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

[Peter Gutmann <[e-mail]>]

Nico Williams <[e-mail]> writes:

I realise this is the standard ASN.1-vs-everything-else debate that comes up
every year or so, without wanting to dig up the standard responses from every
previous time it's occurred I'll try and make just one comment:

>Now to back up that assertion:
>
>1) TLV encodings are bloated by nature due to being highly redundant.
>
>2) That redundancy is a source of errors when manually coding a codec.

It's actually the opposite, with a proper TLV encoding you can create a
simple, universal recursive-descent parser that will take any arbitrary
encoded blob and report "valid" or "not valid".  It's with the non-redundant,
or at least non-self-describing, encodings where you need to hand-roll a
parser each time any field anywhere is updated, and which can't be statically
checked like ASN.1 (meaning BER/DER) can.

>Thus there is almost zero benefit to self-describing encodings.

... apart from the fact that they can be statically analysed to check whether
they're well-formed or not, unlike the encodings in PGP, TLS, IPsec, SSH, ...

Peter.