Simplification of server response

[fiestajetsam]

Originally Roughtime just sent over one, fixed cert and at some point switched to having a long lived, and an delegated cert. The current structure of server response is a few layers deep, and I'd propose a flattening out of it. If we represent it as something JSON-like, it should look as of -11 like:

{
  VER: uint32,
  PATH: Path,
  INDX: uint32,
  CERT: {
    SIG: ed25519ctx signature,
    DELE: {
      MINT: Timestamp,
      MAXT: Timestamp,
      PUBK: ed25519 public key,
    }
  },
  SIG: edd25519ctx signature,
  SREP: {
    ROOT: Root,
    MIDP: Timestamp,
    RADI: uint32
  }
}

What I propose is a slight restructure, flattening out:

{
  VER: uint32,
  PATH: Path,
  INDX: uint32,
  CSIG: ed25519ctx signature,
  CERT: {
    MINT: Timestamp,
    MAXT: Timestamp,
    PUBK: ed25519 public key
  },
  TSIG: ed25519ctx signature,
  SREP: {
    ROOT: Root,
    MIDP: Timestamp,
    RADI: uint32
  }
}

There's a few reasons for this:

• By having the time and cert signatures with distinct tags, implementers have a clearer delineation of what the tag represents, not based on it's placement in the structure
• Removes a layer of nesting, which is a tiny payload size improvement
• Existing implementations could support this and old without exclusively depending on accurate version reporting - by checking for CSIG (and DELE), validation of CERT/DELE could be handled appropriately.

[dansarie]

I'm happy with the way it currently is. If this is implemented, it should be detected through version reporting - anything else just adds complexity and weirdness.