF branch | ||
|- | |||
|OP_NOP1, OP_NOP4-OP_NOP10 | |||
|176, 179-185 | |||
|0xb0, 0xb3-0xb9 | |||
|The word is ignored. Does not mark transaction as invalid. | |||
|} | |} | ||
== | == Script examples == | ||
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. | |||
These examples include the “OP_” prefix, but it is permissible to omit it. | |||
Thus | |||
“<pubkey1> <pubkey2> OP_2 OP_CHECKMULTISIG” | |||
may be abbreviated to | |||
“<pubkey1> <pubkey2> 2 CHECKMULTISIG”. | |||
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. | |||
=== Standard Transaction to Bitcoin address === | === Standard Transaction to Bitcoin address (pay-to-pubkey-hash) === | ||
scriptPubKey: OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | scriptPubKey: OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | ||
Line 1,121: | Line 840: | ||
|} | |} | ||
=== | === Obsolete pay-to-pubkey transaction === | ||
OP_CHECKSIG is used directly without first hashing the public key. | |||
This was used by early versions of Bitcoin where people paid directly to IP addresses, before Bitcoin addresses were introduced. | |||
scriptPubKeys of this transaction form are still recognized as payments to user by Bitcoin Core. | |||
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. | |||
scriptPubKey: <pubKey> OP_CHECKSIG | scriptPubKey: <pubKey> OP_CHECKSIG | ||
Line 1,146: | Line 870: | ||
|} | |} | ||
=== | === Provably Unspendable/Prunable Outputs === | ||
The standard way to mark a transaction as provably unspendable is with a scriptPubKey of the following form: | |||
scriptPubKey: OP_RETURN {zero or more ops} | |||
OP_RETURN immediately marks the script as invalid, guaranteeing that no scriptSig exists that could possibly spend that output. Thus the output can be immediately pruned from the [[UTXO|UTXO set]] even if it has not been spent. [http://blockexplorer.com/tx/eb31ca1a4cbd97c2770983164d7560d2d03276ae1aee26f12d7c2c6424252f29 eb31ca1a4cbd97c2770983164d7560d2d03276ae1aee26f12d7c2c6424252f29] is an example: it has a single output of zero value, thus giving the full 0.125BTC fee to the miner who mined the transaction without adding an entry to the UTXO set. You can also use OP_RETURN to add data to a transaction without the data ever appearing in the UTXO set, as seen in 1a2e22a717d626fc5db363582007c46924ae6b28319f07cb1b907776bd8293fc; [[P2Pool]] does this with the share chain hash txout in the coinbase of blocks it creates. | |||
scriptPubKey: < | |||
scriptSig: <sig> | === Freezing funds until a time in the future === | ||
Using OP_CHECKLOCKTIMEVERIFY it is possible to make funds provably unspendable until a certain point in the future. | |||
scriptPubKey: <expiry time> OP_CHECKLOCKTIMEVERIFY OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | |||
scriptSig: <sig> <pubKey> | |||
{| class="wikitable" | {| class="wikitable" | ||
Line 1,159: | Line 892: | ||
|- | |- | ||
|Empty. | |Empty. | ||
|<sig> < | | <sig> <pubKey> <expiry time> OP_CHECKLOCKTIMEVERIFY OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | ||
| | | scriptSig and scriptPubKey are combined. | ||
|- | |||
|<sig> <pubKey> <expiry time> | |||
| OP_CHECKLOCKTIMEVERIFY OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | |||
| Constants are added to the stack. | |||
|- | |||
|<sig> <pubKey> <expiry time> | |||
| OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | |||
| Top stack item is checked against the current time or block height. | |||
|- | |||
|<sig> <pubKey> | |||
| OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | |||
| Top stack item is removed. | |||
|- | |- | ||
|<sig> | |<sig> <pubKey> <pubKey> | ||
| OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | |||
| | | Top stack item is duplicated. | ||
|- | |- | ||
|<sig> < | |<sig> <pubKey> <pubHashA> | ||
| | |<pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | ||
