; standard and basic xor encryption
BASE = 2525h

_xor:
mov edx,BASE
xor edx,25h ; just any number to encrypt
; result is 2500h
; now to retrieve the encrypted number back
; xor base by result
xor edx,BASE ; remember edx have 2500h from last xor operation
; now edx have the original number which is 25h    

; another use of xor i dont know what to call it but it can be useful to store qword values and write them later to memory location
LOW_QWORD = 0ABCDEF10h
HIGH_QWORD = 23456789h
; FULL_QWORD = 23456789ABCDEF10h

_label:
mov edx,LOW_QWORD ; store the low 32bit value
xor edx,HIGH_QWORD ; we need the result
; result is 88888899h ; the KEY
mov eax,88888899h ; store it in eax for later use

; now to get the HIGH_QWORD, xor KEY by LOW_QWORD
xor edx,LOW_QWORD ; remember edx have 88888899h and being xored by ABCDEF10 which is low qword
; the result is 23456789h = high qword

; to get the LOW_QWORD xor KEY by the HIGH_QWORD
xor edx,eax ; = eax is our key 88888899h, edx = high qword
; result is 0ABCDEF10 = low qword    

xor al,1 ; Flips the first bit    

It can be used to flip bits...

mov eax,1011b
; eax now is 1011b
xor eax,1000b
; eax now is 0011b
xor eax,1000b
; eax now is 1011b
xor eax,0001b
; eax now is 1010b
ret