This document is about the format of CTR cart images (CCI), which is also the format of 3DS ROM dumps.
Overview
CCI files start with a NCSD header, followed by 3 CXI blocks. The first block usually starts at 0x4000. While it is unknown what each CXI block is for, the first one is most likely the main program code since it is much bigger than the others.
NCSD header
| OFFSET | SIZE | DESCRIPTION |
|---|---|---|
| 0x000 | 0x100 | RSA-2048 signature of the NCSD header, using SHA-256 (needs to be confirmed) |
| 0x100 | 4 | Magic ID, always 'NCSD' |
| 0x104 | 4 | Size of the CCI image, in media units (1 media unit = 0x200 bytes) |
| 0x108 | 8 | Title/Program ID |
| 0x120 | 4 | Offset to the first CXI in media units |
| 0x124 | 4 | Size of the first CXI |
| 0x130 | 4 | Offset to the second CXI |
| 0x134 | 4 | Size of the second CXI |
| 0x158 | 4 | Offset to the third CXI |
| 0x15C | 4 | Size of the third CXI |
| 0x18C | 4 | Unknown (always 0x00000101) |
| 0x190 | 8 | Partition ID of the first CXI |
| 0x1A0 | 8 | Partition ID of the second CXI |
| 0x1C8 | 8 | Partition ID of the third CXI |
| 0x200 | 4 | Always 0xFFFFFFFF |
| 0x300 | 4 | Used ROM size in bytes |
| 0x320 | 16 | Unknown |
Parts of the first CXI block's NCCH header are found around 0x1000 for whatever reason.
CCI images may not include all three CXI blocks. For example, Ghost Recon: Shadow Wars lacks the second CXI. Entries at 0x130, 0x134 and 0x1A0 in its NCSD header are zero.