Default Trying to understand locked bootloaders

I get what a bootloader is--the low level programming that checks everything and then boots the OS. And I have read that when they say "locked bootloader" it means "encrypted bootloader".

Have previous bootloaders been un-encrypted and thus made flashable? Or was some "exploit" found that enabled the bootloader to be replaced with one that would be unencrypted and thus ROMs could be flashed?

It sounds like the bootloader being locked/encrypted prevents much being done in the way of custom ROM flashing. So at this point we have Safestrap, unless that doesn't work on the AT&T g900a.

So, what are the designers working on at this time--unencrypting the bootloader, finding a way to simply replace it, or using something like Safestrap to create a space where a different ROM can be placed and the bootloader bypassed in some way?

I suppose I am curious to find out just how tough this locked bootloader problem is for the devs.

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