Key Space (cryptography)

Key Space (cryptography)

In cryptography, an algorithm's key space refers to the set of all possible keys that can be used to initialize it. For example, if an algorithm works using a key that is a string of 10 bits, then its key space is the set of all binary strings of length 10. i.e. we have key space of size 210 = 1024.

To avoid adversaries from guessing the key using a brute-force attack, the key space is usually designed to be extremely large. Another desirable attribute is that the key space be flat, having no or very few weak keys. If the key was selected randomly from all possible keys, on average half the key space must be searched to find the solution. However, if an attacker has some knowledge of how the key was likely selected, the search time can be far less.