Hey, im trying to make an assembly program which encodes a file using base64.
Anyway I have a program that works in converting the word "Man" to TWFu. Problem is it does not convert anything else but a few 3 letter words like Tan and Ban probally because of its similarity with Man. Below is a code snippet I am using to run the encode, taking 3 bytes from the read file and converting it to 4 bytes writing it to the file then grabbing another 3 bytes and doing the same thing. If anyone could help me figure out what I am doing wrong here help would be appreciated. I am completely stumped at this point and spent the weekend stuck on this one issue.
By the way this is x86 Assembly code, 16 bit. I am using Masm as my compiler.
Encode64:
;Read Input File (3 bytes)
mov ah, 3fh
mov bx, input_handle
mov cx, Buff3b;seting the size to read at a time
mov dx, offset input_pointer ;pointing the buffer where to store
int 21h
jc End_Program
;Appends a 0 if the number of bytes read is less then 3
;ax = amount of read bytes
cmp ax, 2
jne start0
mov input_pointer[2], 0
start0:
cmp ax, 1
jne end0
mov input_pointer[1],0
mov input_pointer[2],0
end0:
or ax, ax
jz done2 ;jump to done2 if ax=0
;;;;;;;;;;Convert the 3byte data into 4 byte data
;;;;;;;;;;Storing the output into a buffer for writing
B1:
mov al, input_pointer[0]
shr al, 2
add al,65d
mov output_pointer[0],al
B2:
mov ax, word ptr input_pointer[0]
xchg al, ah
shl ax, 6
shr ax, 10
add al, 65d
mov output_pointer[1], al
B3:
mov ax, word ptr input_pointer[1]
xchg al, ah
shl ax, 4
shr ax, 10
add al, 65d
mov output_pointer[2],al
B4:
mov al, input_pointer[2]
shl al, 4
shr al,2
add al, 61d
mov output_pointer[3], al
;;;;;;;;;;;;;;;;;;;;;;;;; write 4b encoded data to output file
mov cx, buff4b;set number of bye to write
mov ah, 40h
mov bx, output_handle
mov dx, offset output_pointer ;write from buffer
int 21h
jc end_program
jmp Encode64
Offline 
Marked 
