However, once we move to the second design,

we know that the only difference is on the up of signal Z2.

And with this new design, we can see that once we have input of 0,

1 here, 1, 0, 1, 0, then the output of Z2 will

become 1 is that this is because, because X3 is 1.

[SOUND] And X1 is also 1.

So 1 plus X2 which is 0 times this 1 give us a 1.

And similarly, when the input is 11, this bit will also be 1.

And if you remember how we do the conversion from binary to decimal.

So this bit position, a 1 means 32.

So if it adds 32 to this numbers, 32 plus 68 give me 100.

32 plus 89 give me a 121.

So this are not just a magic numbers, but if you take a look at this and

then if you think further.

So this 100 happens to be the square of 10.

This 121 happens to be the square of 11.

So, that says in the second design, there's a back door.

This back door is, is in embedded intentionally.

So in this case what we have here is, both pair of 10 and 100 and 11 and

121 will become valid.

So what Alice used this system to build authentication this two entrants will be

considered valid and in that case,

the second design we can consider this as a, it has a hardware Trojan.

It's going to allow user who doesn't have access to have access to the system.