tx-malleability who re-signed the tx?

Question

It would be really great if there was a way to loop through all the txids in a new block and be able to check if you (can) sign your original transaction the same way it was re-signed - that it matches the new txid

but i guess it would require that you also hold the private key of whom ever resigned your tx :/

Question(s):

if I somehow had the public key of whom ever re-signed my tx what could i observe from the new malleat-ed txid?

would i be able to run a test on the new txid to see if it is somehow related to my tx and/or my original txid?

If so how would I go about accessing the public key that relates to the private key that re-signed the txid in a new block?

Assumption(s):

the public key is named public because i could possibly/somehow have access to it easily...(??)

If the pub key is not readily accessible (massive assumption) peers on the bitcoin network should supply the public key part of their keys (to other peers) that is the pair to the private key they use to malform/re-sign transactions...(!!?)

Answer 1

Actually, nobody else can create a valid signature for your transaction inputs, as they do not possess the private keys to do so.

When a transaction is malleated by a third party, it is not re-signed, merely it's signature is changed. ECDSA signatures are malleable, in that taking the negative of number S (modulo the curve order) does not invalidate them. As the TXID is created by hashing the complete transaction data, this will result in a new valid transaction with identical payload except for a new TXID.