Once the Salt minion is authenticated to the Salt master, an AES key is used for encrypting communications between the master and minion. See https://docs.saltproject.io/salt/user-guide/en/latest/topics/security.html for more details on this subject.
SaltProject - all versions
Tanzu Salt - all versions
Aria Config - all versions
VCF - all versions
256-bit level AES encryption is used between the master and minion once the minion is authenticated with the Salt master.