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Could someone explain what the commands i have in bold do? if possible. Thank you.

Transaction URL www.blockchain.com/btc/tx

Input Scripts- ScriptSig: PUSHDATA(71)[3044022069f0c9da12ce7b002c68d25e4445191b149627987367fdec4e4b80e442379f3902202109994c46d8c6afd8e94542d07fa8a07da234f7537c4a1d639d2dcdd32f9c5b01] PUSHDATA(33)[03c26e5ff8c75d6272b2d9cd3a882c20315d440251deb79873b75b690d0b71f4cf]

Output Scripts- DUP HASH160 PUSHDATA(20)[264cf7a09b68a436bafc4d7281743d7f1c721ded] EQUALVERIFY CHECKSIG HASH160 PUSHDATA(20)[72cf56ba8b7312ae658debf033d88e4370b9a8f5] EQUAL

  • Note that you have two separate output scripts merged together in your question. There are two outputs and therefore two output scripts. – Dmitry Laptev Mar 12 at 22:00
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There is a nice introduction to script and already another answer explaining what these specific commands do, but I will try to explain what these scripts actually do.

They implement a very standard bitcoin transaction called pay-to-pubkey-hash transaction.

The idea is roughly the following. Let's call this transaction A. To spend the output of transaction A, another transaction will be created and broadcasted, let's call it B. In order to verify the validity of transaction B, one should:

  1. combine the input script of B with the output script of A,
  2. execute the combined script and verify that it returns True.

In this type of transactions, transaction B should provide an input script that puts two elements to the stack: the signature sig of the transaction and a corresponding public key pubKey. Note how the input script of transaction A is also doing exactly that.

Then the output script of transaction A will do the following (in your question you actually provide two output scripts merged together, because there are two outputs, I will focus on the first one):

  1. Duplicate pubKey on the stack;
  2. Hash one pubKey from the stack and verify that it is equal to 264cf7a09b68a436bafc4d7281743d7f1c721ded
  3. Take sig and the remaining pubKey from the stack and verify the validity of the signature.
  • 1st thank you. 2nd I think i understand what your saying. So basically for the balance to be spendable, another transaction has to take place to verify it spendable? – gReigns Mar 14 at 19:59
  • @gReigns roughly, yes, depending on what you mean by “spendable”. Transaction A dictates the conditions under which the balance (or rather UTXO is a better term) can be spend. But until transaction B appears and spends these outputs by providing the right signature, no one really knows if these conditions are possible to meet. – Dmitry Laptev Mar 16 at 10:14
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  • PUSHDATA(71): Pushes the next 71 bytes onto the top of stack
  • PUSHDATA(33): Pushes the next 33 bytes onto the top of stack
  • DUP: Pushes a duplicate of the top stack item onto the top of the stack
  • HASH160: Pop the top stack item off of the stack, hash it using SHA256 then that hash with RIPEMD160, and push the resulting hash to the top of the stack
  • PUSHDATA(20): Push the next 20 bytes onto the top of the stack
  • EQUALVERIFY: Check that the top two stack items are equal. If they are, do nothing. If they are not, immediately fail execution
  • CHECKSIG:Pop the top stack item and interpret it as a public key. Pop the next stack item and interpret it as a signature. Check that the signature verifies to that public key when the message that is signed is a modified version of the transaction containing the signature. If the signature is valid, push OP_TRUE to the top of the stack. If it is false, push OP_FALSE to the top of the stack.

A full description of all script opcodes and their actual byte values can be found on the Bitcoin wiki.

  • Can't believe that this was not a duplicate. I will add a link to a video in which I dissect a pay2pkh tx: youtu.be/1n4g3eYX1UI that should help to understand how these op codes work – Rene Pickhardt Mar 12 at 21:50

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