serial.c

#include <string.h>

char* some_arr =
    "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

// @0x4012a2
int find_char(char* arr, char to_find) {
  int i = 0;
  for (; arr[i] != 0; ++i) {
    if (arr[i] == to_find) {
      return i;
    }
  }

  return -1;
}

// does something to your name
void sub_4012c8(char* name, char* arr) {
  char c = 0;
  char* name_start = name;

  while ((c = *name++)) {
    int res = find_char(arr, c);
    if (res == -1) {  // not found
      continue;
    }

    *name_start++ = (char)res;
  }

  *name_start = 0;  // 0 terminate the string
}

void sub_401273(char* arr, char* tmp_buffer, unsigned name_length) {
  char* arr_2 = arr + name_length;

  char c = 0;
  while ((c = *arr_2++)) {
    *tmp_buffer++ = c;
  }

  for (int i = name_length; i > 0; --i) {
    *tmp_buffer++ = *arr++;
  }

  *tmp_buffer = 0;  // zero terminate
}

void sub_4011ff(char* tmp_buffer, unsigned name_length) {
  name_length *= 4;
  if (name_length > 60) {
    name_length = 0x1E;
  }

  sub_401273(some_arr, tmp_buffer, name_length);
}

void sub_4011c0(char* name, char* result, char* tmp_buffer) {
  // i won't spoil everything
  // name is the input name
  // tmp_buffer the shuffeled buffer
}

// probably checks serial
char sub_401224(char computed, char input, char* tmp_buffer) {
  /* computed is the serial compute from your name */
  /* input is the serial that you actually input */

  char buffer[0x80];

  int computed_index = find_char(tmp_buffer, computed);
  sub_401273(tmp_buffer, buffer, computed_index);
  int input_index = find_char(buffer, input);

  return tmp_buffer[input_index];
}

// @0x4010be
void check(void* handle, char* name, char* serial) {
  sub_4012c8(name, some_arr);

  unsigned name_length = 0;
  if ((name_length = strlen(name)) == 0) {
    MessageBoxA(handle, "no name entered", /* other params*/);
    return;
  }

  if (strlen(serial) == 0) {
    MessageBoxA(handle, "no serial entered", /* other params*/);
    return;
  }

  char tmp_buffer[26 + 26 + 10] = {0};

  sub_4011ff(tmp_buffer, name_length);  // probably just shuffles the array

  char result[0x80] = {0};

  sub_4011c0(name, result, tmp_buffer);  // figure it out

  char* p_result = result;
  char* p_serial = serial;

  for (int i = name_length; i > 0; --i) {
    char r = *p_result;
    char n = *p_serial;

    char value = sub_401224(r, n, tmp_buffer);  // probably checks the serial
    if (value == *name++) {
      p_result++;
      p_serial++;
    } else {
      MessageBoxA(handle, "wrong serial", /* ... */);
      return;
    }
  }

  MessageBoxA(handle, "Serial is OK", /* ... */);
}

void _start() {
  char name[0x80] = {0};    // get from window
  char serial[0x80] = {0};  // get from window
  void* handle = GetModuleHandleA();

  // ... variables initialized here and window created

  check(handle, name, serial);  // @0x4010be
}