"Attestor" is a word in ENGLISH

A declaration or avowal of one's own act, to give it legal validity; as, the acknowledgment of a deed before …

In French law, denotes a docu* ment, or formal, solemn writing, embodying a legal attestation that something has been done, …

To attest by writing one's name beneath; as, officers subscribe their official acts, and secretaries and clerks subscribe copies or …

One who vouches, or gives witness or full attestation, to anything.