Secure Time Machine backup

In Terminal :

: ifconfig en0 | grep ether
: ether 00:00:00:00:00:00

Get name of your computer inside Sharing Preferences :

: Mac

Mac_000000000000

Open disk utility :

1) Create a new empty image.
2) Save as Mac_000000000000 inside Time Machine hard drive.
3) Name : Mac.
4) Size : As you wish.
5) Format : Mac OS Extended (Journaled).
5) Encryption 128 or 256bits.
6) Partition : Single partition - Apple Partition Map.
7) Image format : sparse bundle disk image.
8) You are asked to enter a secure password.

: Drag and drop secure password from login to system.
: Inside Time Machine Preferences select Time Machine hard drive containing the new secure empty image.

Delete a Certification Authority from Keychains

1)Backup Certificates.

sudo cp /System/Library/Keychains/SystemRootCertificates.keychain /System/Library/Keychains/SystemRootCertificates.keychain.bak

2)Extract "SHA1" from the specific Certificate.
3)Delete Certificate.

sudo security delete-certificate -Z "SHA1" /System/Library/Keychains/SystemRootCertificates.keychain

Disable AirDrop

To disable AirDrop :

defaults write com.apple.NetworkBrowser DisableAirDrop -boolean YES

To enable AirDrop :

defaults write com.apple.NetworkBrowser DisableAirDrop -boolean NO