| | | Top stack item is hashed. | ||
|- | |- | ||
|<sig> | |<sig> <pubKey> <pubHashA> <pubKeyHash> | ||
|OP_EQUALVERIFY OP_CHECKSIG | |||
| | | Constant added. | ||
|- | |- | ||
|<sig> <pubKey> | |<sig> <pubKey> | ||
|OP_CHECKSIG | |OP_CHECKSIG | ||
| | | Equality is checked between the top two stack items. | ||
|- | |- | ||
|true | |true | ||
|Empty. | |Empty. | ||
| | |Signature is checked for top two stack items. | ||
|} | |} | ||
=== | === Transaction puzzle === | ||
Transaction a4bfa8ab6435ae5f25dae9d89e4eb67dfa94283ca751f393c1ddc5a837bbc31b is an interesting puzzle. | |||
scriptPubKey: OP_HASH256 6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000 OP_EQUAL | |||
scriptSig: <data> | |||
To spend the transaction you need to come up with some data such that hashing the data twice results in the given hash. | |||
= | {| class="wikitable" | ||
|- | |||
< | ! Stack | ||
< | ! Script | ||
< | ! Description | ||
|- | |||
< | |Empty. | ||
< | |<data> OP_HASH256 <given_hash> OP_EQUAL | ||
< | | | ||
< | |- | ||
|<data> | |||
|OP_HASH256 <given_hash> OP_EQUAL | |||
|scriptSig added to the stack. | |||
|- | |||
|<data_hash> | |||
|<given_hash> OP_EQUAL | |||
|The data is hashed. | |||
|- | |||
< | |<data_hash> <given_hash> | ||
< | |OP_EQUAL | ||
< | |The given hash is pushed to the stack. | ||
< | |- | ||
|true | |||
|Empty. | |||
|The hashes are compared, leaving true on the stack. | |||
|} | |||
This transaction was successfully spent by 09f691b2263260e71f363d1db51ff3100d285956a40cc0e4f8c8c2c4a80559b1. 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-256. 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. | |||
=== Incentivized finding of hash collisions === | |||
In 2013 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. | |||
For example the SHA1 script: | |||
scriptPubKey: OP_2DUP OP_EQUAL OP_NOT OP_VERIFY OP_SHA1 OP_SWAP OP_SHA1 OP_EQUAL | |||
scriptSig: <preimage1> <preimage2> | |||
See the bitcointalk thread <ref>[https://bitcointalk.org/index.php?topic=293382.0 bitcointalk forum thread on the hash collision bounties]</ref> and reddit thread<ref>https://www.reddit.com/r/Bitcoin/comments/1mavh9/trustless_bitcoin_bounty_for_sha1_sha256_etc/</ref> for more details. | |||
In February 2017 the SHA1 bounty worth 2.48 bitcoins was claimed. | |||
==See Also== | ==See Also== | ||
Line 1,223: | Line 983: | ||
* [[Transactions]] | * [[Transactions]] | ||
* [[Contracts]] | * [[Contracts]] | ||
== External Links == | |||
*[https://bitide.qedprotocol.com/ BitIDE] - BitIDE: A web based Bitcoin Script IDE with built in debugger, meta-scripting, virtual op-codes, and local testnet. | |||
*[https://bitcoin.sipa.be/miniscript] - Miniscript: a language for writing (a subset of) Bitcoin Scripts in a structured way, enabling analysis, composition, generic signing and more. | |||
*[https://github.com/siminchen/bitcoinIDE Bitcoin IDE] – Bitcoin Script for dummies | |||
*[https://webbtc.com/script Bitcoin Debug Script Execution] – web tool which executes a script opcode-by-opcode | |||
*[http://www.crmarsh.com/script-playground/ Script Playground] — convert Script to JavaScript | |||
*[https://bitauth.com/ide BitAuth IDE] — an Integrated Development Environment for Bitcoin Authentication | |||
<sup>(cf. "[http://bitcoin.stackexchange.com/q/42576/4334 Online Bitcoin Script simulator or debugger?]")</sup> | |||
==References== | ==References== | ||
Line 1,229: | Line 998: | ||
[[Category:Technical]] | [[Category:Technical]] | ||
[[Category:Vocabulary]] | [[Category:Vocabulary]] | ||
{{Bitcoin Core documentation}} |
Revision as of 22:25, 26 April 2024
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: the spender must provide
- a public key that, when hashed, yields destination address D embedded in the script, and
- a signature to prove ownership of the private key corresponding to the public key just provided.
