A 16-round Feistel network is used in an algorithm that divides these things into their namesake subarrays. That method by Bruce Schneier has a less well-known successor algorithm named Twofish, where the size of these things is twice as big as the block size. A general protocol of an algorithm named for these things uses a generator g to construct a finite cyclic group of order (*) n, which results in the value of these things being g to the power of the quantity a times b. That algorithm named for these things, which involves taking (-5[1])discrete logarithms, is named after Diffie and Hellman. Carmichael’s totient function derives the “private” form of these objects in RSA (10[1])decryption. For 10 points, name these often-secret cryptographic pieces of information, used to encode or decode data. ■END■ (10[1])