Why there are signature and public key pair on blocks when transaction verifying is over

Question

I'm student studying about bitcoin and blockchain. I want to know why all blocks have signature and key pair after the transaction is over.

Why I ask this, I'm studying post quantum cryptography (PQC) and almost PQC have very large key and signature size, but now bitcoin block size is limit to 1MB. So if the hardware performance will be similar to nowadays in future, then I think the block size is critical.

I read the bitcoin post quantum white paper, but there solution is that increase the block size to 16MB.

Is there any reason to store the key and signature? Is there something critical vulnerability?

Answer 1

Signatures and pubkeys are needed in order to verify transactions after the fact. Miners are not the only verifiers, and just because a transaction is in a block does not mean it is automatically valid. Other full nodes still need to verify all blocks, and that includes verifying all of the transaction in the blocks, which means verifying signatures.