How to create a transaction with a custom script?

Question

Is there a step-by-step tutorial or any documentation covering how to create a transaction that is not a standard OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG?

It seems very odd that there is absolutely no documentation or information covering how to create a transaction like this, when it is one of Bitcoin's greatest advantages.

Maybe a link to some open-source software which creates custom script transactions would be helpful. I don't know of any that exist off hand though.

Answer 1

I would suggest using Python to accomplish this. pybitcointools have what you need to be able to deserialize a hex transaction to JSON, and manipulate that and then serialize again to be able to sign and broadcast via support for blockchain.info.

This example will rebuild the standard script from the ground up:

>>> opdup = 0x76
>>> ophash160 = 0xA9
>>> push20 = 0x14
>>> opeqver = 0x88
>>> opchecksig = 0xAC
>>> pubkeyhash = 0x2dbde30815faee5bf221d6688ebad7e12f7b2b1a

We are going to append hex values by moving them bitwise.

• OP_DUP OP_HASH160 2dbde30815faee5bf221d6688ebad7e12f7b2b1a OP_EQUALVERIFY OP_CHECKSIG
• This is the hex we want 76a9142dbde30815faee5bf221d6688ebad7e12f7b2b1a88ac

This is one way of doing it

>>> quickfix = 0xff
>>> asm = quickfix
>>> asm = asm << 8 | opdup
>>> asm = asm << 8 | ophash160
>>> asm = asm << 8 | push20
>>> asm = asm << 8*20 | pubkeyhash
>>> asm = asm << 8 | opeqver
>>> asm = asm << 8 | opchecksig

Ant then to check if its the same:

>>> almost = hex(asm)
>>> ready = almost.partition("0xff")[2]
>>> print(ready)

Hope this is what you are after :-)

Answer 2

ABSOLUTELY Go!

import(
    "github.com/btcsuite/btcd/txscript"
    "github.com/btcsuite/btcd/wire"
)

tx := wire.NewMsgTx(2)
tx.AddTxOut(wire.NewTxOut(int64(*outputvalueFlag*1e8), script()))

func script() ([]byte) {
    script := txscript.NewScriptBuilder()
    script.AddInt64(1)
    script.AddData(bytes[0:65])
    script.AddInt64(1)
    script.AddOp(txscript.OP_CHECKMULTISIG)
    return script.Script()
}
...