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

CBC (Cipher Block Chaining) is a symmetric encryption mode of operation, not a PKI component involved in identity validation.

KDC (Key Distribution Center) is a Kerberos authentication component that issues tickets for session-based authentication, not digital certificates in a PKI.

A Certificate Authority (CA) is the trust anchor of PKI - it verifies an applicant's identity and then issues a digitally signed certificate binding that identity to a public key. Any party that trusts the CA implicitly trusts the identities asserted in its issued certificates, which is the core vouching function of PKI.

CR typically refers to Certificate Repository or Certificate Revocation - a storage or revocation mechanism - not the entity that vouches for identity.