Hi Simone,
you can obtain the keystore through Eclipse in the message monitoring tool. Simply double click on the account object in the lower left corner of the node explorer. However, to download the key store, this may require additional user privileges.
Can you elaborate what you actually try to accomplish? The HCI keystore is only relevant if you want to add the public key from ERP. Any other public keys (from C4C) can be uploaded via Eclipse or the WebUI.
Best regards,
Ralf.