# Cipher algorithms and keys

A *cipher algorithm* is a mathematical formula designed specifically
to obscure the value and content of data. Most valuable cipher algorithms
use a key as part of the formula. This key is used to encrypt the
data, and either that key or a complementary key is needed to decrypt
the data back to a useful form.

Many cipher algorithms increase their protection by increasing the size of the keys they use. However, the larger the key, the more computing time is needed to encrypt and decrypt data. So it is important to choose a cipher algorithm that strikes a balance between your protection needs and the computational cost of protecting the data.