openmohaa/code/gamespy/gutil.c

/******

GameSpy / GameMaster Utility Code
  
Copyright 1998 Critical Mass Communications, LLC.

Suite E-204
2900 Bristol Street
Costa Mesa, CA 92626
(714)549-7689
Fax(714)549-0757

see gsutils.h for documentation

******/

typedef unsigned char uchar;

static void swap_byte(uchar* a, uchar* b)
{
    uchar swapByte;

    swapByte = *a;
    *a = *b;
    *b = swapByte;
}

static uchar encode_ct(uchar c)
{
    if (c < 26) return (uchar)('A' + c);
    if (c < 52) return (uchar)('a' + c - 26);
    if (c < 62) return (uchar)('0' + c - 52);
    if (c == 62) return (uchar)('+');
    if (c == 63) return (uchar)('/');

    return 0;
}

void gs_encode(uchar* ins, int size, uchar* result)
{
    int    i, pos;
    uchar  trip[3];
    uchar  kwart[4];

    i = 0;
    while (i < size)
    {
        for (pos = 0; pos <= 2; pos++, i++)
            if (i < size) trip[pos] = *ins++;
            else trip[pos] = '\0';
        kwart[0] = (unsigned char)((trip[0]) >> 2);
        kwart[1] = (unsigned char)((((trip[0]) & 3) << 4) + ((trip[1]) >> 4));
        kwart[2] = (unsigned char)((((trip[1]) & 15) << 2) + ((trip[2]) >> 6));
        kwart[3] = (unsigned char)((trip[2]) & 63);
        for (pos = 0; pos <= 3; pos++) *result++ = encode_ct(kwart[pos]);
    }
    *result = '\0';
}

void gs_encrypt(uchar* key, int key_len, uchar* buffer_ptr, int buffer_len)
{
    int counter;
    uchar x, y, xorIndex;
    uchar state[256];

    for (counter = 0; counter < 256; counter++) state[counter] = (uchar)counter;

    x = 0; y = 0;
    for (counter = 0; counter < 256; counter++)
    {
        y = (uchar)((key[x] + state[counter] + y) % 256);
        x = (uchar)((x + 1) % key_len);
        swap_byte(&state[counter], &state[y]);
    }

    x = 0; y = 0;
    for (counter = 0; counter < buffer_len; counter++)
    {
        x = (uchar)((x + buffer_ptr[counter] + 1) % 256);
        y = (uchar)((state[x] + y) % 256);
        swap_byte(&state[x], &state[y]);
        xorIndex = (uchar)((state[x] + state[y]) % 256);
        buffer_ptr[counter] ^= state[xorIndex];
    }
}