Decoding an arbitrary block of NSData?

Question

If I have an arbitrary block of NSData as a hex value, is there a way to determine what the object might have been before it was archived or serialized? I don't mind a few guess and check methods, but I need some pointers in the right direction.

I have an NSData object with some hex in it. What methods of NSData should I look at? Are there other classes to try as well

Don't want to scare people away from answering, but I have a file of game data which was likely encoded using a Cocoa Touch class. The data, when viewed in a hex editor, shows gibberish and a username, which leads me to suspect that it's an archived or encoded object of sorts. I have copied the hex from the hex editor into a sample project which I am using to try and unarchive the data.

I don't believe this is related to the 3d format, the file extension is arbitrary.

Here's the data. I'm hoping it doesn't get lost in translation:

'µköXN[ÎÀü÷h/F9ó9Vìñ°ceE¸z¶=Hmoshbermú«ó¼Ppù#ÝVÔ=4â®L,K;Êç;ASÀ&Ë÷ëÓ%È;Úf¬G}tmQ;µéüø_87´y©ã©!߶óQòAçÛl©âSG4S½3ýJת9äô¡wxiD²M¼ÏB]39øþ:óñ7ª¾÷躣È3Ï¢ÍEFÍ¢ª»r]BmÁ'Ò+åygÞÅQ?luó>÷ú¼è6¸|}[¼[¶Ñ¦g!\OÎÒJSE..pSß&_ÈEäø)6òëó¨¼2¶ð°æà`ï7Ë=Ã¥:cƧ=L4qG-"µ(ÐÝïß ÓãXkÀ4fzæ·p\ññT<tu¥Æ©;Ìn4£³Ï¢ÌFåG´

And the corresponding hex:

27 B5 6B F6 01 00 00 00 58 4E 5B CE C0 FC F7 68 2F 46 86 87 83 39 F3 39 9E 56 EC F1 B0 63 9E 65 45 B8 7A B6 3D 07 99 48 6D 6F 73 68 62 65 72 6D 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 90 86 FA 03 0E AB F3 BC 0B 50 70 F9 23 DD 87 56 03 D4 3D 34 90 E2 AE 4C 2C 94 9E 8E 15 4B 0C 83 8C 3B 03 CA E7 3B 1B 41 53 C0 26 04 CB F7 EB D3 25 C8 3B DA 66 8A AC 47 7D 8A 7F 74 6D 51 3B B5 19 E9 FC F8 5F 38 37 B4 11 0C 79 A9 12 E3 A9 21 DF B6 F3 51 F2 41 E7 DB 85 02 9F 6C A9 E2 53 47 1F 34 86 53 BD 33 FD 4A D7 AA 39 C3 A4 F4 A1 77 78 69 44 B2 4D BC CF 42 5D 33 39 F8 FE 97 3A 81 F3 F1 10 37 AA BE 86 91 F7 1F E8 83 BA A3 C8 33 CF 1D A2 CD 45 7F 46 1F CD A2 AA BB 1A 72 5D 42 02 6D C1 0F 27 D2 2B E5 0B 79 67 DE C5 1A 51 3F 14 6C 75 F3 3E F7 FA BC E8 36 8E B8 7C 02 1C 7D 01 00 92 8C 19 5B BC 5B B6 D1 A6 67 7F 21 5C 84 13 4F CE 0C D2 4A 53 19 82 45 1B 2E 2E 96 70 53 DF 26 5F C8 1C 45 8F E4 F8 29 36 F2 EB 9D 95 F3 A8 BC 32 B6 F0 B0 E6 91 98 1A E0 99 60 EF 37 CB 3D C3 A5 3A 63 0C C6 A7 3D 4C 34 71 47 2D 22 B5 28 D0 DD EF DF 09 D3 E3 58 6B C0 17 34 66 7A E6 B7 70 5C F1 F1 54 3C 74 94 75 A5 C6 15 A9 9E 14 3B CC 15 10 83 6E 34 A3 B3 CF 0F A2 9C CC 8E 46 8C E5 00 00 47 B4 17 05 00 00 00 00

If anyone cares to help figure this out it would be much appreciated.

Answer 1

If I have an arbitrary block of NSData as a hex value, is there a way to determine what the object might have been before it was archived or serialized?

Not really. That's about as 'trivial' as reading arbitrary files correctly without the use of a UTI, extension, MIME type. Of course, your program would also need to support reading of all those files/formats.

I don't mind a few guess and check methods, but I need some pointers in the right direction.

You need to narrow your problem/inputs down, if you don't want an impossibly difficult task.

I have an NSData object with some hex in it. What methods of NSData should I look at?

It's just a data blob of length bytes. It could represent anything -- if you don't know where it came from.

Are there other classes to try as well?

Perhaps you would start by saving all your data via NSCoder or another serializer/archiver which offers some introspection and support for you to enter your own information (which would be comparable to a UTI or MIME type).

Edit:

Don't want to scare people away from answering, but I have a file of game data which was likely encoded using a Cocoa Touch class. The data, when viewed in a hex editor, shows gibberish and a username, which leads me to suspect that it's an archived or encoded object of sorts. I have copied the hex from the hex editor into a sample project which I am using to try and unarchive the data.

Using these APIs, the data may be represented multiple ways. You're probably facing something within the domain of 1) a proprietary file format through 2) a keyed archive.

The latter is easier for nontrivial data representations. You would need to define any objc classes you do not have available when unarchived. In that case, a few sample representations would offer a rough outline of the data structures you will need (under conventional implementations). It could also be an archive similar to an NSDictionary, if the unarchiver is capable of opening it. This is a problem which is easier than with other langs, since archiving often falls back on keys and values mapped to members in Cocoa.

Edit2:

The file came from the Draw Something directory. It's called gamedata.i3d

(shrug)