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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 | |
292 | daniel-mar | 15 | Defined in **ff.h**, implemented in **obfusc.c**: |
267 | daniel-mar | 16 | |
292 | daniel-mar | 17 | // Only implements V5. Returns a seed that needs to be stored in the executable code. |
18 | unsigned int obfusc(PARM_T* pparm); |
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282 | daniel-mar | 19 | |
20 | // In V1+V2: Seed is hardcoded |
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292 | daniel-mar | 21 | // In V3: Seed is in PARM (field "unknown2") |
22 | // In V4+V5: Seed is in the program code and will me modified with a binary search+replace |
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271 | daniel-mar | 23 | void deobfusc(PARM_T* pparm); |
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292 | daniel-mar | 25 | ### Obfuscation "Version 5" |
26 | |||
27 | Introduced in **Filter Foundry 1.7.0.8** |
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28 | |||
29 | Obfuscation version 5 is the same as version 4, but there is a constraint |
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311 | daniel-mar | 30 | that the seed must be equal to the CRC32b checksum of the deobfuscated PARM. |
292 | daniel-mar | 31 | This is done to check the integrity of the deobfuscation. |
311 | daniel-mar | 32 | |
309 | daniel-mar | 33 | Also, the xor-shifting is intentionally incompatible with version 4 |
311 | daniel-mar | 34 | (to avoid downgrade-attacks) by XORing the initial seed with 0xFFFFFFFF. |
292 | daniel-mar | 35 | |
276 | daniel-mar | 36 | ### Obfuscation "Version 4" |
37 | |||
292 | daniel-mar | 38 | Introduced in **Filter Foundry 1.7.0.7** |
276 | daniel-mar | 39 | |
40 | It is not compiler-dependant, but different between every standalone filter. |
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41 | |||
277 | daniel-mar | 42 | Windows version: |
276 | daniel-mar | 43 | The binary code of the 8BF file will be manipulated during building |
282 | daniel-mar | 44 | to store the seed into the `deobfusc()` function. |
45 | The placeholder value is `OBFUSC_V4_DEFAULT_SEED 0x52830517` |
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46 | This allows that 32-bit and 64-bit filters are "cross built". |
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276 | daniel-mar | 47 | |
277 | daniel-mar | 48 | (Theoretical) Macintosh version: |
49 | Obfuscation and deobfuscation has the seed 0x52830517, since the |
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50 | manipulation of the binary code is not implemented. |
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51 | |||
282 | daniel-mar | 52 | Algorithm: XOR-Shift like in version 2, but the seed is individual for |
276 | daniel-mar | 53 | each individual built standalone filter. |
54 | |||
282 | daniel-mar | 55 | The DWORD value "0x00000004" will be stored at position 0x30 (this field is not used in the `PARM` resource). |
276 | daniel-mar | 56 | |
271 | daniel-mar | 57 | ### Obfuscation "Version 3" |
58 | |||
292 | daniel-mar | 59 | Introduced in **Filter Foundry 1.7.0.5** |
267 | daniel-mar | 60 | |
61 | It is compiler-dependant, therefore the resource cannot be exchanged between plugins! |
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62 | |||
270 | daniel-mar | 63 | Algorithm: XOR with a modified `rand()`-stream with seed that is stored at position 0x30 |
267 | daniel-mar | 64 | (this field is not used in the `PARM` resource). |
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270 | daniel-mar | 66 | 32 bit plugin is built with OpenWatcom (for Win95 compatibility) which has following formula: |
67 | |||
68 | int rand_openwatcom(unsigned int* seed) { |
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69 | *seed = *seed * 1103515245L + 12345L; |
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70 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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71 | } |
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72 | |||
271 | daniel-mar | 73 | 64 bit plugin is built with Visual C++ which has following formula: |
270 | daniel-mar | 74 | |
75 | int rand_msvcc(unsigned int* seed) { |
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272 | daniel-mar | 76 | *seed = *seed * 214013L + 2531011L; |
77 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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270 | daniel-mar | 78 | } |
79 | |||
271 | daniel-mar | 80 | ### Obfuscation "Version 2" |
267 | daniel-mar | 81 | |
292 | daniel-mar | 82 | Introduced in **Filter Foundry 1.7b1** |
267 | daniel-mar | 83 | |
84 | It is compiler-independant! |
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85 | |||
86 | Algorithm: [XOR-Shift](https://de.wikipedia.org/wiki/Xorshift "XOR-Shift") with hardcoded seed `0x95d4a68f`. |
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87 | |||
88 | x32 = 0x95d4a68f; |
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89 | for(i = size, p = pparm; i--;) { |
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272 | daniel-mar | 90 | x32 ^= x32 << 13; |
91 | x32 ^= x32 >> 17; |
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92 | x32 ^= x32 << 5; |
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93 | *p++ ^= x32; |
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267 | daniel-mar | 94 | } |
95 | |||
271 | daniel-mar | 96 | ### Obfuscation "Version 1" |
267 | daniel-mar | 97 | |
98 | Introduced in **Filter Foundry 1.4b8,9,10** |
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99 | |||
100 | It is compiler-dependant, therefore the resource cannot be exchanged between plugins! |
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101 | |||
102 | Algorithm: XOR with `rand()`-stream with hardcoded seed `0xdc43df3c`. |
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103 | |||
104 | srand(0xdc43df3c); |
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105 | for(i = size, p = pparm; i--;) { |
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272 | daniel-mar | 106 | *p++ ^= rand(); |
271 | daniel-mar | 107 | } |
108 | |||
109 | The plugin is built with Visual C++ which has following formula: |
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110 | |||
111 | int rand_msvcc(unsigned int* seed) { |
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272 | daniel-mar | 112 | *seed = *seed * 214013L + 2531011L; |
113 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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271 | daniel-mar | 114 | } |
115 |