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.

Read more about Key Size: Significance, Key Size and Encryption System, Brute Force Attack, Symmetric Algorithm Key Lengths, Asymmetric Algorithm Key Lengths, Effect of Quantum Computing Attacks On Key Strength

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

“You have many choices. You can choose forgiveness over revenge, joy over despair. You can choose action over apathy.... You hold the *key* to how well you make the emotional adjustment to your divorce and consequently how well your children will adapt.”

—Stephanie Marston (20th century)

“One writes of scars healed, a loose parallel to the pathology of the skin, but there is no such thing in the life of an individual. There are open wounds, shrunk sometimes to the *size* of a pin-prick but wounds still. The marks of suffering are more comparable to the loss of a finger, or the sight of an eye. We may not miss them, either, for one minute in a year, but if we should there is nothing to be done about it.”

—F. Scott Fitzgerald (1896–1940)