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 -1. 0x80 is another representation of zero (so called negative 0). 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 520 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.
Opcodes
This is a list of all Script words, also known as opcodes, commands, or functions.
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. This fear was motivated by a bug found in OP_LSHIFT that could crash any Bitcoin node if exploited and by other bugs that allowed anyone to spend anyone's bitcoins. 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.
New opcodes can be added by means of a carefully designed and executed softfork using OP_NOP1-OP_NOP10.
Zero, negative zero (using any number of bytes), and empty array are all treated as false. Anything else is treated as true.
Notation on this page
In the tables below, the inputs and outputs are both described by items as if they were pushed on the stack in that order. So for example, "x1 x2" indicates pushing value x1 on the stack, then x2, such that x1 is at the bottom of the stack, and x2 is at the top. When writing scripts as human-readable opcodes, the push opcodes and the associated data are usually written as <data>
. For example, a P2SH script would be written as OP_HASH160 <data> OP_EQUAL
, where <data>
in this context means the byte 0x20
followed by the 20 bytes of the data itself. You should also ensure that you use the appropriate push instruction if your data is very large. See the table below for details.
Constants
When talking about scripts, these value-pushing words are usually omitted.
Word | Opcode | Hex | Input | Output | Description |
---|---|---|---|---|---|
OP_0, OP_FALSE | 0 | 0x00 | Nothing. | (empty value) | An empty array of bytes is pushed onto the stack. (This is not a no-op: an item is added to the stack.) |
N/A | 1-75 | 0x01-0x4b | (special) | data | The next opcode bytes is data to be pushed onto the stack |
OP_PUSHDATA1 | 76 | 0x4c | (special) | data | The next byte contains the number of bytes to be pushed onto the stack. |
OP_PUSHDATA2 | 77 | 0x4d | (special) | data | The next two bytes contain the number of bytes to be pushed onto the stack in little endian order. |
OP_PUSHDATA4 | 78 | 0x4e | (special) | data | The next four bytes contain the number of bytes to be pushed onto the stack in little endian order. |
OP_1NEGATE | 79 | 0x4f | Nothing. | -1 | The number -1 is pushed onto the stack. |
OP_1, OP_TRUE | 81 | 0x51 | Nothing. | 1 | The number 1 is pushed onto the stack. |
OP_2-OP_16 | 82-96 | 0x52-0x60 | Nothing. | 2-16 | The number in the word name (2-16) is pushed onto the stack. |
Flow control
Word | Opcode | Hex | Input | Output | Description |
---|---|---|---|---|---|
OP_NOP | 97 | 0x61 | Nothing | Nothing | Does nothing. |
OP_IF | 99 | 0x63 | <expression> if [statements] [else [statements]]* endif | If the top stack value is not False, the statements are executed. The top stack value is removed. | |
OP_NOTIF | 100 | 0x64 | <expression> notif [statements] [else [statements]]* endif | If the top stack value is False, the statements are executed. The top stack value is removed. | |
