Either: a Nintendo 3DS image may contain encrypted or decrypted data. The filename extension—such as .3ds, .cci or .cia—does not tell you which. The key distinction is the encryption state of the content inside its NCCH partitions.
What “encrypted” means in a 3DS file
NCCH (Nintendo Content Container Header) is the core format used to store title content. It can contain a CXI executable image or a CFA non-executable archive. A CXI may include an NCCH header, an extended header, an access descriptor, an optional plaintext region, ExeFS and RomFS.
NCCH format references describe the extended header, ExeFS and RomFS as encrypted by default with 128-bit AES CTR, unless the NCCH flags set NoCrypto. Some regions may be plaintext, so it is not accurate to say every byte in every 3DS image is encrypted. The format documentation also distinguishes a “menu info” group—the extended header, ExeFS header, icon and banner—from the remaining executable files and RomFS, with key selection affected by NCCH flags. See the NCCH format reference and CXI format reference.
Why the extension does not settle it
Extensions describe a container or packaging convention, not necessarily the crypto state of the content inside it.
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| Format or extension | What it identifies | What it says about encryption |
|---|---|---|
.3ds / CCI |
A game-card image container that can hold NCCH partitions. | Does not establish encryption state. 3dsconv documents CCI images that may be decrypted, encrypted with original NCCH crypto, or encrypted with a zero key. |
| CIA | A CTR Importable Archive package. | The extension alone does not prove the state of its inner NCCH data. A community decryption project’s README describes CIA content as having an outer title-key/AES-CBC layer and inner NCCH/AES-CTR content; that is the project’s implementation description, not an official Nintendo specification. |
| NCCH | A content partition format used within title files. | Its relevant regions are encrypted by default unless NoCrypto is set; plaintext regions are also possible. |
The distinctions between CCI input and CIA output, and among encryption states, are described in the 3dsconv project. A changed extension after conversion is not proof that the content was decrypted.
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Encryption can vary by key variant
NCCH encryption is not one uniform mode across all titles. The NCCH reference describes key-slot selection changes across generations: original slot 0x2C, later slot 0x25, and New 3DS variants using slots 0x18 and 0x1B. These details concern how compatible software identifies and handles encryption; they do not let you infer a file’s state from its name.
Retail and developer-unit encryption can differ. The 3DS-Decrypt project says its scripts support retail keys and that developer-encrypted ROMs require developer KeyX values. Its notes are specific to that project, not a universal specification. See the 3DS-Decrypt project documentation.
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Conversion is not the same as decryption
Converting a CCI/ .3ds image to CIA changes its packaging. The 3dsconv documentation explicitly cautions that conversion does not necessarily decrypt the content or change the output’s encryption state; a converted CIA may still contain encrypted NCCH data. Its documentation also says original-NCCH decryption requires a protected ARM9 bootROM copy.
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How to interpret a file label
- “Encrypted” or “decrypted” should refer to the state of NCCH content, not just the file extension.
- “Zero-key encrypted” is a distinct state documented by 3dsconv; do not assume it is identical to either original-NCCH encryption or decrypted content.
- “CCI,” “.3ds” or “CIA” identifies packaging or container type, not a guarantee about crypto state.
- “Converted” means the container was changed; it does not by itself mean the contents were decrypted.
The technical references are community-maintained format documentation and project documentation. No prevalence figure establishes what proportion of 3DS images are encrypted versus decrypted, so a general percentage would be misleading.
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