A 3D graphics system uses encryption keys to decrypt received and stored texture tiles of a texture in accordance with received and stored texture tile status data which indicates whether a texture tiles is encrypted or not and which one of the encryption keys is used. The decrypted texture tiles are rendered and at least a plurality of the rendered tiles is encrypted. The encrypted rendered tiles are stored in a frame buffer. Buffer tile status data is stored which indicates whether a rendered tile is encrypted or not before storage in the frame buffer, and which one of the encryption keys has been used. The encrypted rendered tiles stored in the frame buffer are decrypted in accordance with the buffer tile status data.