OP_ELSE | 103 | 0x67 | <expression> if [statements] [else [statements]]* endif | If the preceding OP_IF or OP_NOTIF or OP_ELSE was not executed then these statements are and if the preceding OP_IF or OP_NOTIF or OP_ELSE was executed then these statements are not. | |
OP_ENDIF | 104 | 0x68 | <expression> if [statements] [else [statements]]* endif | Ends an if/else block. All blocks must end, or the transaction is invalid. An OP_ENDIF without OP_IF earlier is also invalid. | |
OP_VERIFY | 105 | 0x69 | True / false | Nothing / fail | Marks transaction as invalid if top stack value is not true. The top stack value is removed. |
OP_RETURN | 106 | 0x6a | Nothing | fail | Marks transaction as invalid. Since bitcoin 0.9, a standard way of attaching extra data to transactions is to add a zero-value output with a scriptPubKey consisting of OP_RETURN followed by data. Such outputs are provably unspendable and specially discarded from storage in the UTXO set, reducing their cost to the network. Since 0.12, standard relay rules allow a single output with OP_RETURN, that contains any sequence of push statements (or OP_RESERVED[1]) after the OP_RETURN provided the total scriptPubKey length is at most 83 bytes. |
Stack
Word | Opcode | Hex | Input | Output | Description |
---|---|---|---|---|---|
OP_TOALTSTACK | 107 | 0x6b | x1 | (alt)x1 | Puts the input onto the top of the alt stack. Removes it from the main stack. |
OP_FROMALTSTACK | 108 | 0x6c | (alt)x1 | x1 | Puts the input onto the top of the main stack. Removes it from the alt stack. |
OP_IFDUP | 115 | 0x73 | x | x / x x | If the top stack value is not 0, duplicate it. |
OP_DEPTH | 116 | 0x74 | Nothing | <Stack size> | Puts the number of stack items onto the stack. |
OP_DROP | 117 | 0x75 | x | Nothing | Removes the top stack item. |
OP_DUP | 118 | 0x76 | x | x x | Duplicates the top stack item. |
OP_NIP | 119 | 0x77 | x1 x2 | x2 | Removes the second-to-top stack item. |
OP_OVER | 120 | 0x78 | x1 x2 | x1 x2 x1 | Copies the second-to-top stack item to the top. |
OP_PICK | 121 | 0x79 | xn ... x2 x1 x0 <n> | xn ... x2 x1 x0 xn | The item n back in the stack is copied to the top. |
OP_ROLL | 122 | 0x7a | xn ... x2 x1 x0 <n> | ... x2 x1 x0 xn | The item n back in the stack is moved to the top. |
OP_ROT | 123 | 0x7b | x1 x2 x3 | x2 x3 x1 | The 3rd item down the stack is moved to the top. |
OP_SWAP | 124 | 0x7c | x1 x2 | x2 x1 | The top two items on the stack are swapped. |
OP_TUCK | 125 | 0x7d | x1 x2 | x2 x1 x2 | The item at the top of the stack is copied and inserted before the second-to-top item. |
OP_2DROP | 109 | 0x6d | x1 x2 | Nothing | Removes the top two stack items. |
OP_2DUP | 110 | 0x6e | x1 x2 | x1 x2 x1 x2 | Duplicates the top two stack items. |
OP_3DUP | 111 | 0x6f | x1 x2 x3 | x1 x2 x3 x1 x2 x3 | Duplicates the top three stack items. |
OP_2OVER | 112 | 0x70 | x1 x2 x3 x4 | x1 x2 x3 x4 x1 x2 | Copies the pair of items two spaces back in the stack to the front. |
OP_2ROT | 113 | 0x71 | x1 x2 x3 x4 x5 x6 | x3 x4 x5 x6 x1 x2 | The fifth and sixth items back are moved to the top of the stack. |
OP_2SWAP | 114 | 0x72 | x1 x2 x3 x4 | x3 x4 x1 x2 | Swaps the top two pairs of items. |
Splice
If any opcode marked as disabled is present in a script, it must abort and fail.
