Ancast image
Ancast images are encrypted and signed binaries for the Espresso processor to execute. The Espresso contains a secure boot ROM that runs upon a PowerPC hard reset, which will only boot signed code. This code comes in the form of an ancast image. Before resetting the PPC, the currently running ARM code (either IOSU or vWii IOS) must load the ancast image to the physical address 0x08000000 (Wii U images) or 0x1330000 (vWii images) for the boot ROM to verify and decrypt. The Cafe OS kernel, vWii System Menu, and vWii NANDLoader are all in the form of ancast images.
"Ancast" is an unofficial acronym for "The princess is in another castle", which is a pun introduced during fail0verflow's initial hacking efforts. It doesn't transmit any actual meaning besides that.
Structure
Header
| Start | Length | Description |
|---|---|---|
| 0x00 | 4 | Magicbytes 0xEFA282D9 |
| 0x08 | 4 | Entry offset or header size |
Entry info
| Start | Length | Description |
|---|---|---|
| 0x00 | 4 | Signature type |
| 0x04 | 56 | Signature |
| 0x84 | 4 | Unknown, maybe content ID |
| 0x88 | 4 | Unknown, maybe index and flags |
| 0x8C | 4 | Size |
| 0x90 | 14 | SHA1 |
This is followed by AES-128-CBC encrypted data.