In order to encrypt your traffic you have to use certificates. Certificates have a double role in this scenario; they are used for the authentication of nodes and also for the encryption of replication traffic.
Note that you must have an Enterprise Certificate Authority server in your domain. Enterprise Certificate Authority is a server with the Active Directory Certificate Services role installed on it.
To set up an Enterprise Certificate Authority server, refer to the article at the following link:
Before we can equip our Hyper-V hosts with a certificate for data encryption, we need to create a certificate template. To do ...