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As explained in

https://en.bitcoin.it/wiki/Script

there are many types of scriptPubKey and scriptSig like:

<sig> <pubKey>
<sig> <pubKey> <pubKey> 
<sig> <pubKey> <pubHashA> 
<sig> <pubKey> <pubHashA> <pubKeyHash>
...

how can we detect type of ScriptSig and separate each part? In other words is there a length variable or something like that to parse each part separately?

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Really, the only way to detect the type is to parse it as a program.

All scripts Bitcoin are written in the Bitcoin Script language. Much like any other programming language, certain symbols have special meaning, and correspond to specific op codes, which appear in the raw hex form. You can find a list of op codes on the Bitcoin Wiki: https://en.bitcoin.it/wiki/Script#Opcodes

The standardized scripts, which are usually what we see presented as addresses, are really just specific snippets of Bitcoin Script programs. For example, a P2PKH "address" is really just half a program in the form of:

OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG

When combined with the remaining half of the program, which is provided as the ScriptSig when spending the coins, you get a complete program which can be evaluated.

To determine the script type, you really just need to parse the program (or partial program, in the event of an output) and see if it matches a known, standardized type.

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  • I mean how I can parse a scriptsig which is like this : scriptSig: <sig> <pubKey> in other words, i want to find it's public key to generate related address.
    – Saeed
    Jun 16, 2019 at 8:48
  • A script sig is just a bitcoin script fragment - even simpler, they are restricted to only use OP_PUSH, so to read the signature and public key, you read the first byte for the push length, then read that many bytes as data, then read the next byte, and read that many bytes as data again - The first chunk of data is a DER encoded signature, and the second chunk is the public key
    – Raghav Sood
    Jun 16, 2019 at 9:44
  • Naturally, the above only works for P2PKH/P2PK addresses - P2SH and segwit addresses will require more effort
    – Raghav Sood
    Jun 16, 2019 at 9:45
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    Because they also look at the output being spent. That's how validation works. That's what you need to do to get any insight in what's going on. Also, addresses are not relevant for balance validation: the question is simply whether or not the output being spent was previously spent or not already, and if not, what value it had. Addresses are a human-level abstraction into the authentication mechanism, but don't exist at all at the protocol level. In particular, there is no such thing as an address balance. Just UTXOs.
    – Pieter Wuille
    Jun 17, 2019 at 5:07
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    As I advised you elsewhere, stop looking at protocol dumps and trying to match that information up with block explorers. If you want to understand what's going on, read how transactions and other things in the protocol work.
    – Pieter Wuille
    Jun 17, 2019 at 5:10

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