;---------------------------------------------------------------------
; XORPROG - XOR program encryption, 148 bytes! - Tylisha C. Andersen
;---------------------------------------------------------------------
; Syntax: XORPROG file.com
.model tiny
.code
.186
org 100h
;---------------------------------------------------------------------
main: mov cl, ds:[80h] ; cx = command-line length (including
xor ch, ch ; the carriage return at the end)
inc cx ;
mov di, 81h ; find the first non-space character
mov al, 20h ;
repe scasb ;
lea dx, [di-1] ; dx = ptr to filename
repne scasb ; find next space
mov byte ptr [di-1], 0; set to zero
;
mov ax, 3D02h ; open the file
int 21h ;
jc error ; jump if error
xchg bx, ax ; bx = file handle
mov ah, 3Fh ; read maximum of 60K bytes from the
mov cx, 0F000h ; file into the buffer
mov dx, offset buffer ;
int 21h ; DOS call
mov cx, ax ; cx, bp = num. of bytes read
mov bp, cx ;
not ah ; make sure some bits are set in the xor byte
mov [xorbyte],ah ; set the xor byte in the decoder
;
mov si, dx ; si, di = buffer
mov di, dx ;
m_1: lodsb ; load byte
xor al, ah ; xor with the xor byte
stosb ; store byte
loop m_1 ; loop
;
mov ax, 4200h ; move back to the beginning of the file
xor dx, dx ;
int 21h ;
jc error ; jump if error
;
mov ah, 40h ; write encoded data back to file
lea cx, [bp+34] ; cx = old length + 34 (decoder length)
mov dx, offset decoder;
int 21h ; DOS call
jc error ; jump if error
;
mov ah, 3Eh ; close the file
quit: int 21h ; DOS call
ret ; return
;
error: mov ah, 9 ; output error string
mov dx, offset error$ ;
jmp quit ; return
;---------------------------------------------------------------------
error$ db 'file access error', 13, 10, '$'
decoder db 060h, 0FAh, 0BEh, 00Fh, 001h, 0BFh, 000h, 0FEh
db 057h, 0B9h, 013h, 000h, 0F3h, 0A4h, 0C3h, 0BEh
db 022h, 001h, 0BFh, 000h, 001h, 0B9h, 000h, 0FDh
db 0ACh, 034h
xorbyte db 000h, 0AAh, 0E2h, 0FAh, 061h, 0FBh, 0FFh, 0E6h
buffer:
end main
