[VOIPSEC] Notes on ASN

[Paul E. Jones]

Kowsik,

I'm neither the author of ASN.1 nor a contributor to the work, but I've used
it quite a bit.  While there are a lot of options for encoding, nobody is
required to be an expert in all binary or ASCII encoding rules.  Nearly
every project in which I use ASN.1 uses PER.  (And, no, PER does not mean
you're on dial-up.  For the same reasons that we have RTP header
compression, SIP signaling compression, e-mail ZIP files, etc., bits on the
wire still often matter.)

>From the user's perspective, ASN.1 is not hard.  You define a syntax,
compile it, and then use libraries to encode and decode messages.  I can
create or modify a protocol, re-compile, and have it encoding/decoding in
minutes.  Further, ASN.1 fully supports older versions of the protocol
through the use of extension markers (...) in the protocol definition.  So,
I can send a newer PDU to an older system and it is properly handled.

Compare that to other protocols: how you handle backward compatibility is
entirely dependent on how you define your own way of addressing backward
compatibility.  Nearly every non-ASN.1 system has its own unique way of
extending the protocol for future revision.  Now, that is ugly.

Complexity is entirely relative and often a matter of perspective.  Very few
systems are "simple" if they actually do anything useful.  Even if the user
interface is simple, it does not mean the underlying software to support the
user is not.  The complexity in the ASN.1 specs might be a good example:
there are great tools out there that handle all of the complexity for me so
that I can get my job done.  From the user perspective, I view ASN.1 to be
very simple.

Paul

> -----Original Message-----
> From: voipsec-bounces at voipsa.org [mailto:voipsec-bounces at voipsa.org] On
> Behalf Of Kowsik
> Sent: Thursday, July 26, 2007 12:57 AM
> To: Voipsec at voipsa.org
> Subject: [VOIPSEC] Notes on ASN
> 
> More relevant here than anywhere else. I'm just amazed at how we've
> embraced complexity of systems that we really ought to be simplifying.
> 
> http://labs.musecurity.com/2007/07/25/asn-as-in-hell/
> 
> K.
> ---
> CTO, Mu Security
> http:///www.musecurity.com
> http://labs.musecurity.com
> 
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