Subversion Repositories filter_foundry

# Obfuscated filters

## Resource location

Obfuscated standalone filters:
- Windows resource: RCDATA\16001\0
- MacOS resource: 'DATA' 16001

Normal standalone filters:
- Windows resource: PARM\16000\0
- MacOS resource: 'PARM' 16000

## Implementation

Defined in **ff.h**, implemented in **make.c**:

    void obfusc(PARM_T* pparm, unsigned int seed);
    void deobfusc(PARM_T* pparm);

### Obfuscation "Version 4"

Introduced in **Filter Foundry 1.7.0.7** [08-Aug-2021]

It is not compiler-dependant, but different between every standalone filter.

The binary code of the 8BF file will be manipulated during building
in order to store the seed into the `deobfusc()` function.
This allows that 32 bit and 64 bit filters are "cross built".

Algorithm: XOR shift like in version 2, but the seed is individual for
each individual built standalone filter.

The value "4" will be stored at position 0x30 (this field is not used in the `PARM` resource).

### Obfuscation "Version 3"

Introduced in **Filter Foundry 1.7.0.5** [30-Jul-2021]

It is compiler-dependant, therefore the resource cannot be exchanged between plugins!

Algorithm: XOR with a modified `rand()`-stream with seed that is stored at position 0x30
(this field is not used in the `PARM` resource).

32 bit plugin is built with OpenWatcom (for Win95 compatibility) which has following formula:

    int rand_openwatcom(unsigned int* seed) {
            *seed = *seed * 1103515245L + 12345L;
            return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */
    }

64 bit plugin is built with Visual C++ which has following formula:

    int rand_msvcc(unsigned int* seed) {
            *seed = *seed * 214013L + 2531011L;
            return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */
    }

### Obfuscation "Version 2"

Introduced in **Filter Foundry 1.7b1** [20-Sep-2019]

It is compiler-independant!

Algorithm: [XOR-Shift](https://de.wikipedia.org/wiki/Xorshift "XOR-Shift") with hardcoded seed `0x95d4a68f`.

    x32 = 0x95d4a68f;
    for(i = size, p = pparm; i--;) {
            x32 ^= x32 << 13;
            x32 ^= x32 >> 17;
            x32 ^= x32 << 5;
            *p++ ^= x32;
    }

### Obfuscation "Version 1"

Introduced in **Filter Foundry 1.4b8,9,10**

It is compiler-dependant, therefore the resource cannot be exchanged between plugins!

Algorithm: XOR with `rand()`-stream with hardcoded seed `0xdc43df3c`.

    srand(0xdc43df3c);
    for(i = size, p = pparm; i--;) {
            *p++ ^= rand();
    }

The plugin is built with Visual C++ which has following formula:

    int rand_msvcc(unsigned int* seed) {
            *seed = *seed * 214013L + 2531011L;
            return (*seed >> 16) & 0x7fff; /* Scale between 0 and RAND_MAX */
    }