Which statement regarding TFTP is not true? 

Answer options:

A. Communication is initiated over UDP port 69.
B. Files are transferred using a secondary data channel.
C. Data is transferred using fixed-size blocks.
D. TFTP authentication information is sent in clear text.
E. TFTP is often utilized by operating system boot loader procedures.
F. The TFTP protocol is implemented by a wide variety of operating systems and network devices.

D