CIA: Difference between revisions

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 Obviously this section is not present in TWL CIA files.
+== 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 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 ID 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#)
+<pre>
+        public static byte[] EncryptMyTitleKey(byte[] commonKey, byte[] titleKey, ulong titleId)
+        {
+            byte[] titleidasbytes = new byte[0x10];
+            for (int i = 0; i < 0x10; i++)
+            {
+                titleidasbytes[i] = 0;
+            }
+            byte[] bitBytes = BitConverter.GetBytes(titleId);
+            if (BitConverter.IsLittleEndian)
+            {
+                Array.Reverse(bitBytes);
+            }
+            bitBytes.CopyTo(titleidasbytes, 0);
+            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);
+            cryptostream.FlushFinalBlock();
+            return memstream.ToArray();
+        }
+</pre>