Brute Force Attack
Even if a symmetric cipher is currently unbreakable by exploiting structural weaknesses in its algorithm, it is possible to run through the entire space of keys in what is known as a brute force attack. Since longer symmetric keys require exponentially more work to brute force search, a sufficiently long symmetric key makes this line of attack impractical.
With a key of length n bits, there are 2n possible keys. This number grows very rapidly as n increases. Moore's law suggests that computing power doubles roughly every 18 to 24 months, but even this doubling effect leaves the larger symmetric key lengths currently considered acceptable well out of reach. The large number of operations (2128) required to try all possible 128-bit keys is widely considered to be out of reach for conventional digital computing techniques for the foreseeable future. However, alternative forms of computing technology are anticipated which may have superior processing power than classical computers. If a suitably sized quantum computer capable of running Grover's algorithm reliably becomes available, it would reduce a 128-bit key down to 64-bit security, roughly a DES equivalent. This is one of the reasons why AES supports a 256-bit key length. See the discussion on the relationship between key lengths and quantum computing attacks at the bottom of this page for more information.
Read more about this topic: Key Size
Famous quotes containing the words brute force, brute, force and/or attack:
“A chaplain is the minister of the Prince of Peace serving the host of the God of War—Mars. As such, he is as incongruous as a musket would be on the altar at Christmas. Why, then, is he there? Because he indirectly subserves the purpose attested by the cannon; because too he lends the sanction of the religion of the meek to that which practically is the abrogation of everything but brute Force.”
—Herman Melville (1819–1891)
“All generous minds have a horror of what are commonly called “facts.” They are the brute beasts of the intellectual domain. Who does not know fellows that always have an ill-conditioned fact or two that they lead after them into decent company like so many bull-dogs, ready to let them slip at every ingenious suggestion, or convenient generalization, or pleasant fancy? I allow no “facts” at this table.”
—Oliver Wendell Holmes, Sr. (1809–1894)
“‘Tis happy, therefore, that nature breaks the force of all sceptical arguments in time, and keeps them from having any considerable influence on the understanding. Were we to trust entirely to their self-destruction, that can never take place, ‘till they have first subverted all conviction, and have totally destroy’d human reason.”
—David Hume (1711–1776)
“If you attack the establishment long enough and hard enough, they will make you a member of it.”
—Art Buchwald (b. 1925)