Word | Opcode | Hex | Input | Output | Description |
---|---|---|---|---|---|
OP_CAT | 126 | 0x7e | x1 x2 | out | Concatenates two strings. disabled. |
OP_SUBSTR | 127 | 0x7f | in begin size | out | Returns a section of a string. disabled. |
OP_LEFT | 128 | 0x80 | in size | out | Keeps only characters left of the specified point in a string. disabled. |
OP_RIGHT | 129 | 0x81 | in size | out | Keeps only characters right of the specified point in a string. disabled. |
OP_SIZE | 130 | 0x82 | in | in size | Pushes the string length of the top element of the stack (without popping it). |
Bitwise logic
If any opcode marked as disabled is present in a script, it must abort and fail.
Word | Opcode | Hex | Input | Output | Description |
---|---|---|---|---|---|
OP_INVERT | 131 | 0x83 | in | out | Flips all of the bits in the input. disabled. |
OP_AND | 132 | 0x84 | x1 x2 | out | Boolean and between each bit in the inputs. disabled. |
OP_OR | 133 | 0x85 | x1 x2 | out | Boolean or between each bit in the inputs. disabled. |
OP_XOR | 134 | 0x86 | x1 x2 | out | Boolean exclusive or between each bit in the inputs. disabled. |
OP_EQUAL | 135 | 0x87 | x1 x2 | True / false | Returns 1 if the inputs are exactly equal, 0 otherwise. |
OP_EQUALVERIFY | 136 | 0x88 | x1 x2 | Nothing / fail | Same as OP_EQUAL, but runs OP_VERIFY afterward. |
Arithmetic
Note: Arithmetic inputs are limited to signed 32-bit integers, but may overflow their output.
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.
Word | Opcode | Hex | Input | Output | Description |
---|---|---|---|---|---|
OP_1ADD | 139 | 0x8b | in | out | 1 is added to the input. |
OP_1SUB | 140 | 0x8c | in | out | 1 is subtracted from the input. |
OP_2MUL | 141 | 0x8d | in | out | The input is multiplied by 2. disabled. |
OP_2DIV | 142 | 0x8e | in | out | The input is divided by 2. disabled. |
OP_NEGATE | 143 | 0x8f | in | out | The sign of the input is flipped. |
OP_ABS | 144 | 0x90 | in | out | The input is made positive. |
OP_NOT | 145 | 0x91 | in | out | If the input is 0 or 1, it is flipped. Otherwise the output will be 0. |
OP_0NOTEQUAL | 146 | 0x92 | in | out | Returns 0 if the input is 0. 1 otherwise. |
OP_ADD | 147 | 0x93 | a b | out | a is added to b. |
OP_SUB | 148 | 0x94 | a b | out | b is subtracted from a. |
OP_MUL | 149 | 0x95 | a b | out | a is multiplied by b. disabled. |
OP_DIV | 150 | 0x96 | a b | out | a is divided by b. disabled. |
OP_MOD | 151 | 0x97 | a b | out | Returns the remainder after dividing a by b. disabled. |
OP_LSHIFT | 152 | 0x98 | a b | out | Shifts a left b bits, preserving sign. disabled. |
OP_RSHIFT | 153 | 0x99 | a b | out | Shifts a right b bits, preserving sign. disabled. |
OP_BOOLAND | 154 | 0x9a | a b | out | If both a and b are not 0, the output is 1. Otherwise 0. |
OP_BOOLOR | 155 | 0x9b | a b | out | If a or b is not 0, the output is 1. Otherwise 0. |
OP_NUMEQUAL | 156 | 0x9c | a b | out | Returns 1 if the numbers are equal, 0 otherwise. |
OP_NUMEQUALVERIFY | 157 | 0x9d | a b | Nothing / fail | Same as OP_NUMEQUAL, but runs OP_VERIFY afterward. |
OP_NUMNOTEQUAL | 158 | 0x9e | a b | out | Returns 1 if the numbers are not equal, 0 otherwise. |
OP_LESSTHAN | 159 | 0x9f | a b | out | Returns 1 if a is less than b, 0 otherwise. |
OP_GREATERTHAN | 160 | 0xa0 | a b | out | Returns 1 if a is greater than b, 0 otherwise. |
OP_LESSTHANOREQUAL | 161 | 0xa1 | a b | out | Returns 1 if a is less than or equal to b, 0 otherwise. |
