Opcodes

A detailed introduction to Bitcoin opcodes.

Bitcoin uses a script system for transactions. Similar to the Forth language, Bitcoin's script system is simple, stack-based, and processed from left to right.

Scripts are essentially a series of instructions recorded in each transaction, describing how the next person wanting to spend the transferred Bitcoin can gain access. A typical script that transfers Bitcoin to a target Bitcoin address restricts future spending with two conditions: the spender must provide:

1. A public key that, when hashed, matches the target embedded in the script.
2. A signature proving ownership of the private key corresponding to the provided public key.

MVC has improved and expanded Bitcoin's script system to make it more powerful and flexible.

List of Opcodes

For a list of opcodes, refer to: https://en.bitcoin.it/wiki/Script

Constants

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) after the OP_RETURN provided the total scriptPubKey length is at most 83 bytes.

Stack Operations

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.

String Operations

If any opcode marked as disabled is present in the script, the script 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 the string. Disabled. | | OP_RIGHT | 129 | 0x81 | in size | out | Keeps only characters right of the specified point in the string. Disabled. | | OP_SIZE | 130 | 0x82 | in | in size | Pushes the string length of the top stack item (without popping it). |

Bitwise Logic Operations

If any opcode marked as disabled is present in the script, the script must abort and fail.

Word	Opcode	Hex	Input	Output	Description
OP_INVERT	131	0x83	in	out	Flips all the bits in the input. Disabled.
OP_AND	132	0x84	x1 x2	out	Boolean AND between each bit of the inputs. Disabled.
OP_OR	133	0x85	x1 x2	out	Boolean OR between each bit of the inputs. Disabled.
OP_XOR	134	0x86	x1 x2	out	Boolean XOR between each bit of 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 Operations

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	a b	out	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.

Cryptographic Operations

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	None	None	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 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