네트워크 보안 수업 5일차 - 코리아 정보보안 IT학원

icmp request packet 제작

dst : 192.168.15.16

chksum

unsigned short csum ( unsigned short *buf, int nwords )

{

  unsigned long sum;

  u_short oddbyte;

  register u_short answer;

  sum = 0;

  while( nwords > 1 ) {

  sum += *buf++;

  nwords -= 2;

  }

  if( nwords ==1 ) {

  oddbyte = 0;

  *((u_char *)&oddbyte) = *(u_char *)buf;

  sum += oddbyte;

  }

  sum = (sum >> 16) + (sum & 0xffff);

  sum += (sum >> 16);

  answer = ~sum;

  return (answer);

}

raw data

90 9f 33 ec d6 e1 dst mac

90 9f 33 ec d2 ac src mac

00 08 protocol type byte ordering

Big Enddian 첫번째 바이트 부터 순서대로 네트워크

Little Enddian 거꾸로 들어가는 시스템

45 버전/헤더길이

00 서비스

26 00 byte ordering

34 12 byte ordering

00 00 flag * offset

40 ttl

01 type

20 ec chk sum

c0 a8 0f 10 src ip byte ordering

c0 a8 0f 13 dst ip byte ordering

08 00 84 ee 11 11 01 00 61 62 63 64 65 66

67 68 69 6a

#include <stdio.h>

#include <string.h>

#include <unistd.h>

#include <sys/socket.h>

#include <sys/types.h>

#include <netinet/ip.h>

#include <net/if.h>

#include <net/if_arp.h>

#include <linux/if_packet.h>

#include <linux/if_ether.h>

#include <net/ethernet.h>

#include <arpa/inet.h>

struct eth_header {

        unsigned char dst[6];

        unsigned char src[6];

        unsigned short type;

} __attribute__((packed));

struct ip_header{

        unsigned char hlen:4;

        unsigned char ver:4;

        unsigned char service;

        unsigned short total;

        unsigned short id;

        unsigned char flag;

        unsigned char offset;

        unsigned char ttl;

        unsigned char type;

        unsigned short chk;

        unsigned int src;

        unsigned int dst;

} __attribute__((packed));

struct icmp_header {

        unsigned char type;

        unsigned char code;

        unsigned short chk;

        unsigned short id;

        unsigned short seq;

        unsigned char data[10];

} __attribute__((packed));

unsigned short csum ( unsigned short *buf, int nwords )

{

  unsigned long sum;

  u_short oddbyte;

  register u_short answer;

  sum = 0;

  while( nwords > 1 ) {

  sum += *buf++;

  nwords -= 2;

  }

  if( nwords ==1 ) {

  oddbyte = 0;

  *((u_char *)&oddbyte) = *(u_char *)buf;

  sum += oddbyte;

  }

  sum = (sum >> 16) + (sum & 0xffff);

  sum += (sum >> 16);

  answer = ~sum;

  return (answer);

}

int main(int argc, char *argv[])

{

        int sock = 0;

        struct sockaddr_ll sll;

        struct eth_header eth;

        struct ip_header ip;

        struct icmp_header icmp;

        char data[sizeof( eth ) + sizeof( ip ) + sizeof( icmp )] = {0,};

        //create socket

        sock = socket(PF_PACKET, SOCK_RAW, 0);

        //socket struct

        sll.sll_family = PF_PACKET;

        sll.sll_ifindex = if_nametoindex("enp0s3");

        sll.sll_halen = 6;

        //ether header

        //target mac address

        eth.dst[0] = 0x90;

        eth.dst[1] = 0x9f;

        eth.dst[2] = 0x33;

        eth.dst[3] = 0xec;

        eth.dst[4] = 0xd6;

        eth.dst[5] = 0xe1;

        //src mac address

        eth.src[0] = 0x90;

        eth.src[1] = 0x9f;

        eth.src[2] = 0x33;

        eth.src[3] = 0xec;

        eth.src[4] = 0xd2;

        eth.src[5] = 0xac;

        //type

        eth.type = 0x0008;

        //ip header

        //ver_len

        ip.ver = 0x4;

        ip.hlen  = sizeof( ip ) >> 2;

        //service

        ip.service = 0x00;

        //total

        ip.total   = htons( sizeof( ip ) + sizeof( icmp ) );

        //id

        ip.id      = htons( 0x1234 );

        //flag & offset

        ip.flag    = 0x00;

        ip.offset  = 0x00;

        //ttl

        ip.ttl     = 0x40;

        //type

        ip.type    = 0x01;

        //chk

        ip.chk     = 0x00;

        //src ip

        ip.src     = inet_addr("192.168.15.16");

        //dst ip

        ip.dst     = inet_addr("192.168.15.19");

        ip.chk = csum( (unsigned short *)&ip, sizeof( ip ) );

        //icmp header

        //type

        icmp.type  = 0x08;

        //code

        icmp.code  = 0x00;

        //check sum

        icmp.chk   = 0x00;

        //id

        icmp.id    = htons( 0x1111 );

        //seq

        icmp.seq   = htons( 0x0001 );

        //data

        memcpy( icmp.data, "abcdefghij", 10 );

        icmp.chk = csum( (unsigned short *)&icmp, sizeof( icmp ) );

        memcpy( data, &eth, sizeof( eth ) );

        memcpy( data + sizeof( eth ), &ip, sizeof( ip ) );

        memcpy( data + sizeof( eth ) + sizeof( ip ), &icmp, sizeof( icmp ) );

        int i = 0;

        unsigned char *ptr = data;

        for( i = 0; i < sizeof( data ); i++){

                if( i != 0 && i % 16 ==0 ){ printf("\n"); }

                printf("%02x ", *(ptr+i));

        }

        printf("\n");

        //send

        sendto(sock, data, sizeof(data), 0, (struct sockaddr *)&sll, sizeof(sll));

        return 0;

}