[enhancement] change cryptography related function

A nonce is an arbitrary number used only once in a cryptographic communication, in the spirit of a nonce word. They are often random or pseudo-random numbers. Many nonces also include a timestamp to ensure exact timeliness, though this requires clock synchronization between organizations. The addition of a client nonce ("cnonce") helps to improve the security in some ways as implemented in digest access authentication. To ensure that a nonce is used only once, it should be time-variant (including a suitably fine-grained timestamp in its value), or generated with enough random bits to ensure a probabilistically insignificant chance of repeating a previously generated value. Some authors define pseudo-randomness (or unpredictability) as a requirement for a nonce.

So the nonce used for encryption should not be static, just as we described in #6 , we need to change it.

In order to generate a nonce, we must find a correct IV (Initialization Vector), and try to derive nonce from IV with time-variant or something else. This need to consistent since we use it to decrypt the data item storaged in our MongoDB.

To-do list:

[ ] | Change config encryption.nonce to encryption.iv
[ ] | Develop some time-variant methodology to generate nonce
[ ] | Develop some algorithm to derive nonce from IV or Key or something else, and storaged to somewhere secure. The nonce must not be static and changed dynamically.

pb-go / pb-go

[enhancement] change cryptography related function #7