Doubly encrypted transmission between Web Historian and PDK

[lbogaardt]

The Passive Data Kit URL entries contain the encrypted_transmission field. This is a new feature to set up public/private key pairs between PDK clients (the Web Historian) and PDK servers to encrypt the data so that only the PDK server can decrypt the transmissions from its clients. This accomplishes the same basic function as certificate pinning and also provides a data protection mechanism when HTTPS might be unavailable for some reason. When this is turned on, the encrypted payloads are generally also sent via HTTPS, so the data is doubly protected, even from MITM approaches.

Currently, this is not enabled for our version of Web Historian. Perhaps this would be a good idea in the future.