m_cset.inc

汇编加密文件一例。

; this file sets the last variables in the com decryptor, copies it
; from ds:100 to fs:100 and encrypts the layers in reverse order.

; in later versions, all this is done much more elegantly,
; and this is the place where a mte should be included.

  CryptBuffer proc

              call CheckReg             ; generate checksum over regstring
              call SetLastVars          ; fill variables in decryptor

              mov cx, scramlength
              push es
               push fs
               pop es
               mov di, offset cbuffer
               mov si, offset scram_b
               cld
               rep movsb                 ; move decryptor to begin buffer
              pop es


              call EncryptFile          ; crypt child
              push cs
              pop  ds
              call CryptLayer2          ; crypt layer 2 before 1
              call CryptLayer1          ; crypt layer 1 before write

              retn
         endp CryptBuffer

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  setLastVars proc                    ; set some last variables

              mov ax,0ff
              call rand_num
              mov [xor1b],al

              mov ax,0ffff
              call rand_num
              mov [xor2d],ax

              mov ax,0ffff
              call rand_num
              mov [xor3d],ax

              mov ax,0ff
              call rand_num
              mov byte ptr [xor4],al

              retn
         endp setLastVars

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  encryptfile proc

              mov si,di
              mov dx, [xor2d]
              mov bx, [xor3d]
              mov cx, [filelength]
              shr cx,1

              push fs fs
              pop  ds es

      sprong: lodsw
              add bx,0F34Ah
              xor ax,bx
              xchg ah,al
              ror ax,3
              stosw
              loop sprong

              push cs cs
              pop  ds es

              retn
         endp encryptfile


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  CryptLayer1 proc                    ; CRYPT IN BUFFER!!

              xor ax,ax
              mov si,offset xor1_e
              sub si,2
              mov di,si
              xor bx,bx
              cli
              std

              push fs fs
              pop  ds es

         x1b: lodsw                      ; encrypt first PUSH/LODS layer
              add bx,13
              xor ax,bx
              rol al,2
              xor ah,byte ptr cs:[xor1b]
              stosw
              cmp di,offset xor1_b
              ja x1b
              cld
              sti

              push cs cs
              pop  ds es

              retn
         endp CryptLayer1

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  CryptLayer2 proc                    ; CRYPT IN BUFFER!!

              mov bp,offset xor2_e
              mov al,byte ptr [xor4]

              push fs
              pop ds

       xor2e: dec bp
              xor byte ptr ds:[bp], al
              cmp bp,offset xor2_b
              ja xor2e

              push cs
              pop ds

              retn
         endp CryptLayer2


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