For instance, I need to create a transaction, T1, that makes use of an output from a earlier transaction, T0. This output is locked by a P2PKH script and desires the right scriptSig.
To get the right scriptSig, I would like a signature and a public key however what’s the message that has been signed to create the signature? Is it the transaction knowledge from T0?
If the outputs of T1 are locked with P2PKH, once I need to spend these outputs, is the signature the transaction knowledge of T1 signed?