Feb 28 2000 - ASSGN2.ASM - This was an assignment from a course i took in assembly at the turn of the century.. Pretty basic stuff (as far as x86 asm goes).. Sadly I haven't done much with assembler since then other than the occasional software crack here and there..

gistfile1.asm

title Course Assignment 2 for cs205	(assgn2.asm)
 
; Alex Koralewski
; id# 0019480
; This program encrypts a string based on predefined rules
; 
.model small	; allocate 64k max for code seg & 64k for data seg
.stack 10h	; allocate 16 bytes for stack seg
 
.data
MYNAME	db	"alexzz",'$'			; name & pad, valid string
NAME_L	=	($ - MYNAME)			; calculate length macro
 
digit	db	?
 
prompt1	db	"Enter a postive, non-zero integer, for encoding: ",'$'
prompt2	db	"Encrypted string: ",'$'
prompt3	db	"Enter a postive, non-zero integer, for decoding: ",'$'
prompt4 db	"Decrypted string: ",'$'
 
; macros for ease of reading
CR	equ	0dh				; carriage return
LF	equ	0ah				; line feed
 
.code
main	proc
 
	mov	ax,@data			; load data seg addy into
	mov	ds,ax				; the data seg register
 
        mov	ah,9				; load func 9 (print string)
        mov	dx,offset prompt1
        int 21h
        
	mov	ah,1				; load function 1 (get input)
 
	int 21h					; pause (for user input)
	mov	digit,al			; save the ascii input
	sub	digit,30h			; convert ascii -> actual n
	mov	al,digit			; load n into low ax register
 
	sub	MYNAME,al			; MYNAME[0] - n
	xor	MYNAME+1,00100000b		; toggle case of MYNAME[1]
	add	MYNAME+2,al			; MYNAME[2] + n
	xor	MYNAME+3,00100000b		; toggle case of MYNAME[3]
	sub	MYNAME+4,al			; MYNAME[4] - n
	xor	MYNAME+5,00100000b		; toggle case of MYNAME[5]
	mov	al,MYNAME			; swap MYNAME[0] and MYNAME[1]
	xchg	MYNAME+1,al
	mov	MYNAME,al
	mov	al,MYNAME+2			; swap MYNAME[2] and MYNAME[3]
	xchg	MYNAME+3,al
	mov	MYNAME+2,al
	mov	al,MYNAME+4			; swap MYNAME[4] and MYNAME[5]
	xchg	MYNAME+5,al
	mov	MYNAME+4,al
		
	mov	ah,2
	mov	dl,LF
	int 21h
	mov	dl,CR
	int 21h
 
        mov	ah,9				; load func 9 (print string)
        mov	dx,offset prompt2
        int 21h
 
	mov	dx,offset MYNAME
	int 21h
	
        mov	ah,2
	mov	dl,LF				; load LF char to display
	int 21h					; display a line feed
	mov	dl,CR				; load CR char to display
	int 21h					; display a carriage return
 
        mov	ah,9
        mov	dx,offset prompt3
        int 21h
 
	mov	ah,1				; load function 1 (get input)
 
	int 21h					; pause (for user input)
	mov	digit,al			; save the ascii input
	sub	digit,30h			; convert ascii -> actual n
 
	mov	al,MYNAME			; swap MYNAME[0] and MYNAME[1]
	xchg	MYNAME+1,al
	mov	MYNAME,al
	mov	al,MYNAME+2			; swap MYNAME[2] and MYNAME[3]
	xchg	MYNAME+3,al
	mov	MYNAME+2,al
	mov	al,MYNAME+4			; swap MYNAME[4] and MYNAME[5]
	xchg	MYNAME+5,al
	mov	MYNAME+4,al
 
	mov	al,digit			; load n into low ax register
	add	MYNAME,al			; MYNAME[0] + n
	xor	MYNAME+1,00100000b		; toggle case of MYNAME[1]
	sub	MYNAME+2,al			; MYNAME[2] - n
	xor	MYNAME+3,00100000b		; toggle case of MYNAME[3]
	add	MYNAME+4,al			; MYNAME[4] + n
	xor	MYNAME+5,00100000b		; toggle case of MYNAME[5]
		
	mov	ah,2
	mov	dl,LF
	int 21h
 
	mov	dl,CR
	int 21h
        mov	ah,9				; load func 9 (print string)
        mov	dx,offset prompt4
        int 21h
 
	mov	dx,offset MYNAME
	int 21h
 
	mov	ah,2
	mov	dl,LF
	int 21h
	mov	dl,CR
	int 21h
 
	mov	ah,1				; load function 1 (get input)
	int 21h					; pause (for user input)
 
	mov	ax,4c00h			; load function 4Ch (exit)
	int 21h					; end program
 
main	endp
	end main