I\'m completely new to assembly language, and I was just wondering what the work

Question

I'm completely new to assembly language, and I was just wondering what the working programing code would be to for this program below.

Write a NASM 8086 program which will encrypt/decrypt a message.

It will do this by reading key and then using an exclusive OR operation to encrypt that character with the key.

Each character will then be pushed on the stack, keeping count of the number of characters in the message.

The end of the message will be indicated when the user presses the enter key.

At that point, the encrypted message will be popped off the stack, and displayed, character by character.

(Note: a key value of 0 will simply display the string in reverse.)

This problem can be solved by implementing the following algorithm:

repeat

                prompt the user to enter a number between 0 and 31

                enter an unsigned base 10 number from the keyboard and make it the key

until the key is between 0 and 31

initialize counter to 0

prompt user to enter the message

read a character from the keyboard

while character is not the CR character do

                char <-- char XOR key

                push char on the stack

                increment the counter

endwhile

print a CR/LF pair

for counter times do

                pop char off the stack

                display it

endfor

Note that if you enter the cyphertext with the same key used to encrypt it, you should get the original plaintext back.

Explanation / Answer

mov edi,eax //copies the value of ekey into edi

sub ecx, 0x0A //subtract 10 from the character

push ecx //push changed character onto the top of the stack - ESP

and eax,0xAA //logical and 10 with the ekey

not eax //not the ekey

mov edx,eax //move the mangled ekey into edx

mov eax,edi //move the original ekey into eax

or eax,0xAA //or the value of 10 with eax

add eax,edx //add together both mangled keys and store in eax

mov edx,eax //move the value of eax into edx

pop eax //eax = character

xor eax,edx //xor the value in edx with the ekey

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