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Ymgve
Registered: May 2002
Posts: 84 |
Laurin disk "encryption" broken
I did a little research after hearing about the Laurin disk encrypter/hider, and managed to crack the (rather weak) encryption it uses.
So if any of you have any old disks you've forgotten the password to, here's my tool: https://github.com/ymgve/laurin-decrypt (Sorry for the low quality code) |
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Count Zero
Registered: Jan 2003
Posts: 1920 |
Release on CSDb or didnt happen! :) |
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lA-sTYLe
Registered: Sep 2003
Posts: 63 |
confirmed working ;-) |
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AlexC
Registered: Jan 2008
Posts: 298 |
Very interesting. Where I can find original tool? |
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Ymgve
Registered: May 2002
Posts: 84 |
Laurin is the one I studied, at least |
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hedning
Registered: Mar 2009
Posts: 4720 |
Laurin-decrypt |
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Style
Registered: Jun 2004
Posts: 498 |
Any details on the encryption method?
I always like to giggle at what people classified as "encryption" back in those days. I "cracked" a tacops anti-cheat proggy once that was basically using EOR "encryption". So much work went into it, but the stream could be broken just by staring at the bytes long enough. |
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Ymgve
Registered: May 2002
Posts: 84 |
It takes an 8 character password, which it compresses down into 4-byte key, which is then "obfuscated" (but also restricts the keyspace) by using the BASIC ROM as a look-up-table. The final 4-byte key is then used for a function that works on individual bytes by doing add/xor/add/xor with the respective bytes of the key.
Encryption is done by RLE encoding the directory track and then encoding it. It's then written back to the directory track, with a fake track 18.0/18.1 placed instead.
You'll note that I only talked about the directory - Laurin doesn't even look at the actual file data, it only touches the directory track. So even if my program failed you would be able to recover the files on disk with any standard recovery tool.
Also, if any of you want to scan your collection for Laurin disks or something, it checks if byte 3 of sector 18.0 is 0x69 to verify that a disk is actually encrypted. |
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iAN CooG
Registered: May 2002
Posts: 3186 |
Some probably had hundreds of these disks, and have reused them because they appear as empty formatted "testdisk". Very clever way to loose your precious data :D |
