On Cisco ISR routers, for what purpose is the realm-cisco.pub public encryption key used?

A.
used for SSH server/client authentication and encryption

B.
used to verify the digital signature of the IPS signature file

C.
used to generate a persistent self-signed identity certificate for the ISR so administrators can authenticate
the ISR when accessing it using Cisco ConfigurationProfessional

D.
used to enable asymmetric encryption on IPsec andSSL VPNs

E.
used during the DH exchanges on IPsec VPNs