# Security of bit shift in Serpent

As far I know, the Serpent cipher is the only cipher that uses legit bit shifts (<<) along with circular left shift (<<<) (correct me if I am wrong).

I have two questions on it:

1. What security advantage added by bit shift? Why is it used in the first place?

2. Does the bit shift add vulnerability in differential power attack?

As for the second point: a bit shift adds more zeros, resulting in an unbalanced bit distribution (Hamming weight biases).

• Please use the buttons if you have trouble with writing markdown. – Maarten Bodewes Dec 10 '19 at 15:41
• since the shift amount is not data or key dependent it should not introduce timing or power attack vulnerabilities – Richie Frame Dec 11 '19 at 1:56
• @RichieFrame but shift is part of round permutation, key addition between rounds will be part of permutation – hardyrama Dec 15 '19 at 13:22