Symmetrickey algorithms can be divided into stream ciphers and block ciphers. Stream ciphers encrypt the bits of the message one at a time, and block ciphers take a number of bits and encrypt them as a a single unit. Blocks of 64 bits have been commonly used; the Advanced Encryption Standard algorithm approved by NIST in December 2001 uses 128bit blocks.
Symmetrickey algorithms are generally much faster to execute electronically than asymmetric key algorithms. The disadvantage of symmetrickey algorithms is the requirement of a shared secret key.
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