CIA stands for CTR Importable Archive. These files contain a compiled application which can be installed on CTR NAND, TWL NAND (part of the NAND used by DSi applications) and on the SD card. CIA files can be created with the Nintendo 3DS SDK and installed on the 3DS test units by the Dev Menu.
The CIA format based on WAD format, so the structure is very similar to the WAD structure.
The file is represented in little-endian.
The data is aligned in 64 byte blocks (if a content ends at the middle of the block, the next content will begin from a new block).
This is a 32 bytes long header (8 x uint32).
|0x00||0x04||Archive Header Size (=0x2020 bytes) (Starts with 0x80 @ offset 0x0020)|
|0x04||0x04||Reserved = 0|
|0x08||0x04||Certificate chain size|
|0x10||0x04||TMD file size|
|0x14||0x04||Banner size (0 if no banner)|
|0x18||0x04||APP file size|
The order of the sections in the header also is the order of them in the CIA file:
- certificate chain
- TMD file data
- APP file data
The data of the files is decrypted.
The banner starts with a 0xF0 large data block, whose purpose is currently unknown. Then at offset 0x400 into the banner section is the actual banner, which contains information about the creator and title of the app (you can see them in the system settings):
|0x05||0x04||Reserved = 0|