Re: [saag] ASN.1 vs. DER Encoding

[Nico Williams <[e-mail]>]

On Tue, Mar 26, 2019 at 04:56:26PM -0500, Benjamin Kaduk wrote:
> On Tue, Mar 26, 2019 at 04:48:18PM -0500, Nico Williams wrote:
> > I wrote earlier that:
> > 
> > > And then they (rightly!) hate BER/DER/CER, so they propose inventing
> > > something new, often badly.  In this field, there is nothing new.  I'm
> > > sure even flatbuffers isn't new.
> > > 
> > > I say "rightly" because TLV encodings are just terrible.  We really do
> > > need non-TLV encodings (see below).
> > 
> > Now to back up that assertion:
> > 
> > 1) TLV encodings are bloated by nature due to being highly redundant.
> 
> Before I dig in too far to the rest, just to check: you're limiting to TLV
> encodings that are nested and still do TLV at every level of the hierarchy?
> I can't tell if you don't like things that are more like "a flat array of
> things, each of which has tag, length, and (usually not nested) value.

The former.  Specifically the BER family of encoding rules.

I indicated further down that it's not possible or easy to entirely
avoid nested lengths, but that TLV ERs necessarily have many more of
them than is absolutely necessary.

Each unnecessary length nesting is one more place where a careless or
inexperienced programmer can make a serious mistake in a hand-rolled
codec.

Sure, we should all be using Rust, and none should be hand-coding a
codec, which, if it were the case, would limit the TLV damage to bloat,
and possibly precluding on-line encoding (see further below in my post).

Bloat, however, is still a problem.

If you have tooling, then there's no use whatsoever to TLV ERs for new
protocols, and then you don't need to suffer even just the bloat.

Nico
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