Write an program using on DOSBOX (saved as encrypted.ASM file) to encrypt digits

Question

Write an program using on DOSBOX (saved as encrypted.ASM file) to encrypt digits as below: input digit: 0 1 2 3 4 5 6 7 8 9 encrypted digit: 4 6 9 5 0 3 1 8 7 2 Program should accept a string consisting of digit and non digit characters. The encrypted string should be displayed in which only the digits are affected. Then user should be queried whether or not to terminate program. If 'Y' or 'y' terminate else request another input string. When you encrypt an already encrypted string you get back the original string.

this is my code:

%include "io.mac"
.STACK 100H

.DATA
str_prompt Db "Please input a string: ",0
out_msg Db " in change is ",0
query_msg Db "quit ",0

.UPDATA
   num resb 100
.CODE
.STARTUP
   PutStr str_prompt ; request a string. input
   GetStr num,100
   PutStr out_msg
   mov EBX, num  
read:

   mov AL,[EBX]
   cmp AL,0
   je done
   cmp AL,"9"
   je convert_9
   ;cmp AH,"8"
   ;je convert_8
   ;cmp AH,"7"
   ;je convert_7
   ;cmp AH,"6"
   ;je convert_6
   ;cmp AH,"5"
   ;je convert_5
   ;cmp AL,"4"
   ;je convert_4
   ;cmp AL,"3"
   ;je convert_3
   ;cmp AL,"2"
   ;je convert_2
   ;cmp AL,"1"
   ;je convert_1
   cmp AL,"0"
   je convert_0
   jmp skip
  

convert_9:
   add AL, "2"
convert_8:
   add AL, "7"-"8"
convert_7:
   add AL, "8"-"7"
convert_6:
   add AL, "2"-"6"
convert_5:
   add AL, "3"-"5"  
convert_4:
   add AL, "0"-"4"
convert_3:
   add AL,"5"-"3"
convert_2:
   add AL,"9"-"2"
convert_1:
   add AL,"6"-"1"
convert_0:
   add AL,"4"-"0"

skip:
   PutCh AL
   inc EBX
   jmp read
done:
  
   .EXIT

It shows incorrect output but I cannout figure out the problems, please fix and give me some advice,thank you

Explanation / Answer

file: encrypt.asm %include "asm_io.inc" segment .data LF equ 0Ah ENCRYPTION_KEY db '4','6','9','5','0','3','1','8','7','2' userenter db "Enter a string to encrypt: ", 0 userexit db "Terminate? (y/n) ", 0 segment .bss input resd 1 segment .text global asm_main asm_main: enter 0,0 pusha start_encrypt: mov EAX, userenter call print_string mov EBX, input read_loop: mov AL,0 call read_char mov [EBX], AL inc EBX cmp AL, LF jne read_loop dec EBX mov byte[EBX], 0 mov EBX, input process_char: mov AL,0 mov AL,[EBX] cmp AL,0 je done cmp AL,'0' jl print_encrypted_char cmp AL,'9' jg print_encrypted_char sub AL,'0' convert_num: mov DL,AL mov EAX,ENCRYPTION_KEY add AL,DL mov AL,[EAX] call print_char inc EBX jmp process_char print_encrypted_char: call print_char inc EBX jmp process_char done: call print_nl mov EAX, userexit call print_string mov EAX, 0 call read_char mov DL,AL call read_char cmp DL,'y' je fin cmp DL,'Y' je fin jmp start_encrypt fin: call print_nl popa mov eax, 0 leave ret

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