Requiring an SMB file share's traffic to be encrypted

As of Windows Server 2012 and Windows 8, file shares can use SMB 3, which supports encryption and authentication for the data transfer. You can enable that with a PowerShell command. To enable encryption for all shares on the machine:

Set-SmbServerConfiguration -EncryptData $true

To enable encryption for a particular share:

Set-SmbShare "ShareName" -EncryptData $true

If you need to reverse those, just do them with $false instead of $true. Note that both of those will fail on non-Server computers.