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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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375 | daniel-mar | 6 | - Windows resource: OBFS\16\0 (previously RCDATA\16001\0) |
7 | - MacOS resource: 'obFS' 16 (previously 'DATA' 16001) |
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267 | daniel-mar | 8 | |
9 | Normal standalone filters: |
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375 | daniel-mar | 10 | - Windows resource: PARM\16\0 (previously PARM\16000\0) |
11 | - MacOS resource: 'PARM' 16 (previously 'PARM' 16000) |
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267 | daniel-mar | 12 | |
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 | |
347 | daniel-mar | 17 | // Implements Obfusc V6. |
317 | daniel-mar | 18 | // Returns a seed that needs to be stored in the executable code. |
347 | daniel-mar | 19 | uint64_t obfusc(PARM_T* pparm); |
282 | daniel-mar | 20 | |
21 | // In V1+V2: Seed is hardcoded |
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317 | daniel-mar | 22 | // In V3: Seed is in PARM (field "unknown2") |
347 | daniel-mar | 23 | // In V4-V6: Seed is in the program code and will me modified with a binary search+replace |
271 | daniel-mar | 24 | void deobfusc(PARM_T* pparm); |
25 | |||
347 | daniel-mar | 26 | ### Obfuscation "Version 6" |
27 | |||
28 | Introduced in **Filter Foundry 1.7.0.10** |
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29 | |||
441 | daniel-mar | 30 | First, the fields `unknown1`, `unknown2`, aned `unknown3` are set to 0. |
347 | daniel-mar | 31 | |
348 | daniel-mar | 32 | A 64 bit seed will be generated. |
349 | daniel-mar | 33 | On Windows, the seed is the ECMA 182 CRC64 checksum of the PARM. |
34 | On Macintosh, it stays at the default value `0x38AD972A52830517` |
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35 | (because the manipulation of the binary code is not implemented). |
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348 | daniel-mar | 36 | |
349 | daniel-mar | 37 | Then, the CRC32b checksum of the PARM will be written to `unknown1`. |
38 | |||
39 | The PARM will then be XORed with a random data stream of the lower 32 bits of the 64 bit seed. |
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347 | daniel-mar | 40 | The algorithm is the XORshift which was introcuced in obfuscation version 2. |
41 | Unlike obfuscation version 3-5, while generating and applying the random data |
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42 | stream, no bytes are skipped. |
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43 | |||
348 | daniel-mar | 44 | After this, PARM will be XORed with the 64 bit seed, |
45 | which will be ROLed by 1 bit after each byte: |
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347 | daniel-mar | 46 | |
348 | daniel-mar | 47 | uint64_t rol_u64(uint64_t value, uint64_t by) { |
48 | return value << by | value >> (sizeof(uint64_t) * 8 - by); |
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49 | } |
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50 | |||
51 | The 64 bit seed is stored in the executable. |
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52 | |||
347 | daniel-mar | 53 | The DWORD value `0x00000006` will be stored at field `unknown2` |
54 | (byte 0x30..0x33; the field is not used in the `PARM` resource). |
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55 | |||
56 | During de-obfuscation, the program will check if the checksum in `unknown1` |
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57 | matches. If it does not match, the data will be discarded. |
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58 | |||
292 | daniel-mar | 59 | ### Obfuscation "Version 5" |
60 | |||
61 | Introduced in **Filter Foundry 1.7.0.8** |
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62 | |||
63 | Obfuscation version 5 is the same as version 4, but there is a constraint |
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311 | daniel-mar | 64 | that the seed must be equal to the CRC32b checksum of the deobfuscated PARM. |
292 | daniel-mar | 65 | This is done to check the integrity of the deobfuscation. |
311 | daniel-mar | 66 | |
309 | daniel-mar | 67 | Also, the xor-shifting is intentionally incompatible with version 4 |
311 | daniel-mar | 68 | (to avoid downgrade-attacks) by XORing the initial seed with 0xFFFFFFFF. |
292 | daniel-mar | 69 | |
329 | daniel-mar | 70 | The DWORD value `0x00000005` will be stored at field `unknown2` |
71 | (byte 0x30..0x33; the field is not used in the `PARM` resource). |
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72 | |||
73 | While generating and applying the random data stream, the bytes |
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74 | 0x30..0x33 (the location where the version info is stored) are skipped, |
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75 | like in version 3. |
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76 | |||
276 | daniel-mar | 77 | ### Obfuscation "Version 4" |
78 | |||
292 | daniel-mar | 79 | Introduced in **Filter Foundry 1.7.0.7** |
276 | daniel-mar | 80 | |
81 | It is not compiler-dependant, but different between every standalone filter. |
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82 | |||
277 | daniel-mar | 83 | Windows version: |
