[Cryptography] Silly Diffie-Hellman question using XOR

[Erwan Legrand]

On Wed, Mar 5, 2014 at 3:26 PM, Stuart Longland
<stuartl at longlandclan.yi.org> wrote:
> Anyone here have any thoughts on this?  Did I overlook something
> fundamental?

You did. DH is based on the premise that solving the discrete
logarithm problem is hard: Alice and Bob compute exponents, which is
easy, while Eve must compute a logarithm, which is thought to be hard.

In order to attack your scheme, Eve must reverse a XOR which is known
to be very easy : Eve knows A2, B2, A3 (i.e. A1^A2^B2) and B3 (i.e.
B1^B2^A2). Thus Eve knows A1 and A4 (and B1 and B4 as well) as A1 =
A3^A2^B2 and A4 = B3^A3^A2^B2.

Erwan