These six precepts are clearly aimed at complete perfection that even modern-day ciphers would struggle to achieve (where we can replace telegraph by computer in 问题7： condition 4).Also,the second con- dition basically says (and this is implicit in his Kerckhoffs'princi- 你学习了书上 ple displayed below)that secrecy lies in the keys and not in the ci- 的内容，现在 pher itself.Later,when we delve into modern ciphers,we will see 对这段话有什 that this is taken very seriously to- day."Key Management,"as it has come to be known,is vital since a 么体会吗？ cryptanalyst who can break a key is better off than one who knows only the cryptosystem itself