Name: root-registration
Type: request
Purpose: >
  Define first ("root") participant on a new machine
Response: registration-confirmation
Inherits: message
Elements:
  Date: { required: true }
  Participant-Id: { required: true, type: identity }
  Credential: { required: true, type: string, min_length: 3, max_length: 96 }
Notes: >
  The Credential element must contain the SHA256 hash of the original
  credential which will be used for key submission.
Rejection-Codes:
  41: Root registration has already been performed
  42: Participant ID has invalid domain