For starters, S-Off and root ARE TWO COMPLETELY DIFFERENT THINGS!
HTC has been securing their phones by locking the internal flash memory (NAND or eMMC)(eMMC in our case) to stop it from being written to, unless the file being flashed is signed by a private key only known to HTC. This is controlled by a flag (@ secuflag) and is identified as the device being S-ON. Telling the HBoot the device is Security Off (S-OFF) stops this check for the key, and allows us to write anything to any partition, which is what we are aiming for.
There are actually two levels of S-OFF. The Bootloader (HBoot) and the Radio. Getting S-Off on the HBoot gives us everything we need, but doesn't actually turn off the @ secuflag which is set in the radio - instead, the HBoot ignores it and therefore thinks it is S-Off, but this is not TRUE S-Off. It is possible to flash a HBoot that believes the Radio is set to S-OFF, as the HBoot is responsible for setting that flag.
Once the HBoot on the phone is S-OFF, we can write to all the partitions and basically do whatever we want, but it is possible to go one step further. Flashing a radio that is S-OFF and actually setting the @ secuflag to S-off gives us 100% total access to every part of the phone and it's software, as it becomes network unlocked allowing you to use any SIM and also allows you to flash a ROM from any carrier (known as Super CID). It also makes it practically impossible to permanently loose root no matter what you flash. Once you have radio S-OFF, it makes it much easier to flash new HBoots and ROMs even if you flash something that is locked down tight.
Setting the Radio to S-Off is not necessary, and gaining S-OFF on the HBoot is more than most people will ever need. Radio S-Off is just the last step of the puzzle, but it is worth noting that you can permanently brick your phone if flashing a radio or a HBoot, if either of these go wrong you will end up with a shiny expensive paper weight so there is risk involved. If this helped you in any way then feel free to click on the thanks button. Meanwhile, happy hunting!
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