Complex sentence: The PKI role that assures this binding is called the registration authority (RA), which ensures that the public key is "bound" to the individual to which it is assigned in a way that ensures non-repudiation.
Split into simpler sentences: The PKI role that assures this binding is called the registration authority (RA). The RA ensures that the public key is "bound" to the individual to which it is assigned in a way that ensures non-repudiation.