What is Key space?
In [[cryptography]], the '''key space''' of an [[algorithm]] refers to the set of all possible [[Key (cryptography)|keys]] that can be used to initialize the [[Cryptography|cryptographic]] [[algorithm]]. For example, if an algorithm works using a key that is a [[string]] of 10 [[bit]]s, then its key space is the set of all [[binary numeral system|binary]] strings of length 10 bits; i.e. we have key space of size 2<sup>10</sup> = 1024. To avoid attackers from guessing the key using a [[Brute force attack|brute-force attack]], the key space is usually designed to be very large. Another needed attribute is that the key space designed to be ''flat'', having no or very few [[weak key]]s. ==Examples== The [[block cipher]] [[Advanced Encryption Standard|Rijndael/AES]] uses a key of up to 256 bits, resulting in a key space containing about 2<sup>256</sup> which is over 1.1579 × 10<sup>77</sup> keys. This makes it ''computationally infeasible'' to check each possible key by [[Brute force attack|brute force]]. In the [[DES]] block cipher, a 56-bit key is used, resulting in a relatively small key space of size 2<sup>56</sup>. The [[ROT13]] cipher is only designed to prevent people from accidentally reading messages (e.g. movie plot details). As there is no key, the key space is therefore empty. ==References== {{reflist}} {{math-stub}} [[Category:Cryptography]]