ctf_seminar/tasks/reverse/server/ostrovnoi.c

#include <stdio.h>
#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <string.h>
#include <time.h>
#include <stdlib.h>

unsigned int MakeChecksum(unsigned char* param_1,unsigned long param_2)
{
  unsigned int local_14;
  unsigned long local_10;
  
  local_14 = 0;
  for (local_10 = 0; local_10 < param_2; local_10 = local_10 + 1) {
    local_14 = (local_14 << 3 | local_14 >> 0x1d) ^ param_1[local_10];
  }
  return local_14;
}
//unsigned int MakeChecksum(unsigned char *buffer, int len)
//{
//  unsigned int result;
//
//  result = 0;
//  for (int i = 0; i < len; i = i + 1) {
//    result = (result << 3 | result >> 0x1d) ^ buffer[i];
//  }
//  return result;
//}

int* MakePacket(void *string,size_t str_len,char param_3)
{
  unsigned int uVar1;
  int* puVar2;
  time_t tVar3;
  
  puVar2 = (int*)calloc(1,str_len + 0xb);
                    /* Копируем из param_1 uVar2_size байт со сдвигом 11
                       байт от начала puVar2
                        */
  memcpy((void *)((long)puVar2 + 0xb),string,str_len);
  *(char *)((long)puVar2 + 9) = param_3;
  *(char *)((long)puVar2 + 10) = (char)str_len;
  tVar3 = time((time_t *)0x0);
  puVar2[1] = (int)tVar3;
  *(char *)(puVar2 + 2) = (char)str_len + '\a';
  uVar1 = MakeChecksum(puVar2 + 1,str_len + 7);
  *puVar2 = uVar1;
  return puVar2;
}

int main()
{
    int* meow;
    char* string = strdup("g1mm3_th3_k3y");
    for (int i = 0; i < 13; i++)
    {
        string[i] = string[i] ^ 42;
    }
    meow = MakePacket(string, 13, 0x2A);
    
    FILE* fp = fopen("out.txt", "w");
    fwrite((void*)meow, 1, 24, stdout);
    fclose(fp);
    free(string);
}