How much of a PDA is under the control of its owner program? For example, could the program block the account from signing certain instructions on transactions? Or could the program add a fee to every transaction a PDA signs? Whats the limit of control over PDAs and how can you access all features of them on Anchor
3 Answers
a PDA is limited to how much the program offers in controllability.
To elaborate. Let's say your program has a single instruction initialize that initializes a pda account. In that case, your program cannot change the PDA after it's initialized.
You add an update instruction that updates the PDA data to a certain way. This will offer you the ability to use that instruction to update it. But only in that certain way.
This is great for security because you don't have to worry that a pda might be initialized in a malicious way or it has unvalid data. The pda will only follow the rules of the program. It cannot be updated outside of the program.
PDA can store DATA and also sign for CPI(Cross program Invocations) for example you have an escrow and you have created a tokenAccount whose authority is a PDA then only the PDA can control the transfer of tokens from that TokenAccount.
A program only has explicit signing authority over its PDAs, so its control is limited to everything that it can sign.
After that, if your program creates an account at a PDA, then it can control that account as much as any other account that it owns.
Feel free to read through the official documentation on program-derived addresses at https://docs.solana.com/developing/programming-model/calling-between-programs#program-derived-addresses and on account ownership at https://docs.solana.com/developing/programming-model/accounts#ownership-and-assignment-to-programs
