Why this witness doesn't seems to contain a public key?

Question

I am learning how transactions are coded in the blockchain, so I used a python script to compute bitcoin address from public key. This works with the public key: 03416fe9ba17be8fe3f88011923135e83c6a0666fcb575de6ab337c7d6c8f41a5f

within the sigscript if this transaction: https://www.blockchain.com/btc/tx/56beef8afe5a4b5b41225211e62c3e7bce5747c4c8dcdd982173e8496687794b I correctly get the corresponding address:

15nrxBDLts1tEbowH1dLm5z84RVas7USmP

I tried with the same python code to check where is the public key of the first input of this transaction: https://www.blockchain.com/btc/tx/01e7c525a5759cde1d04d2e9a363424053ace3ff1d2dde9cd1b368493254bd0d

I tried to check if I get the address of this input: 34xp4vRoCGJym3xR7yCVPFHoCNxv4Twseo Unfortunately, I didn't manage to end with this address when I use the second field of the witness of this input, which should be the public key of the address I am trying to get (the one starting with 34xp): 02a720e54e39b28434a4c55462718b4584db973331a834141b8cad7e52c317f695

SHA256+RIPEMD160+b58encode on this data doesn't correspond to the address above (the one starting with 34xp), and I didn't figured out why, and where is the public key of this address in this transaction input. Could anyone please give me a clue about it?

Answer 1

I found my answer in this post: Find sender's public key in SegWit Transaction

Without witness:

address = base58check( 0x00 + hash160(publicKey) )

With witness:

address = base58check( 0x05 + hash160( 0x00 + 0x14 + hash160(publicKey) ) )

With:

• "+" operator is concatenation
• hash160() is SHA256 + RIPEMD160
• publicKey is the second element of the witness (the one I correctly identified in my question above), or the second element of sigscript if no witness

Well note that this is not a global rule, but the rule for the transactions I mentioned.