3DS ROMs (NCSD) converted from CIA with seed crypto are only partially decrypted #7
Description
Thanks to @DocJr90 on another project's issue, I found a bug that affects 3DS (NCSD) ROMs converted from CIA retaining the seed crypto. On the parse_ncsd function the titleid byte array is reversed inside the for block that loops trough every NCCH, so, for NCCHs with even index, the seed is found and the file is correctly decrypted, but for NCCHs with odd index the titleid is reversed, the seed is not found and the file is incorrectly decrypted.
The byte reversal should be done only once, outside the loop. The following patch fixes the issue:
diff -u a/main.rs b/main.rs
--- a/main.rs 2025-03-31 10:29:53.524481000 +0200
+++ b/main.rs 2025-03-31 09:44:59.034743000 +0200
@@ -303,11 +303,11 @@
let mut tmp: [u8; 512] = [0u8; 512];
cia.read(&mut tmp);
let mut header: NcsdHdr = unsafe { std::mem::transmute(tmp) };
+ header.titleid.reverse();
for idx in 0..header.offset_sizetable.len() {
if header.offset_sizetable[idx].offset != 0 {
cia.cidx = idx as u16;
cia.content_id = idx as u32;
- header.titleid.reverse();
parse_ncch(cia, (header.offset_sizetable[idx].offset * MEDIA_UNIT_SIZE).clone().into(), header.titleid);
}
}