PoC Polymorphic Assembly

mov al, 12h ; set the key
mov edi, codeEnd ; starting address
mov ecx, codeEnd - codeStart ; length of encrypted block

; now decrypt the code, starting from the last byte
decryptLoop:
xor byte [edi], al ; decrypt byte
dec edi ; move to the next byte
loop decryptLoop

codeStart:
; put encrypted code here
codeEnd: