<P> Symmetric ciphers are commonly used to achieve other cryptographic primitives than just encryption . </P> <P> Encrypting a message does not guarantee that this message is not changed while encrypted . Hence often a message authentication code is added to a ciphertext to ensure that changes to the ciphertext will be noted by the receiver . Message authentication codes can be constructed from symmetric ciphers (e.g. CBC - MAC). </P> <P> However, symmetric ciphers cannot be used for non-repudiation purposes except by involving additional parties . See the ISO / IEC 13888 - 2 standard . </P> <P> Another application is to build hash functions from block ciphers . See one - way compression function for descriptions of several such methods . </P>

An advantage of symmetric key is easy and fast transformation of plain text to cipher text