[popol12]

twice as difficult ? It doesn't match what you say after that

2²⁵⁶ = 2¹²⁸ * 2¹²⁸

So, isn't it rather 2¹²⁸ times more difficult ?

[H8crilA]

Security is typically measured in bits. But yes you're right, maybe I should have written "square as difficult" to be more clear :)