"Few false ideas have more firmly gripped the minds of so many intelligent men than the one that, if they just tried, they could invent a cipher that no one could break." (David Kahn)
The variants of encryption systems are endless. For deciphering there exists always the same game of trial and error (first guessing the encryption method, then the code). A help to do so is pruning. Once, after a more or less long or short period a code/cipher breaks. Monoalphabetic ciphers can be broken easily and of course are no longer used today but for games.
NSFNet
Developed under the auspices of the National Science Foundation (NSF), NSFnet served as the successor of the ARPAnet as the main network linking universities and research facilities until 1995, when it was replaced it with a commercial backbone network. Being research networks, ARPAnet and NSFnet served as testing grounds for future networks.
