Which service in a PKI will vouch for the identity of an individual or company?

KDC (Key Distribution Center) is a component of the Kerberos authentication protocol used to issue tickets, not a PKI identity vouching service.

A Certificate Authority (CA) is the central trust anchor in a PKI infrastructure that validates the identity of certificate requestors and then issues digitally signed X.509 certificates binding that identity to a public key. Relying parties trust certificates signed by a CA because the CA has performed identity vetting before issuance. Without a CA, there is no trusted third party to vouch for identity, making secure public-key exchanges impossible.

CR does not correspond to a standard PKI component that vouches for identity - the closest term, CRL (Certificate Revocation List), is used to invalidate compromised certificates, not vouch for identities.

CBC (Cipher Block Chaining) is a symmetric encryption mode of operation, not a PKI service or component.