Ah okay now I understand.
But I think I am missing this two point:
1)How do the other nodes validate the transaction between A and B?
2)Why do we have the OP_EQUALVERIFY? It permits to check the two pubkeys at the top of the stack, but why do we need to check them?

Thanks,

Thanks, the thing that was confusing me was that you were referring to the Alice's previous transaction.
Having A->B transaction only B can spend, but every nodes of the network have to validate the transaction.
A and B execute this script <Sig> <PubKey> OP_DUP OP_HASH160 <PubkeyHash> OP_EQUALVERIFY OP_CHECKSIG  to validate the transaction and so permitting B to spend. What do other nodes do to validate A->B transaction?

According to this: https://bitcoin.org/en/transactions-guide#introduction


And

Thanks for answering,

I don't understand why you're talking about Alice's private key and scriptSig if the transaction is between Alice and Bob, I mean in every guide I read there is a transaction between Alice and Bob and Alice has the scritpPubKey and Bob has the scriptSig.
I think you're saying about that before Alice can send bitcoin to Bob, she has to receive bitcoin from another transaction for example a transaction Cindy-Alice and so Alice has the private key to spend UTXO, are you referring to this?
I read the article and I don't understand this "their software will use the private key of an unspent output (a 'bitcoin') to cryptographically sign the transaction. This signature proves ownership of the unspent output, and authorizes movement of the coins."
It says that the transaction is signed by utxo, but the sign is in the scriptSig so in the input..

And the other thing I don't understand is this:
A transaction between A (sender) and B (receiver), so A and B have the scripts and using op_checksig the transaction is validated. In which way the other nodes validate the transaction? I mean then B broadcasts the transaction and the transaction is received by C and now B and C have the scripts. I don't know if I explained me clearly.

Thanks,

I don't understand, if the transaction is p2pkh from Alice to Bob and they have scripts to verify the transaction, how can other nodes verify the transaction? I mean the other nodes don't have the scriptPubKey and the scriptSig referring to Alice and Bob.

And referring to this
The PoW algorithm validates a block made up of transactions, while the scripts validate transactions, I mean are they two different and separate things?

Good evening, I have some doubts about transactions validation. Always referring to this link https://bitcoin.org/en/transactions-guide#introduction

If the transaction is between Alice and Bob with Alice as sender and Bob as receiver, after Alice checks the sign with OP_CHECKSIG operation, why, as stated above, the transaction has to be validated by every node of the network?

Another thing, after a block has a certain number of transaction the block is validated and inserted in the blockchain with the PoW algorithm?

Thanks,

The meaning of digital signature in Bitcoin can be summarize as "a digital signature can be used to unlock outputs, because it shows that we know the private key of an address"? Where the address refers to the receiver.

Following this guide https://bitcoin.org/en/transactions-guide#introduction I don't understand this:

I don't understand in particular these points:
2) Why do we need to sign previous output's pubkey script?
3) and 4) if this is the unlocking script  why do we need to sign things for next transactions?

Thanks,

Thanks for clarification. But another question, is p2pkh a smart contract?

Hi everyone, after reading about Transaction at this link https://bitcoin.org/en/transactions-guide#introduction I have some doubts.
At the end Avoiding Key Reuse there is this:

I don't understand the last part about using public key only twice, in particular I mean the public key isn't only used by the receiver to say the address towards which sending the payment? Why does the article say that the public key is used also by the sender, so by the spender?

Thanks,