format ELF executable

entry _start

segment readable executable

_start:	mov eax, dword ptr esp + 8
	mov dword ptr msg, eax
	cmp dword ptr msg, 00h
	je error
	push 3Eh
	xor ebx, ebx
	mov ecx, dword ptr msg
start:	mov bl, byte ptr ecx
	cmp bl, 41h
	jl skip
	cmp bl, 7Bh
	jge skip
	cmp bl, 61h
	jge lower
	cmp bl, 5Bh
	jge skip
	sub bl, 65	
	jmp over
lower:	sub bl, 61h	
over:	mov dl, byte ptr ROT13 + ebx
	mov byte ptr ecx, dl
skip:	inc ecx
	cmp byte ptr ecx, 00h
	jne start
	mov byte ptr ecx, 0Ah
	inc ecx
	mov eax, 4
	mov ebx, 1
	mov edx, ecx
	mov ecx, dword ptr msg
	sub edx, dword ptr msg
	int 80h
	mov eax, 1
	xor ebx, ebx
	jmp done
error:	mov eax, 4
	mov ebx, 1
	mov ecx, errmsg
	mov edx, 10
	int 80h
	mov eax, 1
	mov ebx, -1
done:	int 80h

segment readable writeable

msg:	dd	00h
errmsg:	db	"No input!", 0Ah, 00h
ROT13:	db	"NOPQRSTUVWXYZABCDEFGHIJKLM"