Re: Explicit measurability in the QUIC wire image (was Re: Packet number encryption)

[Christian Huitema <[e-mail]>]

On 2/7/2018 2:37 PM, Christian Huitema wrote:

> Actually, it should be possible to build a maximum likelihood decoder
> for an xorshift sending pattern. You are mostly concerned with erasure
> and permutations, and you roughly know the range of probability, so you
> can see likelihood of 1, 2, 3, etc. erasures, or permutations in some
> range. Obviously, the range that you can manage depends on the length of
> the code. If you can keep the decoder synchronized, you will be able to
> measure the erasure rate. If it looses synchronization, you know that
> the error rate is truly horrendous, and that's information too. And
> xorshift codes are self synchronizing, so you will regain
> synchronization quickly.

What I had in mind was a polynomial code, such as crc32 or crc64. The
generation operation is:

    unsigned int:1 next_bit_in_pattern()
    {
        static uint32_t seed = 0xc00lcode;
        const uint32_t reminder = 0x1edc6f41;
        overflow = seed>>31;
        seed <<= 1;
        seed^= (overflow*reminder);
        return (seed&1);
    }

Writing the trellis decoder is left as an exercise for the reader...

-- Christian Huitema