Name: lot-request
Type: request
Purpose: >
  Request a lot containing credentials for participating in an event
Response: lot
Inherits: message
Elements:
  Signature: { trust_embedded_key: true }
  Public-Key: { required: true }
  Event-Id: { required: true, type: identifier, class: event }
  Lot-Code:
    required: true
    type: string
    min_length: 3
    max_length: 64
    encryption_required: true
Notes:
  This request must be sent anonymously, i. e. with a randomly chosen
  identity. The identity and its associated keys should be deleted
  immediately after decrypting the response. If the lot code does not
  contain an event shortcode, the Event-Id element is mandatory.
Rejection-Codes:
  41: Unknown lot code
  42: Lot has been invalidated
  43: Lot has been picked up already
  44: Event does not exist
  45: Event shortcode is unknown
  46: Event status does not allow lot requests