Input (grade 13): Some examples of popular and well-respected symmetric algorithms include Twofish, Serpent, AES (Rijndael), Blowfish, CAST5, RC4, 3DES, and IDEA.
Output (grade 10): Examples of popular symmetric cyphers include Twofish, Serpent, AES (aka Rijndael), Blowfish, CAST5, RC4, TDES, and IDEA.