Company A and Company B have just merged and each has its own Public Key Infrastructure (PKI). What must the Certificate Authorities (CAs) establish so that the private PKIs for Company A and Company

Poly key exchange is not a recognized PKI, cryptographic, or networking standard and describes no real mechanism for establishing CA trust relationships.

In cross certification, each CA issues a certificate to the other CA, creating a trust path so that entities in Company A's PKI can validate certificates issued by Company B's CA and vice versa. This mechanism enables two private PKIs to interoperate without requiring a shared common root CA, making it the standard solution when merging organizations with separate PKI infrastructures.

Poly key reference is not a defined term in any PKI or cryptography specification and has no technical meaning in the context of certificate authority trust establishment.

Cross-site exchange is not a PKI concept - the term cross-site belongs to web security (e.g., cross-site scripting, cross-site request forgery) and has no relevance to certificate authority trust models.