# 3 Xor expressions

• Aug 2nd 2007, 07:10 AM
neel_basu
3 Xor expressions
Let + is XOR
Code:

```b + X = d c + P = e d + e = M```
Is it possible to get back b if M, X, P is Given ??
if thats not possible is it possible if c is also Given . b is not possible to Be given.
If possible please tell teh expression. and I think its possible.
And please first try to solve if c is not given .
Thanks .
• Aug 2nd 2007, 11:13 AM
galactus
Just making the subs, if M,X,c,P are given you have:

b=M-X-c-P
• Aug 2nd 2007, 11:17 AM
neel_basu
Ya I got that But trying to get that without C But no way still now
• Aug 2nd 2007, 11:19 AM
CaptainBlack
Quote:

Originally Posted by neel_basu
Let + is XOR
Code:

```b + X = d c + P = e d + e = M```
Is it possible to get back b if M, X, P is Given ??
if thats not possible is it possible if c is also Given . b is not possible to Be given.
If possible please tell teh expression. and I think its possible.
And please first try to solve if c is not given .
Thanks .

It is not possible in general to find b given M, X and P. To show this let M, X, P all be 0. Then b=d=c=e, but they can be either 1 or 0.

If c is given then

b+X=d=M+e=M+c+P

so:

b=M+c+P+X.

RonL
• Aug 2nd 2007, 11:25 AM
neel_basu
I think (I am not in touch of Maths for 2 years [I might be wrong:D])
m = d Xor e [m is given]
d = b Xor X
here to get the value of b we need to substitute d with b Xor X
and as e is not given we must substitute
but only relation of e is given is e = c Xor P
and that relates with c
we cant get rid of c .
I thought about another way also by Xoring e with c
So e Xor c = c Xor c Xor P but its not possible cause there is no other relations (only one relation) that relates with c.
So I thing Its not possible.
• Aug 2nd 2007, 11:27 AM
neel_basu
Thanks I've got it.