Семинар по реверсу - Гришаев и Островной

tasks/reverse/server/grishaev.c

@@ -0,0 +1,54 @@
+#include <stdio.h>
+#include <string.h>
+#include <time.h>
+#include <stdlib.h>
+
+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;
+}
+
+//0: [CHECKSUM] - 4 bytes
+//[
+//4:    [TIME] - 4 bytes
+//8:    [PAYLOAD + HEADER LEN] - 1 byte 
+//9:    [TYPE] - 1 byte
+//10:   [PAYLOAD LEN] - 1 byte
+//11:   [PAYLOAD]
+//]
+
+int main() { 
+   unsigned char type = 0x2A;
+   unsigned char payload[] = "g1mm3_th3_k3y";
+   unsigned char payload_len = strlen(payload);
+   
+   unsigned char *flag_payload = malloc(payload_len);
+   for (int i = 0; i < payload_len; ++i)
+           flag_payload[i] = payload[i] ^ 42;
+   
+   unsigned char packet_len = payload_len + 7;
+   time_t create_time = time(NULL);
+
+   char *packet = calloc(payload_len + 0xb, sizeof(char));
+
+   memcpy(&packet[11], flag_payload, payload_len);
+   memcpy(&packet[10], &payload_len, 1);
+   memcpy(&packet[9], &type, 1);
+   memcpy(&packet[8], &packet_len, 1);
+   memcpy(&packet[4], &create_time, 4);
+
+   int crc = MakeChecksum(packet + 4, packet_len);
+   memcpy(packet, &crc, 4);
+   
+   // Output
+   fwrite(packet, 1, payload_len + 0xb, stdout);
+
+   free(packet);
+   free(flag_payload);
+}

tasks/reverse/server/ostrovnoi.c

@@ -0,0 +1,64 @@
+#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);
+}