Re: [HAM-AG] [IPv6] Request for feedback: draft-evan-amateur-radio-ipv6

I had to look up that ITU regulation, so I don't know if there's a max
length on temporary callsigns.

If you treat the callsign as a base-36 number, you could squeeze up to 11
characters into 60 bits.

If you really want to handle callsigns of arbitrary length, you could use
some of the 60-bit space for direct encodings of short (e.g. <=7
characters) callsigns and the rest of the space for the hash of longer
callsigns.

On Wed, Feb 15, 2023 at 4:13 PM Evan Pratten <ewpratten@gmail.com> wrote:

> I have personally held temporary callsigns longer than 7 characters,
> which is why I wanted to handle that.
>
> Using a more space efficient encoding scheme is an interesting idea.
> Do you know if there is a maximum length on temporary callsigns by
> chance?
>
> I'll think about doing away with the hash in favor of space-efficient
> encoding.
>
> On Wed, Feb 15, 2023 at 7:10 PM Nick Harper <nharper@nharper.org> wrote:
> >
> > Why hash the callsign at all?
> >
> > Article 19 of ITU's Radio Regulations specifies the format of callsigns,
> and they are at most 7 characters long. The ASCII representation of the
> callsign could be used to generate 7 bytes (56 bits) to use in the address
> without needing any hashing. For the exception in 19.68A (on special
> occasions, for temporary use, callsigns could be longer than 7 characters),
> a 6-bit encoding scheme could be devised so that alphanumeric callsigns up
> to 10 characters long could be encoded in 60 bits.
> >
> > On Wed, Feb 15, 2023 at 3:28 PM Donald Eastlake <d3e3e3@gmail.com>
> wrote:
> >>
> >> Hi,
> >>
> >> On Wed, Feb 15, 2023 at 3:03 PM Evan Pratten <ewpratten@gmail.com>
> wrote:
> >> >
> >> > On Wed, Feb 15, 2023 at 2:58 PM Donald Eastlake <d3e3e3@gmail.com>
> wrote:
> >> > > I'm not sure the hash even needs to be cryptographic.
> >> >
> >> > Agreed. I would call a cryptographic hash *undesierable*. Why waste
> >> > processing power hiding the callsign when you have to ID yourself
> >> > anyways?
> >> >
> >> > I am admittedly far from an expert on hashing algorithms. Donald, do
> >> > you have any suggestions that fit the properties you outlined by
> >> > chance?
> >>
> >> Indeed, I would suggest using FNV-64 truncated to the top 60 bits, See
> >> https://datatracker.ietf.org/doc/draft-eastlake-fnv/
> >>
> >> Here is an article on using FNV-32 for IPv6 flow label
> >>
> https://researchspace.auckland.ac.nz/bitstream/handle/2292/13240/flowhashRep.pdf
> >>
> >> Thanks,
> >> Donald
> >> =============================
> >>  Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
> >>  2386 Panoramic Circle, Apopka, FL 32703 USA
> >>  d3e3e3@gmail.com
> >>
> >> --
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>