Difference between revisions of "CIA"

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== Format ==
== Format ==
This is the current version of the CIA format. It was finalised in late 2010. (Older versions of the CIA format can be viewed on the Talk page)
This is the current version of the CIA format, it was finalised in late 2010. (Older versions of the CIA format can be viewed on the Talk page)
The CIA format has a similar structure to the [http://wiibrew.org/wiki/Wad WAD format].
The CIA format has a similar structure to the [http://wiibrew.org/wiki/Wad WAD format].

Revision as of 18:03, 19 April 2013


CIA stands for CTR Importable Archive. This format allows the installation titles to the 3DS. CIA files can compile NCCH files for installation to either the SDMC or CTR NAND. CIA files can also compile .SRL files (format for DS(i) executable images) for installation to the TWL NAND of the 3DS.

An example .CIA can be downloaded here Credit: Jl12. It includes a .cia file, the result of installation, some screenshots. Everything is decrypted/extracted for convenience sake.

Download Play child CFAs contain a CIA, which contains the Download Play child title. System Update CFAs from gamecards and Download Play also contain CIAs. On retail, CIAs are only used with Download Play child CFAs and System Update CFAs.

Development Units, are capable of manually installing CIA files via the Dev Menu.


This is the current version of the CIA format, it was finalised in late 2010. (Older versions of the CIA format can be viewed on the Talk page)

The CIA format has a similar structure to the WAD format.

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).

The CIA format is capable of containing more then one NCCH in the APP data, the TMD specifies the size of each NCCH contained in the APP data. Generally it will only contain additional NCCH files (.CFA format, such as the Manual and DLP Child) related to the main executable NCCH (.CXI format). The CIA format could be interpreted as an installable variant of the CCI format.

CIA Header

0x00 0x04 Archive Header Size (Usually = 0x2020 bytes)
0x04 0x02 Type
0x06 0x02 Version
0x08 0x04 Certificate chain size
0x0C 0x04 Ticket size
0x10 0x04 TMD file size
0x14 0x04 Meta size (0 if no Meta data is present)
0x18 0x08 Content size
0x20 0x01 Magic? Must be = 0x80
0x21 0x1FFF Magic? Must be Zero Filled

The order of the sections in the CIA file:

  • certificate chain
  • Ticket
  • TMD file data
  • APP file data
  • Meta file data (Not a necessary component)

The APP data (NCCH/SRL) is encrypted, using 128-bit AES-CBC. The encryption uses the decrypted titlekey of the ticket, and the titleid padded with zeros as the IV. To get the decrypted titlekey, the titlekey stored in the ticket must be decrypted using 128-bit AES-CBC with the 3DS common key, and the same IV as mentioned previously.


The structure of this data is as follows:

0x00 0x180 Title ID dependency list - Taken from the application's ExHeader
0x180 0x280 Reserved/Unused
0x400 0x36C0 Icon Data(.ICN) - Taken from the application's ExeFS

Obviously this section is not present in TWL CIA files, or any other CIA file which does not contain a CXI.


  • ctrtool - Reading/Extraction of CIA files. This can only decrypt the title-key for development CIAs, since retail CIAs use the AES hardware key-scrambler for the common-key keyslot.

Title Key Encryption

The unencrypted Title Key is used to encrypt the data in a CIA. The encrypted Title Key of a CIA can be found at offset 0x1BF in a CIA's Ticket. Each Title Key is encrypted with AES-CBC to get the encrypted Title Key.

To encrypt an unencrypted title key, you need:

  • Common key (as byte array)
  • Title ID (as ulong)
  • (and of course the unencrypted title key you want to encrypt) (as byte array)

The title key encryption process starts by converting the ulong (Title ID) into a byte array using by retrieving the bytes of the Title ID using BitConverter.GetBytes(). If the converted bytes (title ID) are in Little Endian, reverse those bytes. (in C# it would be Array.Reverse(byte_array_from_bitconverter)) This process makes the Title Key encryption IV.

Next, after you've gotten your Title Key's IV, you can start your cryptography transformation. Using AESManaged, where:

Key = Common Key

IV = the byte array found in the conversion process above

Mode = CipherMode.CBC

Create the encryptor (AesManaged.CreateEncryptor(key, iv)) where the key and IV are both the same as above.

Then, create a CryptoStream and a MemoryStream. The Crypto stream should start with the arguments (memorystream, aes_transform_from_above, CryptoStreamMode.Write).

Write to the CryptoStream where buffer=unencrypted_titlekey, offset=0, and count=the length of the unencrypted title key.

Use FlushFinalBlock() on the CryptoStream.

Finally, then, the encrypted title key will be available from your memory stream. (to output the calculated encrypted title key as a byte array, you can use memorystream.ToArray(), for example)

Example function: (C#)

        public static byte[] EncryptMyTitleKey(byte[] commonKey, byte[] titleKey, ulong titleId)
            // Make encryption IV
            byte[] titleidasbytes = new byte[0x10];
            for (int i = 0; i < 0x10; i++)
                titleidasbytes[i] = 0;
            byte[] bitBytes = BitConverter.GetBytes(titleId);
            if (BitConverter.IsLittleEndian)
            bitBytes.CopyTo(titleidasbytes, 0);
            // Encrypt
            ICryptoTransform transform = new AesManaged { Key = commonKey, IV = titleidasbytes, Mode = CipherMode.CBC }.CreateEncryptor(commonKey, titleidasbytes);
            MemoryStream memstream = new MemoryStream();
            CryptoStream cryptostream = new CryptoStream(memstream, transform, CryptoStreamMode.Write);
            cryptostream.Write(titleKey, 0, titleKey.Length);
            return memstream.ToArray();