How to write OP_CHECKMULTISIG for the following 1-of-2 multisig P2SH script

From what I understand from your question (correct me if I'm wrong), you want to have a script that in the OP_IF part pays to 1-of-2 public keys. You could try the below script:

OP_IF
  OP_SHA256
  OP_DATA (0x20)
  <hash of secret>
  OP_EQUALVERIFY
  OP_1 
  OP_DATA (0x21) 
  <pubKey of swap1>
  OP_DATA (0x21)
  <pubkey of swap2>
  OP_2
  OP_CHECKMULTISIG
OP_ELSE
  OP_DATA (size of relative_locktime)
  <relative locktime>
  OP_CHECKSEQUENCEVERIFY
  OP_DROP
  OP_DATA (0x21)
  <pubKey of refund>
  OP_CHECKSIG
OP_ENDIF

You could spend this script with: <0> <sig1> <secret> 1

Ugam Kamat

Posted 2019-06-11T06:24:04.163

Reputation: 5 180

Yes @Ugam Kamat you are actually right. I have edit my question please see it again..Actually the complication which i am facing is, how to provide these two public keys . Is it the right way? ``` var add=[recipientPublicKey,exchangePublicKey] Whereas Inside compile Buffer.from(add, "hex"), this.app.env.bitcoin.opcodes.OP_2, this.app.env.bitcoin.opcodes.CHECKMULTISIG, Is it correct? – Aqeel – 2019-06-11T11:11:17.123

@Aqeel You need to use a OP_DATA opcode between them to indicate the bytes of data to push to stack. For example, to push hash_of_secret to stack you need to tell the program to push the next 32 bytes which is the reason we need 0x20 preceding that as shown in my edited answer – Ugam Kamat – 2019-06-11T11:47:13.203

Thanks for reply. But Opcode you listed "OP_DATA" is not a valid opcode. I have printed the list of opcodes but that opcode is not in the list and therefor creating error – Aqeel – 2019-06-11T12:41:30.410

@Aqeel It's not exactly an opcode but a parameter that helps you indicate to the software how much data you want to push on the stack. For example, if you see my script i used 0x20 before hash of secret. It indicates to the software to push the next 32 bytes (ox20 in hex) on the stack. Before the pubkey I used 0x21 to indicate pushing the next 33 bytes on the stack (assuming you are using compressed pub keys) – Ugam Kamat – 2019-06-11T13:17:24.033

Can you provide me any helping material for 1-of-2 p2sh multisig script, which may helps me in writing script in desired format. – Aqeel – 2019-06-12T06:08:50.057

@Aqeel I don't think there is one specific to 1-of-2 p2sh multisig. Even if it is out there I'm oblivious to it – Ugam Kamat – 2019-06-12T06:17:01.757

actually the thing which i want to see is how can i pass list of pubkeys to apply OP_CHECKMULTISIG in desired code format... The ref repo is: https://github.com/swaponline/swap.core/blob/97d1d5b6afffee97869302443924bef79ce42763/src/swap.swaps/BtcSwap.js#L181 I am changing this piece of script to 1-of-2 p2sh multisig. Any guidance for me after seeing this script form above reference link?

– Aqeel – 2019-06-12T06:35:53.523

@Aqeel I haven't gone through the code in detail, but maybe you can repeat Buffer.from(recipientPublicKey, 'hex'), twice with different public key and then instead of this.app.env.bitcoin.opcodes.OP_CHECKSIG use this.app.env.bitcoin.opcodes.OP_CHECKMULTISIG – Ugam Kamat – 2019-06-12T07:29:10.230

How to write OP_CHECKMULTISIG for the following 1-of-2 multisig P2SH script

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