__u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
                 __be16 sport, __be16 dport)
{
    __u32 seq;
    __u32 hash[4];
    struct keydata *keyptr = get_keyptr();
    /*
     *  Pick a unique starting offset for each TCP connection endpoints
     *  (saddr, daddr, sport, dport).
     *  Note that the words are placed into the starting vector, which is
     *  then mixed with a partial MD4 over random data.
     */
    hash[0] = (__force u32)saddr;
    hash[1] = (__force u32)daddr;
    hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
    hash[3] = keyptr->secret[11];
    seq = half_md4_transform(hash, keyptr->secret) & HASH_MASK;
    seq += keyptr->count;
    /*
     *    As close as possible to RFC 793, which
     *    suggests using a 250 kHz clock.
     *    Further reading shows this assumes 2 Mb/s networks.
     *    For 10 Mb/s Ethernet, a 1 MHz clock is appropriate.
     *    For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but
     *    we also need to limit the resolution so that the u32 seq
     *    overlaps less than one time per MSL (2 minutes).
     *    Choosing a clock of 64 ns period is OK. (period of 274 s)
     */
    seq += ktime_to_ns(ktime_get_real()) >> 6;
    return seq;
}