Key space

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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.

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.

[edit] Examples

The block cipher Rijndael/AES uses a key of up to 256 bits, resulting in a key space containing over 1.1579 × 10⁷⁷ keys. This makes it computationally infeasible to check each possible key by brute force.

In the DES block cipher, a 56-bit key is used, resulting in a relatively small key space of size 2⁵⁶.

The ROT13 cipher is only intended to prevent people from accidentally reading messages (e.g. movie plot details). As there is no key, the key space is therefore empty.

[edit] References and Links

^[1] Key Space Hosting - A Web Hosting Company name themself after KEY SPACE

[edit] References

1. ^ Key Space Hosting