mobile

I have an AT&T Samsung Galaxy S5 running lollipop 5.0. I can not find any way to root this device on 5.0, so I tried to downgrade to 4.4.2 using odin and stock firmware from samsung. It has failed everytime.

Message in Odin:
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> G900AUCU1ANCE_G900AATT1ANCE_G900AUCU1ANCE_HOME.tar .md5 is valid.
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/004> Added!!
<ID:0/004> Odin engine v(ID:3.1005)..
<ID:0/004> File analysis..
<ID:0/004> SetupConnection..
<ID:0/004> Initialzation..
<ID:0/004> Get PIT for mapping..
<ID:0/004> Firmware update start..
<ID:0/004> SingleDownload.
<ID:0/004> aboot.mbn
<ID:0/004> NAND Write Start!!
<ID:0/004> FAIL! (Auth)
<ID:0/004>
<ID:0/004> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)

Message in download mode on phone:
ODIN MODE
Product Name: SM-G900A
CURRENT BINARY: Samsung Official
SYSTEM STATUS: Official
REACTIVATION LOCK(KK): OFF
KNOX WARRANTY VOID: 0x0
QUALCOMM SECUREBOOT: ENABLE(CSB)
RP SWREV: S1, T2, R1, A3, P1
SECURE DOWNLOAD : ENABLE
UDC START
SW REV CHECK FAIL : [aboot]Fused 3 > Binary 1

I ask that someone help me with a method to root 5.0, or downgrade to 4.4.2 so I can towelroot.