Before, all cypher systems have been symmetric, because the key used to make the code is also the key used to decipher the code. For example, a German receiving a message encoded by Enigma needed to have an identical Enigma machine (the same algorithm) and the same setup (the same key). British interceptors could create the algorithm easily enough from duplicating captured enigma machines, but they needed the keys to be able to decipher the Enigma code without resorting to clever complicated methods.
Symmetric Cyphers are still widely used, since we shall see later that although new methods allow asymmetric cyphers to supply us with greater security, they also reduce the speed of communication, so that symmetric cyphers are still important.
Symmetric Cyphers:
| Cipher | Security | Speed on a 486 PC | Key Length |
| DES | Medium | 400kbit/s | 56 |
| Triple DES | Good | 150kbit/s | 112 |
| IDEA | Good | 200kbit/s | 128 |
| Triple IDEA | Very Good | 100kbit/s | 256 |