  The 3GPP 5G Service-based Architecture (SBA) security specifications leave
several details on how to setup an appropriate Public Key Infrastructure (PKI)
for 5G SBA, unspecified. In this work, we propose 5G-SBA-PKI, a public key
infrastructure for secure inter-NF communication in 5G SBA core networks, where
NF refers to Network Functions. 5G-SBA-PKI is designed to include multiple
certificate authorities (with different scopes of operation and capabilities)
at different PLMN levels for certification operations and key exchange between
communicating NFs, where PLMN refers to a Public Land Mobile Network. We
conduct a formal analysis of 5G-SBA-PKI with respect to the desired security
properties using TAMARIN prover. Finally, we evaluate 5G-SBA-PKI's performance
with "pre-quantum" as well as quantum-safe cryptographic algorithms.
