S2 rotate in simon

[kste]

S2 rotate in simon

[kste]

I'm not sure what you mean with S2, maybe you can elaborate on that?

[nareshmuppalaneni]

In simon round, there is a left circular shift for twice (S2)

[kste]

This function here is used to filter invalid characteristics due to the dependency of the inputs to the AND. If you look at the rotational AND on bit level you can derive such a formula.

[nareshmuppalaneni]

In Simond round getStringForSimonRound function what for this code
#More improved
command += "ASSERT({0} = (IF {2} = 0x{4} THEN BVSUB({5},0x{4},0x{6}1) ELSE BVXOR(~{1} & ~{2} & {3}, {2}) ENDIF));".format(w, StpCommands().getStringRightRotate(x_in, 7, wordsize),
x_in, StpCommands().getStringRightRotate(x_in, 14, wordsize),
"f"(wordsize / 4), wordsize, "0"((wordsize / 4)- 1));

[kste]

This was slightly changed in the latest version, so you might want to have a look at the current version.

This part computes the differential probability for one round. The if/then/else is needed to deal with the special case when you have a difference of 0xFF...FF.

[kste]

A clear description of this can now be found in http://eprint.iacr.org/2015/145