Classic" encryption (with secret key)
Cryptography - Algorithms

In "classical" cryptography (i.e. with secret keys), a distinction is usually made between stream ciphers and block ciphers:

• the first operate on each unit of information; usually the bit, the binary digit ;

• the latter operate on longer, fixed-size blocks, usually of a few tens of bits.

These algorithms are widely used. They are very fast, unlike most public-key algorithms (such as RSA, described in 2.2.1