Default Need help downgrading.

So i have a Galaxy S3 from Verizon. Earlier i tried to downgrade my phone to 4.1.2. So i got everything i need and i open odin thenwhen i click start it will only say fail.
<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> KIES_HOME_I535VRBMF1_1152558_REV09_user_low_ship.t ar.md5 is valid.
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/004> Odin v.3 engine (ID:4)..
<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> sbl2.mbn
<ID:0/004> NAND Write Start!!
<ID:0/004> sbl3.mbn
<ID:0/004> aboot.mbn
<ID:0/004> FAIL! (Auth)
<ID:0/004>
<ID:0/004> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)

Can someone please help me. i have also broke my phone to where it says "Firmware upgrade encountered an issue. Please use Software Repair Assistant & try again." and it wont boot up. If someone could help me and explain it to where noobs would understand it i would be very grateful.