Symmetric Cryptography

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Microsoft Corporation

September 10, 1996

Symmetric algorithms are the most common type of encryption algorithm. They are known as symmetric because the same key is used for both encryption and decryption. Unlike the keys used with public-key algorithms, symmetric keys are frequently changed. For this reason, they are referred to here as session keys.

Compared to public-key algorithms, symmetric algorithms are very fast and, thus, are preferred when encrypting large amounts of data. Some of the more common symmetric algorithms are RC4, and the Data Encryption Standard (DES).

Many modern cryptographic protocols use a combination of public-key cryptography and symmetric cryptography to obtain the benefits of both: public-key algorithms to exchange a symmetric key, and then use symmetric algorithms to quickly encrypt or decrypt data.

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