276 | daniel-mar | 84 | The binary code of the 8BF file will be manipulated during building |
282 | daniel-mar | 85 | to store the seed into the `deobfusc()` function. |
86 | The placeholder value is `OBFUSC_V4_DEFAULT_SEED 0x52830517` |
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87 | This allows that 32-bit and 64-bit filters are "cross built". |
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276 | daniel-mar | 88 | |
277 | daniel-mar | 89 | (Theoretical) Macintosh version: |
329 | daniel-mar | 90 | Obfuscation and deobfuscation has the seed `0x52830517`, since the |
277 | daniel-mar | 91 | manipulation of the binary code is not implemented. |
92 | |||
282 | daniel-mar | 93 | Algorithm: XOR-Shift like in version 2, but the seed is individual for |
276 | daniel-mar | 94 | each individual built standalone filter. |
95 | |||
329 | daniel-mar | 96 | The DWORD value `0x00000004` will be stored at field `unknown2` |
97 | (byte 0x30..0x33; the field is not used in the `PARM` resource). |
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276 | daniel-mar | 98 | |
329 | daniel-mar | 99 | While generating and applying the random data stream, the bytes |
100 | 0x30..0x33 (the location where the version info is stored) are skipped, |
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101 | like in version 3. |
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102 | |||
271 | daniel-mar | 103 | ### Obfuscation "Version 3" |
104 | |||
292 | daniel-mar | 105 | Introduced in **Filter Foundry 1.7.0.5** |
267 | daniel-mar | 106 | |
329 | daniel-mar | 107 | A random seed is chosen and written to field `unknown2` (byte 0x30..0x33). |
267 | daniel-mar | 108 | |
329 | daniel-mar | 109 | Then, the `PARM` resource will be obfuscated by applying an XOR operation to a random data stream: |
267 | daniel-mar | 110 | |
329 | daniel-mar | 111 | unsigned char *p; |
112 | *p++ ^= (int)(rand() * 1.0 / (RAND_MAX + 1) * 256); |
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113 | |||
114 | Bytes 0x30..0x33 (the location where the seed is stored) are skipped. |
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115 | |||
116 | The `rand()` operation is compiler-dependant, and therefore the resource cannot be exchanged between plugins. |
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117 | |||
270 | daniel-mar | 118 | 32 bit plugin is built with OpenWatcom (for Win95 compatibility) which has following formula: |
119 | |||
120 | int rand_openwatcom(unsigned int* seed) { |
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121 | *seed = *seed * 1103515245L + 12345L; |
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122 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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123 | } |
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124 | |||
271 | daniel-mar | 125 | 64 bit plugin is built with Visual C++ which has following formula: |
270 | daniel-mar | 126 | |
127 | int rand_msvcc(unsigned int* seed) { |
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272 | daniel-mar | 128 | *seed = *seed * 214013L + 2531011L; |
129 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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270 | daniel-mar | 130 | } |
131 | |||
271 | daniel-mar | 132 | ### Obfuscation "Version 2" |
267 | daniel-mar | 133 | |
292 | daniel-mar | 134 | Introduced in **Filter Foundry 1.7b1** |
267 | daniel-mar | 135 | |
329 | daniel-mar | 136 | It is compiler-independent! |
267 | daniel-mar | 137 | |
138 | Algorithm: [XOR-Shift](https://de.wikipedia.org/wiki/Xorshift "XOR-Shift") with hardcoded seed `0x95d4a68f`. |
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139 | |||
140 | x32 = 0x95d4a68f; |
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141 | for(i = size, p = pparm; i--;) { |
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272 | daniel-mar | 142 | x32 ^= x32 << 13; |
143 | x32 ^= x32 >> 17; |
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144 | x32 ^= x32 << 5; |
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145 | *p++ ^= x32; |
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267 | daniel-mar | 146 | } |
147 | |||
271 | daniel-mar | 148 | ### Obfuscation "Version 1" |
267 | daniel-mar | 149 | |
150 | Introduced in **Filter Foundry 1.4b8,9,10** |
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151 | |||
329 | daniel-mar | 152 | It is compiler-dependant, and therefore the resource cannot be exchanged between plugins! |
267 | daniel-mar | 153 | |
154 | Algorithm: XOR with `rand()`-stream with hardcoded seed `0xdc43df3c`. |
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155 | |||
156 | srand(0xdc43df3c); |
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157 | for(i = size, p = pparm; i--;) { |
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272 | daniel-mar | 158 | *p++ ^= rand(); |
271 | daniel-mar | 159 | } |
160 | |||
161 | The plugin is built with Visual C++ which has following formula: |
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162 | |||
163 | int rand_msvcc(unsigned int* seed) { |
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272 | daniel-mar | 164 | *seed = *seed * 214013L + 2531011L; |
165 | return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */ |
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271 | daniel-mar | 166 | } |
167 |