| Component | Description |
|-----------|-------------|
| Encryption | 3DS titles are encrypted with a combination of AES‑CTR and RSA using per‑title keys stored in the console’s secure module. The keys differ per region (e.g., 0x00040000 for US, 0x00048004 for JP). |
| Dumping | To obtain a clean copy, a home‑brew tool (e.g., GodMode9, 3DShell, FBI) reads the cartridge’s NAND and writes the raw binary. The dump includes a header (NCCH) that flags the encryption status. |
| Decryption | Tools such as 3DScrypt, Decrypt9WIP, or Citra’s built‑in decrypter (when running the dump through the emulator with proper keys) strip the encryption, outputting a decrypted NCSD/NCCH structure. The result is a set of ARM9/ARM11 binaries, exefs, romfs, and asset archives (e.g., .szs compressed files). |
| Undubbing Process | 1. Identify voice files – In SMT IV they reside in romfs/voice/jp/ as .bcwav and .bcstm. 2. Remove or replace – Deleting the directory or swapping it for a placeholder reduces size. 3. Re‑pack – The modified romfs is re‑compressed (szs tools) and the NCCH header is updated. 4. Re‑sign – The final ROM must be signed with a valid title key (or a dummy key if used only on emulators). |
| Resulting Size | The original US version is ~1.05 GB. After undubbing, the ROM typically shrinks to ~970 MB, a ~7 % reduction. The smaller file loads marginally faster on low‑end 3DS hardware and on PC emulators such as Citra. |
Note: The steps above are provided only for educational insight into how ROMs are structured and how fan projects manipulate them. The actual distribution of copyrighted ROMs, decryption keys, or tools that bypass Nintendo’s security is illegal in most jurisdictions. Shin Megami Tensei IV -UNDUB- 3DS -Decrypted- ROM
The label "Decrypted" is crucial for the modern player. A standard 3DS ROM is encrypted to work only on specific hardware. A decrypted ROM has had that protection stripped away, meaning it is versatile. Note: The steps above are provided only for
Citra, the open-source 3DS emulator, received a "Vulkan" backend update that dramatically improves performance for SMT IV. The label "Decrypted" is crucial for the modern player