key assignment的用法和樣例：
例句
- Users can make their public keys freely available or place them at a key distribution centre for others to access.
用戶(hù)可以讓公開(kāi)密鑰自由使用或者把公開(kāi)密鑰放在可由別人存取的密鑰分配中心。 - The private key can guarantee the security of communication, while the distribution is still a problem.
私鑰系統雖然安全，但是密鑰分配的安全性在經(jīng)典系統中一直難以得到保證。
