| Have you ever wondered how gg managed to make CRC checksum of Maria+Holic s1e12 equal to FFFFFFFF, or how FFF got their Yuru Yuri s2e11 to be 11111111? Well, I certainly did! So I've done some digging, found and studied some complicated mathematical research articles, took time to digest them and here I am now, delivering you CRCManip: a tool that allows you to freely manipulate your files' CRC32 checksums. How's that possible? Well, it's not possible unless you change file contents. But fortunately enough, Matroska containers and most binary files don't mind additional bunch of bytes at the end of their contents, and this is exactly what this program does: it adds 4 bytes at the end of given file so that it computes to desired checksum afterwards. In other words, .mkv files open perfectly fine even after patching! Project on github: click Binaries for Windows: click Supported platforms: - GNU/Linux - MS Windows Screenshot of main window + verification that it works:  (For those who wonder about the "Checksums" tab in Explorer, I use HashCheck Shell Extension.) |
rr-Jul 5, 2015 9:55 AM
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| I don't really quite understand these things...but why would you want to change a CRC value? o_o |
HauntingShock said: Just for the sake of doing it. I used one of the previous iterations of rr-s crcmanip when making patches for Nisemonogatari. Instead of including a checksum in the filename you could say that all your releases' checksums are 00000000 or FFFF<season><episode number>.I don't really quite understand these things...but why would you want to change a CRC value? o_o |
fri said: HauntingShock said: Just for the sake of doing it. I used one of the previous iterations of rr-s crcmanip when making patches for Nisemonogatari. Instead of including a checksum in the filename you could say that all your releases' checksums are 00000000 or FFFF<season><episode number>.I don't really quite understand these things...but why would you want to change a CRC value? o_o Oh...I didn't quite understand but it's related to patches. lol :D |
| Always wondered how they manage it haha, thx for the info! |
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| I have respect that you put your time in this, but the purpose of CRC is gone. :P |
| Well, if the file in question arrives to you broken not due to someone's malicious intent, the checksum (whatever it may be, patched or not) can still effectively be used to test if file is okay since the chance for checksum collision is stlil 2^-32. Troubles appear only if you want to identify the file basing on its checksum, instead of its file name (for example, you search for the file on the Internet by its checksum, or decide whether ep is v2 or v3 basing on the checksum, or even guess what's the episode number or series name.) Then again, this is hardly a problem if the encoder/user is rational and embed such information in the checksum itself, like fri suggested (for example: "111-version-season-episode"). As for exactly why change CRCs: because it's  |
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