I've been trying to understand how the number of rounds are picked for ciphers. There seems to be a minimum number of rounds that is analyzed for "strength" and then some security margin is added.
M. Luby and C. Rackoff showed that you need only three rounds for a Feistel network if you have sufficiently random keys; however, this is not practical in reality, which is why we have key expansions. This leads me to my questions:
How is the strength of a key schedule formally analyzed?
We have suites for random numbers, such as diehard, but I've not found a reference how key schedule strength is formalized. One could look at series of rounds through diehard, but the keys will obviously be related. Furthermore, in literature, generally it seems that the key schedule is the most ridiculed part of every cipher. I dug into Ph.D. dissertations but I didn't find anything. Any suggestions would be greatly appreciated.