[LG G Pad 7 Questions & Answers] PRichardson:
Bumping (Cryptographically Signing) Bootable Images For LG (v410) G-Pad 7" AT&T LTE

3's&7's, ...

My understanding is that this is definitely possible.

All the source code for CyanogenMod is available in the ...

CyanogenMod Github repo: http://github.com/CyanogenMod

As explained in the ...

Official CyanogenMod Wiki: http://wiki.cyanogenmod.org/

But, even more important than the ability to boot a system image (kernel, plus OS) that passes the cryptographic signature check (which the newly 'opened'/Kanged, Python scripts 'fix', aka., 'Bump'), we need a decent 'custom' recovery, which we can flash over the top of the crappy OEM recovery which is preinstalled on all LG G-Pads.

Here is an example of someone who followed some tutorials and with a little help built (compiled) the TWRP (Team Win Recovery Project) custom recovery for the LG G3 Phone:

http://xdaforums.com/att-lg-g3/orig-development/recovery-twrp-2-8-2-0-t2959606

It is assumed you are comfortable with Linux shells in order to complete these tutorials, but you may also want to take a Wikipedia-gander at the 'device-tree' concept, and the posts earlier in this same thread (especially my own) which provide some info on the partition and layout for the v410, prior to building TWRP for it.

Here is the source for the custom TWRP recovery that he built:

https://github.com/AndroidUser00110001/device_lge_d850-twrp

Here is a version of TWRP for the G-Pad 8.3" (warning, this MUST be old because it is well-known that contrary to the OP, Loki no longer works on newer GPad models)

http://teamw.in/project/twrp2/213

There are lots of tutorials out there with HowTo's on building TWRP, but here is the one that they (the TWRP Devs) link to on their official website:

http://rootzwiki.com/topic/23903-how-to-compile-twrp-from-source/

And here is a tutorial for building TWRP for Samsung devices:

https://github.com/smasher816/Team-Win-Recovery-Project-Samsung

It is important to note that whenever certain hardware is different (for example the 'board', aka mobo), or different sized partitions, then the TWRP must be compiled from scratch for that device specifically. So sometimes devices have the same advertising model number (common marketing name) but are still different enough in actual hardware (yes that is stupid) that the same compiled code (aka, binaries) of TWRP is not interchangeable (compatible) between those devices. Such might be the case between the XYZ-Pad (9" GSM) in the USA versus the XYZ-Pad (9" GSM) International. They might have slightly different SUB-model numbers., such as v408a and v408b, as used by developers and carriers but not generally advertised.

Now, it turns out that the custom recovery is itself like a little 'OS' in the sense that it loads into memory and execute from there, so (I guess?) it can be cryptographically signed too. And just like the main system image this signature can be checked before it is fully 'allowed' to complete it's initial (aka, init*) processes.

In normal PKI cryptography (such add GPG, aka, OpenPGP, aka, GnuPG) it is almost impossible to derive the private (matching) key from the public key. But in reality its both MORE complicated than this in the intended strategy and possibly less complicated than this in how LG attempted an alternative (weaker) implementation. For example, here is a discussion and dissection of how Motorola implements 'Secure Boot' using something called QFuses:

http://blog.azimuthsecurity.com/2013/04/unlocking-motorola-bootloader.html

But here is how simple it was to circumvent this security measure (the original method, closed spouse via team 'CodeFire'):

Overview: http://www.xda-developers.com/android/bump-lg-g3-on-the-fly/

OP: http://xdaforums.com/att-lg-g3/orig-development/bump-sign-unlock-boot-images-lg-phones-t2935277

... and here is the 'open-source' (and sort of Kanged) python script to bump/sign images:

http://xdaforums.com/lg-g3/orig-development/tool-bump-sign-boot-images-t2950621

Hope this help ;)

* the 'init' that you likely read and hear about most of the time actually happens later, but the idea is the same (you typically are trying to run some code or scripts early at boot).

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