thinQmaster Virtual testing partner Adaptive practice exams that find your weak spots and drill them. Every answer explained. From $69
Enroll

thinQmaster

Find your exam

Five questions free, before you decide.

Step 1 · choose a vendor

In one of our camps? Your practice exams come with the tuition — they are on your study page already.

Security Fundamentals & Crypto · Intermediate

Key Space

The total number of possible keys for an algorithm, equal to 2 to the power of the key length for random binary keys.

Definition

Key space determines how many guesses an exhaustive brute-force search requires. Each added bit doubles the key space. A 128-bit key space contains 2^128 possible keys, which is infeasible to search with classical computers.

Example

DES's 56-bit key space (2^56) was brute-forced in under a day by 1999.

Exam tip

Grover's algorithm effectively halves symmetric key strength against quantum attackers, so AES-256 is recommended long term.

Related terms