OP_GREATERTHANOREQUAL | 162 | 0xa2 | a b | out | Returns 1 if a is greater than or equal to b, 0 otherwise. |
OP_MIN | 163 | 0xa3 | a b | out | Returns the smaller of a and b. |
OP_MAX | 164 | 0xa4 | a b | out | Returns the larger of a and b. |
OP_WITHIN | 165 | 0xa5 | x min max | out | Returns 1 if x is within the specified range (left-inclusive), 0 otherwise. |
Crypto
Word | Opcode | Hex | Input | Output | Description |
---|---|---|---|---|---|
OP_RIPEMD160 | 166 | 0xa6 | in | hash | The input is hashed using RIPEMD-160. |
OP_SHA1 | 167 | 0xa7 | in | hash | The input is hashed using SHA-1. |
OP_SHA256 | 168 | 0xa8 | in | hash | The input is hashed using SHA-256. |
OP_HASH160 | 169 | 0xa9 | in | hash | The input is hashed twice: first with SHA-256 and then with RIPEMD-160. |
OP_HASH256 | 170 | 0xaa | in | hash | The input is hashed two times with SHA-256. |
OP_CODESEPARATOR | 171 | 0xab | Nothing | Nothing | All of the signature checking words will only match signatures to the data after the most recently-executed OP_CODESEPARATOR. |
OP_CHECKSIG | 172 | 0xac | sig pubkey | True / false | The entire transaction's outputs, inputs, and script (from the most recently-executed OP_CODESEPARATOR to the end) are hashed. The signature used by OP_CHECKSIG must be a valid signature for this hash and public key. If it is, 1 is returned, 0 otherwise. |
OP_CHECKSIGVERIFY | 173 | 0xad | sig pubkey | Nothing / fail | Same as OP_CHECKSIG, but OP_VERIFY is executed afterward. |
OP_CHECKMULTISIG | 174 | 0xae | x sig1 sig2 ... <number of signatures> pub1 pub2 <number of public keys> | True / False | Compares the first signature against each public key until it finds an ECDSA match. 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. |
OP_CHECKMULTISIGVERIFY | 175 | 0xaf | x sig1 sig2 ... <number of signatures> pub1 pub2 ... <number of public keys> | Nothing / fail | Same as OP_CHECKMULTISIG, but OP_VERIFY is executed afterward. |
OP_CHECKSIGADD | 186 | 0xba | sig n pub | out | Three values are popped from the stack. The integer n is incremented by one and returned to the stack if the signature is valid for the public key and transaction. The integer n is returned to the stack unchanged if the signature is the empty vector (OP_0). In any other case, the script is invalid. This opcode is only available in tapscript.[2] |
Locktime
Word | Opcode | Hex | Input | Output | Description |
---|---|---|---|---|---|
OP_CHECKLOCKTIMEVERIFY (previously OP_NOP2) | 177 | 0xb1 | x | x / fail | Marks transaction as invalid if the top stack item is greater than the transaction's nLockTime field, otherwise script evaluation continues as though an OP_NOP was executed. Transaction is also invalid if 1. the stack is empty; or 2. the top stack item is negative; or 3. the top stack item is greater than or equal to 500000000 while the transaction's nLockTime field is less than 500000000, or vice versa; or 4. the input's nSequence field is equal to 0xffffffff. The precise semantics are described in BIP 0065. |
OP_CHECKSEQUENCEVERIFY (previously OP_NOP3) | 178 | 0xb2 | x | x / fail | Marks transaction as invalid if the relative lock time of the input (enforced by BIP 0068 with nSequence) is not equal to or longer than the value of the top stack item. The precise semantics are described in BIP 0112. |
Reserved words
Any opcode not assigned is also reserved. Using an unassigned opcode makes the transaction invalid.
