| (I) A branch of cryptography involving algorithms that use the
same key for two different steps of the algorithm (such as
encryption and decryption, or signature creation and signature
verification). (See: asymmetric cryptography.)
(C) Symmetric cryptography has been used for thousands of years
[Kahn]. A modern example of a symmetric encryption algorithm is
the U.S. Government's Data Encryption Algorithm. (See: DEA, DES.)
(C) Symmetric cryptography is sometimes called "secret-key
cryptography" (versus public-key cryptography) because the
entities that share the key, such as the originator and the
recipient of a message, need to keep the key secret. For example,
when Alice wants to ensure confidentiality for data she sends to
Bob, she encrypts the data with a secret key, and Bob uses the
same key to decrypt. Keeping the shared key secret entails both
cost and risk when the key is distributed to both Alice and Bob.
Thus, symmetric cryptography has a key management disadvantage
compared to asymmetric cryptography.
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