.model small

data segment
msg0    db 'Inserisci la parola da codificare: $'
msg1    db 'Chiave: $'
A_CAPO  db 0ah,0dh,'$'
str     db 254,0,254 DUP(' ')
strk    db 254,0,254 DUP(?)
chiave  db ?
ends

.stack

.code     

lea ax,data
mov ds,ax

   
lea dx,msg0
mov ah,09h
int 21h         ;scrive msg0

mov ah,0ah
lea dx,str
int 21h         ;legge la stringa

mov ah,09h    
lea dx,A_CAPO
int 21h
lea dx,msg1
int 21h
mov ah,01h
int 21h
mov chiave,al   ;legge la chiave
xor bx,bx
mov bl,str[1]   ;lunghezza stringa
mov strk[1],bl
xor cx,cx
mov cl,bl
ciclo:
    mov al,str[bx+1]
    xor al,chiave
    mov strk[bx+1],al
    dec bx
    loop ciclo
mov bl,strk[1]
mov strk[bx+2],'$'
mov ah,09h
lea dx,A_CAPO
int 21h
int 21h
lea dx,strk+2
int 21h
END