AWS Storage Gateway now supports security level options for data transferred between the File Gateway and SMB clients. You can enforce encryption and signing on client requests, or use client-negotiated defaults, helping you meet organizational requirements for security and client compatibility. 

from Recent Announcements https://aws.amazon.com/about-aws/whats-new/2019/06/file-gateway-adds-options-to-enforce-encryption-and-signing-for-smb-shares/