Rule 128.4

Private: This level of Privacy indicates that only the controller of a card on the board or the owner of a card in any other zone may read or look at the face of the card. Example: Cards in a player's hand are owned by that player. Only that player may read or look at their faces. Example: If a player controls a facedown card at a battlefield, that player and only that player may read or look at that card's face, regardless of who owns that card.