Name: message
Elements:
  Message-Type: { required: true, type: string, min_length: 3, max_length: 64 }
  Signature: { type: signature }
  From: { type: identity }
  To: { type: identity }
  Via: { type: identity }
  Partcp-Version: { type: float, min_value: 1.0, max_value: 1.0 }
  Date: { type: timestamp, min_value: now - 5 minutes, max_value: now + 5 minutes }
  Public-Key:  { type: public_key }
Rejection-Codes:
  10: Message could not be parsed
  11: Message-Type header is missing
  12: Unknown message type
  13: Invalid message structure
  71: Signature could not be verified
  72: Elements could not be decrypted