Word | Opcode | Hex | When used... |
---|---|---|---|
OP_RESERVED | 80 | 0x50 | Transaction is invalid unless occuring in an unexecuted OP_IF branch |
OP_VER | 98 | 0x62 | Transaction is invalid unless occuring in an unexecuted OP_IF branch |
OP_VERIF | 101 | 0x65 | Transaction is invalid even when occuring in an unexecuted OP_IF branch |
OP_VERNOTIF | 102 | 0x66 | Transaction is invalid even when occuring in an unexecuted OP_IF branch |
OP_RESERVED1 | 137 | 0x89 | Transaction is invalid unless occuring in an unexecuted OP_IF branch |
OP_RESERVED2 | 138 | 0x8a | Transaction is invalid unless occuring in an unexecuted OP_IF branch |
OP_NOP1, OP_NOP4-OP_NOP10 | 176, 179-185 | 0xb0, 0xb3-0xb9 | The word is ignored. Does not mark transaction as invalid. |
Script examples
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. These examples include the “OP_” prefix, but it is permissible to omit it. Thus “<pubkey1> <pubkey2> OP_2 OP_CHECKMULTISIG” may be abbreviated to “<pubkey1> <pubkey2> 2 CHECKMULTISIG”. 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.
Standard Transaction to Bitcoin address (pay-to-pubkey-hash)
scriptPubKey: OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG scriptSig: <sig> <pubKey>
To demonstrate how scripts look on the wire, here is a raw scriptPubKey:
76 A9 14 OP_DUP OP_HASH160 Bytes to push 89 AB CD EF AB BA AB BA AB BA AB BA AB BA AB BA AB BA AB BA 88 AC Data to push OP_EQUALVERIFY OP_CHECKSIG
Note: scriptSig is in the input of the spending transaction and scriptPubKey is in the output of the previously unspent i.e. "available" transaction.
Here is how each word is processed:
Stack | Script | Description |
---|---|---|
Empty. | <sig> <pubKey> OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | scriptSig and scriptPubKey are combined. |
<sig> <pubKey> | OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | Constants are added to the stack. |
<sig> <pubKey> <pubKey> | OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | Top stack item is duplicated. |
<sig> <pubKey> <pubHashA> | <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | Top stack item is hashed. |
<sig> <pubKey> <pubHashA> <pubKeyHash> | OP_EQUALVERIFY OP_CHECKSIG | Constant added. |
<sig> <pubKey> | OP_CHECKSIG | Equality is checked between the top two stack items. |
true | Empty. | Signature is checked for top two stack items. |
Obsolete pay-to-pubkey transaction
OP_CHECKSIG is used directly without first hashing the public key. This was used by early versions of Bitcoin where people paid directly to IP addresses, before Bitcoin addresses were introduced. scriptPubKeys of this transaction form are still recognized as payments to user by Bitcoin Core. 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.
scriptPubKey: <pubKey> OP_CHECKSIG scriptSig: <sig>
Checking process:
Stack | Script | Description |
---|---|---|
Empty. | <sig> <pubKey> OP_CHECKSIG | scriptSig and scriptPubKey are combined. |
<sig> <pubKey> | OP_CHECKSIG | Constants are added to the stack. |
true | Empty. | Signature is checked for top two stack items. |
Provably Unspendable/Prunable Outputs
The standard way to mark a transaction as provably unspendable is with a scriptPubKey of the following form:
scriptPubKey: OP_RETURN {zero or more ops}
OP_RETURN immediately marks the script as invalid, guaranteeing that no scriptSig exists that could possibly spend that output. Thus the output can be immediately pruned from the UTXO set even if it has not been spent. eb31ca1a4cbd97c2770983164d7560d2d03276ae1aee26f12d7c2c6424252f29 is an example: it has a single output of zero value, thus giving the full 0.125BTC fee to the miner who mined the transaction without adding an entry to the UTXO set. You can also use OP_RETURN to add data to a transaction without the data ever appearing in the UTXO set, as seen in 1a2e22a717d626fc5db363582007c46924ae6b28319f07cb1b907776bd8293fc; P2Pool does this with the share chain hash txout in the coinbase of blocks it creates.
