20 - Dash Opcode Updates#

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

Abstract#

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.

Motivation#

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.

Specification#

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

OP_CAT#

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:

OP_SPLIT#

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 0x001122

  • 0x001122 1 OP_SPLIT → 0x00 0x1122

  • 0x001122 2 OP_SPLIT → 0x0011 0x22

  • 0x001122 3 OP_SPLIT → 0x001122 OP_0

References:

OP_NUM2BIN#

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 → 0x00000002

  • 0x85 4 OP_NUM2BIN → 0x80000005

References:

OP_BIN2NUM#

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 → 0x02

  • 0x800005 OP_BIN2NUM → 0x85

References:

OP_AND#

Opcode (decimal): 132
Opcode (hex): 0x84

Boolean and between each bit in the operands.

x1 x2 OP_AND → out

References:

OP_OR#

Opcode (decimal): 133
Opcode (hex): 0x85

Boolean or between each bit in the operands.

x1 x2 OP_OR → out

References:

OP_XOR#

Opcode (decimal): 134
Opcode (hex): 0x86

Boolean xor between each bit in the operands.

x1 x2 OP_XOR → out

References:

OP_DIV#

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:

OP_MOD#

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:

OP_CHECKDATASIG#

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:

OP_CHECKDATASIGVERIFY#

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:

Compatibility#

This change will be a hard-fork to the protocol and older software has to be updated to continue to operate.

References#