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267 | daniel-mar | 1 | # Obfuscated filters |
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272 | daniel-mar | 3 | ## Resource location |
267 | daniel-mar | 4 | |
5 | Obfuscated standalone filters: |
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6 | - Windows resource: RCDATA\16001\0 |
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7 | - MacOS resource: 'DATA' 16001 |
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8 | |||
9 | Normal standalone filters: |
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10 | - Windows resource: PARM\16000\0 |
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11 | - MacOS resource: 'PARM' 16000 |
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271 | daniel-mar | 13 | ## Implementation |
270 | daniel-mar | 14 | |
271 | daniel-mar | 15 | Defined in **ff.h**, implemented in **make.c**: |
267 | daniel-mar | 16 | |
276 | daniel-mar | 17 | void obfusc(PARM_T* pparm, unsigned int seed); |
271 | daniel-mar | 18 | void deobfusc(PARM_T* pparm); |
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276 | daniel-mar | 20 | ### Obfuscation "Version 4" |
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22 | Introduced in **Filter Foundry 1.7.0.7** [08-Aug-2021] |
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23 | |||
24 | It is not compiler-dependant, but different between every standalone filter. |
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25 | |||
277 | daniel-mar | 26 | Windows version: |
276 | daniel-mar | 27 | The binary code of the 8BF file will be manipulated during building |
28 | in order to store the seed into the `deobfusc()` function. |
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277 | daniel-mar | 29 | The placeholder value is OBFUSC_V4_DEFAULT_SEED 0x52830517 |
276 | daniel-mar | 30 | This allows that 32 bit and 64 bit filters are "cross built". |
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277 | daniel-mar | 32 | (Theoretical) Macintosh version: |
33 | Obfuscation and deobfuscation has the seed 0x52830517, since the |
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34 | manipulation of the binary code is not implemented. |
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35 | |||
276 | daniel-mar | 36 | Algorithm: XOR shift like in version 2, but the seed is individual for |
37 | each individual built standalone filter. |
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38 | |||
39 | The value "4" will be stored at position 0x30 (this field is not used in the `PARM` resource). |
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40 | |||
271 | daniel-mar | 41 | ### Obfuscation "Version 3" |
42 | |||
267 | daniel-mar | 43 | Introduced in **Filter Foundry 1.7.0.5** [30-Jul-2021] |
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45 | It is compiler-dependant, therefore the resource cannot be exchanged between plugins! |
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46 | |||
270 | daniel-mar | 47 | Algorithm: XOR with a modified `rand()`-stream with seed that is stored at position 0x30 |
267 | daniel-mar | 48 | (this field is not used in the `PARM` resource). |
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270 | daniel-mar | 50 | 32 bit plugin is built with OpenWatcom (for Win95 compatibility) which has following formula: |
51 | |||
52 | int rand_openwatcom(unsigned int* seed) { |
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53 | *seed = *seed * 1103515245L + 12345L; |
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54 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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55 | } |
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56 | |||
271 | daniel-mar | 57 | 64 bit plugin is built with Visual C++ which has following formula: |
270 | daniel-mar | 58 | |
59 | int rand_msvcc(unsigned int* seed) { |
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272 | daniel-mar | 60 | *seed = *seed * 214013L + 2531011L; |
61 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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270 | daniel-mar | 62 | } |
63 | |||
271 | daniel-mar | 64 | ### Obfuscation "Version 2" |
267 | daniel-mar | 65 | |
66 | Introduced in **Filter Foundry 1.7b1** [20-Sep-2019] |
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67 | |||
68 | It is compiler-independant! |
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69 | |||
70 | Algorithm: [XOR-Shift](https://de.wikipedia.org/wiki/Xorshift "XOR-Shift") with hardcoded seed `0x95d4a68f`. |
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71 | |||
72 | x32 = 0x95d4a68f; |
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73 | for(i = size, p = pparm; i--;) { |
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272 | daniel-mar | 74 | x32 ^= x32 << 13; |
75 | x32 ^= x32 >> 17; |
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76 | x32 ^= x32 << 5; |
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77 | *p++ ^= x32; |
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267 | daniel-mar | 78 | } |
79 | |||
271 | daniel-mar | 80 | ### Obfuscation "Version 1" |
267 | daniel-mar | 81 | |
82 | Introduced in **Filter Foundry 1.4b8,9,10** |
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83 | |||
84 | It is compiler-dependant, therefore the resource cannot be exchanged between plugins! |
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85 | |||
86 | Algorithm: XOR with `rand()`-stream with hardcoded seed `0xdc43df3c`. |
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87 | |||
88 | srand(0xdc43df3c); |
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89 | for(i = size, p = pparm; i--;) { |
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272 | daniel-mar | 90 | *p++ ^= rand(); |
271 | daniel-mar | 91 | } |
92 | |||
93 | The plugin is built with Visual C++ which has following formula: |
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94 | |||
95 | int rand_msvcc(unsigned int* seed) { |
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272 | daniel-mar | 96 | *seed = *seed * 214013L + 2531011L; |
97 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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271 | daniel-mar | 98 | } |
99 |