# Key Size

In cryptography, key size or key length is the size measured in bits of the key used in a cryptographic algorithm (such as a cipher). An algorithm's key length is distinct from its cryptographic security, which is a logarithmic measure of the fastest known computational attack on the algorithm, also measured in bits. The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. For example, Triple DES has a key size of 168 bits but provides at most 112 bits of security, since an attack of complexity 2112 is known. This property of Triple DES is not a weakness provided 112 bits of security is sufficient for an application. Most symmetric-key algorithms in common use are designed to have security equal to their key length. No asymmetric-key algorithms with this property are known; elliptic curve cryptography comes the closest with an effective security of roughly half its key length.

### Other articles related to "key size, keys, key":

Hill Cipher - Security - Key Size
... The key size is the binary logarithm of the number of possible keys ... Thus or about is an upper bound on the key size of the Hill cipher using n × n matrices ... This is only an upper bound because not every matrix is invertible and thus usable as a key ...
Index Of Coincidence - Example
... of columns, for example seven QPWKALV RXCQZIK GRBPFAE OMFLJMS DZVDHXC XJYEBIM TRQWN… If the key size happens to have been the same as the assumed number of columns, then ... the letter identities have been permuted (shifted by a constant amount corresponding to the key letter) ... other hand, if we have incorrectly guessed the key size (number of columns), the aggregate delta I.C ...
DES-X
... complexity of a brute force attack using a technique called key whitening ... DES algorithm was specified in 1976 with a 56-bit key size 256 possibilities for the key ... One scheme to increase the key size of DES without substantially altering the algorithm was DES-X, proposed by Ron Rivest in May 1984 ...
Key Size - Effect of Quantum Computing Attacks On Key Strength
... widely conjectured to be effective against all mainstream public-key algorithms including RSA, Diffie-Hellman and elliptic curve cryptography ... computer." The general consensus is that these public key algorithms are insecure at any key size if sufficiently large quantum computers capable of running Shor's algorithm become ... Encrypted data protected using public-key algorithms can be archived and may be broken at a later time ...
Data Encryption Standard - Security and Cryptanalysis - Brute Force Attack
... method of attack is brute force — trying every possible key in turn ... The length of the key determines the number of possible keys, and hence the feasibility of this approach ... DES, questions were raised about the adequacy of its key size early on, even before it was adopted as a standard, and it was the small key size, rather than ...

### Famous quotes containing the words size and/or key:

It is very considerably smaller than Australia and British Somaliland put together. As things stand at present there is nothing much the Texans can do about this, and ... they are inclined to shy away from the subject in ordinary conversation, muttering defensively about the size of oranges.
Alex Atkinson, British humor writer. repr. In Present Laughter, ed. Alan Coren (1982)

The key word in my plays is “perhaps.”
Samuel Beckett (1906–1989)