AES Keys

The S5L8900 has an AES coprocessor with the GID-key and UID-key built in.

Running The Engine
Currently, there are two ways to run the hardware AES engine. One, patch iBoot. Two, use OpenIBoot. If you want to decrypt img3 files you need to use this. The GID-key currently has not been extracted from the phone, so the only way to use it is on the phone itself.

See Easier method of getting Img3 Key / IV for an iBoot patch.

Key 0x837
Generated by encrypting 345A2D6C5050D058780DA431F0710E15 with GID-key to get 188458A6D15034DFE386F23B61D43774

It is used as the encryption key in the IMG2 File Format.

Zibri leaked this without giving an explanation of what it does.

Resources
The dev team's wiki page