Freezing funds until a time in the future
Using OP_CHECKLOCKTIMEVERIFY it is possible to make funds provably unspendable until a certain point in the future.
scriptPubKey: <expiry time> OP_CHECKLOCKTIMEVERIFY OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG scriptSig: <sig> <pubKey>
Stack | Script | Description |
---|---|---|
Empty. | <sig> <pubKey> <expiry time> OP_CHECKLOCKTIMEVERIFY OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | scriptSig and scriptPubKey are combined. |
<sig> <pubKey> <expiry time> | OP_CHECKLOCKTIMEVERIFY OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | Constants are added to the stack. |
<sig> <pubKey> <expiry time> | OP_DROP OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | Top stack item is checked against the current time or block height. |
<sig> <pubKey> | OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | Top stack item is removed. |
<sig> <pubKey> <pubKey> | OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | Top stack item is duplicated. |
<sig> <pubKey> <pubHashA> | <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG | Top stack item is hashed. |
<sig> <pubKey> <pubHashA> <pubKeyHash> | OP_EQUALVERIFY OP_CHECKSIG | Constant added. |
<sig> <pubKey> | OP_CHECKSIG | Equality is checked between the top two stack items. |
true | Empty. | Signature is checked for top two stack items. |
Transaction puzzle
Transaction a4bfa8ab6435ae5f25dae9d89e4eb67dfa94283ca751f393c1ddc5a837bbc31b is an interesting puzzle.
scriptPubKey: OP_HASH256 6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000 OP_EQUAL scriptSig:
To spend the transaction you need to come up with some data such that hashing the data twice results in the given hash.
Stack | Script | Description |
---|---|---|
Empty. | OP_HASH256 <given_hash> OP_EQUAL | |
OP_HASH256 <given_hash> OP_EQUAL | scriptSig added to the stack. | |
<data_hash> | <given_hash> OP_EQUAL | The data is hashed. |
<data_hash> <given_hash> | OP_EQUAL | The given hash is pushed to the stack. |
true | Empty. | The hashes are compared, leaving true on the stack. |
This transaction was successfully spent by 09f691b2263260e71f363d1db51ff3100d285956a40cc0e4f8c8c2c4a80559b1. 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-256. 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.
Incentivized finding of hash collisions
In 2013 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.
For example the SHA1 script:
scriptPubKey: OP_2DUP OP_EQUAL OP_NOT OP_VERIFY OP_SHA1 OP_SWAP OP_SHA1 OP_EQUAL scriptSig: <preimage1> <preimage2>
See the bitcointalk thread [3] and reddit thread[4] for more details.
In February 2017 the SHA1 bounty worth 2.48 bitcoins was claimed.
See Also
External Links
- BitIDE - BitIDE: A web based Bitcoin Script IDE with built in debugger, meta-scripting, virtual op-codes, and local testnet.
- [2] - Miniscript: a language for writing (a subset of) Bitcoin Scripts in a structured way, enabling analysis, composition, generic signing and more.
- Bitcoin IDE – Bitcoin Script for dummies
- Bitcoin Debug Script Execution – web tool which executes a script opcode-by-opcode
- Script Playground — convert Script to JavaScript
- BitAuth IDE — an Integrated Development Environment for Bitcoin Authentication
(cf. "Online Bitcoin Script simulator or debugger?")
References
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