I have some unity3d files which some are encrypted like this:
The encrypted chunk starts at 0x60 for all files.
This 2 bytes stored in little endian mark the end of the encrypted chunk:
From 0x61 up to one byte before the offset above, every byte must be xored with the previous byte:
Decrypted file:
Encrypted file:
XOR 0x61 with 0x60:
0x62 xor with 0x61, 0x63 with 0x62 and so on up to chunk end.
This byte from 0x60 should be xored with the one from 0x06:
Now it looks like the decrypted file:
I don't know if the best approach for this would be to do the process backwards in the byte order because of changing the previous values which would be read for each byte.
A simple way to put this could be xor "0x61 up to stored offset minus 1" with xor key being "0x60 up to stored offset minus 2" and then doing the "0x60 xor with 0x06". Maybe.
Then the first few bytes should be replaced by "55 6E 69 74 79 46 53 00" which would read as "UnityFS\x00"
Here is a sample file and the same file manually decrypted: https://mega.nz/#!Y8oknYTZ!IR8XNKTmiSuZ ... f2xW-vrSmQ
Doing this manually for each file is extremely tiring but I have no idea how to write a script and have no coding knowledge.