Collision Resistance (CR) Should be hard to find x,x'such that h(x)h(x) -Brute-force collision search is only O(22),not O(2") -For SHA-1,this means O(280)vs.O(2160) 99 Collision Resistance (CR)  Should be hard to find x, x’ such that h(x)=h(x’) ─ Brute-force collision search is only O(2n/2), not O(2n) ─ For SHA-1, this means O(280) vs. O(2160)