Packet protection is described. Data of a group of packets is concatenated with a security key and a sequence number of the packet. A hash mark of the concatenated data is calculated and sent with data or control information in a packet. If each packet has reserved bits, at least some of the packets each has data, a least a portion of the hash mark, and a header having: a first bit that indicates if the hash mark is present, and a second bit that indicates if the packet is used to determine the hash mark. Otherwise, a separate control packet is sent that contains the hash mark, a first sequence number of the group of packets, and a PDU type indicating that the control packet is an integrity protection packet for the group of PDCP packets.