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I am working on a little script to breakdown the data inside coinbase transactions. This is largely to improve my understanding of legacy and SegWit transactions (Given coinbase transactions have less data than for example a multisig TX, it is easier for me to work through).

One thing I've noticed about these transactions is differences in the output scripts. The Bitcoin RPC API works pretty well in decoding them, though I would like to know how to do it without an external tool. I am aware that there are different types such as P2PKH, P2SH, and P2PK. However, what I do not know is how to differentiate them only given the raw hexadecimal representation.

For example this transaction has two output scripts:

76A91494155788E7233D7BEA9AA29FEB2ED37BC878C40B88AC

and

6A24AA21A9ED7387872912D999B657F4146043675D84B9BBCF66AD5DEC8BCC14117E4FB6999E

The RPC API tells me the first one has the type pubkeyhash with a P2SH value of 3EstC3Hhe8zvNGP73oX9oDvo36sNCygjJi

The second output script appears to be random data which cannot be decoded. (I've also seen many coinbase transactions have one readable output and one or more output that cannot be decoded).

Another example, The genesis block coinbase transaction decoded by the RPC API has the type pubkey with this script:

4104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac

Question: How can I take this output script and determine the type of transaction and the assembly (OP script code) of it without external APIs?

Thank you!

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  • As I was writing this I stumbled upon this image which implies that the scriptPubKeys follow a standardized format, can someone confirm it is accurate? Thanks again!
    – Mason Ticehurst
    Commented Sep 9, 2018 at 23:34

2 Answers 2

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thx for linking one of my older pics from 2016 :-) meanwhile things had changed, especially the multisig was not clear enough. I attach an updated version here. I didn't have the time to put newest SegWit related things into the pic though... Still happy to see other opinions ...

output script

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  • Thanks man! I ended up figuring out most of the information I needed once I reviewed your picture. One other question I figured I'd ask. I know with the adoption of segregated witness there has been some degree of backwards compatibility with P2SH. Though, I have also heard people mention P2SH-P2WSH, P2WSH, P2WPKH, and P2SH-P2WPKH. Would you happen to know what differences there are in these versions, if any? Or perhaps a thread that might share the details? Regardless, thanks for this! PS: I'd love to upvote this too, but I don't have enough reputation yet :(
    – Mason Ticehurst
    Commented Sep 10, 2018 at 17:14
  • I haven't seen any "prepared" stuff for easy usage, so my reference is currently here: en.bitcoinwiki.org/wiki/Segregated_Witness - with the links at the bottom to BIPs and the Wallet Development Guide.
    – pebwindkraft
    Commented Sep 10, 2018 at 18:07
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Bitcoin core just rolled out descriptor wallet implementation (PR here). Descriptors are modeled as functions. They take input a public key, and return the corresponding scriptPubKey,describing its spending conditions in engineer-readable format. For example, sh(wpkh(03fff97bd5755eeea420453a14355235d382f6472f8568a18b2f057a1460297556)) describes a P2SH-P2WPKH output with the specified public key.

You can refer to this doc for more details. achow101 also gave a great talk (15 min) to explain this idea in details.

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