DIP: 0020 Title: Dash Opcode Updates Author: Mart Mangus Comments: https://github.com/Dash-Dev-EE/DIP-draft/issues Status: Draft Layer: Consensus (hard fork) Created: 2020-06-01 License: MIT License
This DIP describes reactivation of several disabled opcodes (OP_CAT, OP_AND, OP_OR, OP_XOR, OP_DIV, OP_MOD) and activation of several new opcodes (OP_SPLIT, OP_BIN2NUM, OP_NUM2BIN, OP_CHECKDATASIG and OP_CHECKDATASIGVERIFY) to expand the use of the Dash scripting system.
Several opcodes were disabled in the Bitcoin scripting system due to the discovery of a series of bugs in the early days of Bitcoin. The functionality of these opcodes was re-examined by Bitcoin Cash developers few years ago. Many of the disabled opcodes have been enabled and several of them re-designed to replace the original ones. In addition, several new opcodes have been written and implemented to further improve the Bitcoin scripting system in Bitcoin Cash. Implementing these opcodes into Dash is necessary for broadening the functionality of the system and enabling developers to build new solutions, which in turn would expand the use of Dash.
| Word | OpCode | Hex | Input | Output | Description |
|---|---|---|---|---|---|
| OP_CAT | 126 | 0x7e | x1 x2 | out | Concatenates two byte arrays |
| OP_SPLIT | 127 | 0x7f | x n | x1 x2 | Split byte array x at position n |
| OP_NUM2BIN | 128 | 0x80 | a b | out | Convert numeric a into byte array of length b |
| OP_BIN2NUM | 129 | 0x81 | x | out | Convert byte array x into numeric |
| OP_AND | 132 | 0x84 | x1 x2 | out | Boolean AND between each bit of the inputs |
| OP_OR | 133 | 0x85 | x1 x2 | out | Boolean OR between each bit of the inputs |
| OP_XOR | 134 | 0x86 | x1 x2 | out | Boolean EXCLUSIVE OR between each bit of the inputs |
| OP_DIV | 150 | 0x96 | a b | out | a is divided by b |
| OP_MOD | 151 | 0x97 | a b | out | return the remainder after a is divided by b |
| OP_CHECKDATASIG | 186 | 0xba | sig msg pk | out | If signature sig is valid, output to the stack |
| OP_CHECKDATASIGVERIFY | 187 | 0xbb | sig msg pk | - | If signature sig is valid, false will cause the script to fail |
Opcode (decimal): 126
Opcode (hex): 0x7e
OP_CAT takes two byte arrays from the stack, concatenates them and pushes the result back to the stack.
x1 x2 OP_CAT → out
Example:
0x11 0x2233 OP_CAT → 0x112233
References:
Opcode (decimal): 127
Opcode (hex): 0x7f
OP_SPLIT is the inverse of OP_CAT and a replacement operation for disabled opcodes OP_SUBSTR, OP_LEFT and OP_RIGHT.
OP_SPLIT takes a byte array, splits it at the position n (a number) and returns two byte arrays.
x n OP_SPLIT → x1 x2
Examples:
0x001122 0 OP_SPLIT → OP_0 0x0011220x001122 1 OP_SPLIT → 0x00 0x11220x001122 2 OP_SPLIT → 0x0011 0x220x001122 3 OP_SPLIT → 0x001122 OP_0
References:
Opcode (decimal): 128
Opcode (hex): 0x80
OP_NUM2BIN converts numeric value n to a byte array of length m.
n m OP_NUM2BIN → x
Examples:
0x02 4 OP_NUM2BIN → 0x000000020x85 4 OP_NUM2BIN → 0x80000005
References:
Opcode (decimal): 129
Opcode (hex): 0x81
OP_BIN2NUM converts byte array value x into a numeric value.
x1 OP_BIN2NUM → n
if x1 is any form of zero, including negative zero, then OP_0 must be the result.
Examples:
0x0000000002 OP_BIN2NUM → 0x020x800005 OP_BIN2NUM → 0x85
References:
Opcode (decimal): 132
Opcode (hex): 0x84
Boolean and between each bit in the operands.
x1 x2 OP_AND → out
References:
Opcode (decimal): 133
Opcode (hex): 0x85
Boolean or between each bit in the operands.
x1 x2 OP_OR → out
References:
Opcode (decimal): 134
Opcode (hex): 0x86
Boolean xor between each bit in the operands.
x1 x2 OP_XOR → out
References:
Opcode (decimal): 150
Opcode (hex): 0x96
Return the integer quotient of a and b. If the result would be a non-integer it is rounded towards zero. a and b are interpreted as numeric values.
a b OP_DIV → out
References:
Opcode (decimal): 151
Opcode (hex): 0x97
Returns the remainder after dividing a by b. The output will be represented using the least number of bytes required. a and b are interpreted as numeric values.
a b OP_MOD → out
References:
Opcode (decimal): 186
Opcode (hex): 0xba
OP_CHECKDATASIG checks whether a signature is valid with respect to a message and a public key. It allows Script to validate arbitrary messages from outside the blockchain.
sig msg pubKey OP_CHECKDATASIG → out
If the stack is well formed, then OP_CHECKDATASIG pops the top three elements [sig, msg, pubKey] from the stack and pushes true onto the stack if sig is valid with respect to the raw single-SHA256 hash of msg and pubKey using the secp256k1 elliptic curve. Otherwise, it pops three elements and pushes false onto the stack in the case that sig is the empty string and fails in all other cases.
References:
Opcode (decimal): 187
Opcode (hex): 0xbb
OP_CHECKDATASIGVERIFY is equivalent to OP_CHECKDATASIG followed by OP_VERIFY. It leaves nothing on the stack and will cause the script to fail immediately if the signature check does not pass.
sig msg pubKey OP_CHECKDATASIGVERIFY
References:
This change will be a hard-fork to the protocol and older software has to be updated to continue to operate.
- Bitcoin Cash specification of restored disabled opcodes: https://github.com/bitcoincashorg/bitcoincash.org/blob/master/spec/may-2018-reenabled-opcodes.md
- Bitcoin Cash specification of OP_CHECKDATASIG and OP_CHECKDATASIGVERIFY: https://github.com/bitcoincashorg/bitcoincash.org/blob/master/spec/op_checkdatasig.md
- Bitcoin Cash OP_CHECKDATASIG and OP_CHECKDATASIGVERIFY implementation:
- Bitcoin Cash OP_CAT implementation: https://reviews.bitcoinabc.org/D1097
- Bitcoin Cash OP_SPLIT implementation: https://reviews.bitcoinabc.org/D1099
- Bitcoin Cash OP_BIN2NUM implementation: https://reviews.bitcoinabc.org/D1101
- Bitcoin Cash OP_NUM2BIN implementation: https://reviews.bitcoinabc.org/D1103
- Bitcoin Cash OP_AND, OP_OR and OP_XOR implementation: https://reviews.bitcoinabc.org/D1211
- Bitcoin Cash OP_DIV and OP_MOD implementation: https://reviews.bitcoinabc.org/D1212
This document is licensed under the MIT License.