Re: [TLS] TLS ALPN (rfc7301), no reserved seperator char and why is 0 no banned

Andrei Popov <> Wed, 15 April 2015 19:24 UTC

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From: Andrei Popov <>
To: Martin Thomson <>
Thread-Topic: [TLS] TLS ALPN (rfc7301), no reserved seperator char and why is 0 no banned
Date: Wed, 15 Apr 2015 19:24:20 +0000
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Subject: Re: [TLS] TLS ALPN (rfc7301), no reserved seperator char and why is 0 no banned
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Understood, but if you want to save bytes in the ClientHello (e.g. to avoid issues with certain middle boxes), then short ALPN IDs such as 0x01 become highly attractive:).

-----Original Message-----
From: Martin Thomson [] 
Sent: Wednesday, April 15, 2015 12:07 PM
To: Andrei Popov
Cc: Hubert Kario;;
Subject: Re: [TLS] TLS ALPN (rfc7301), no reserved seperator char and why is 0 no banned

On 15 April 2015 at 11:59, Andrei Popov <> wrote:
> Since the ALPN RFC allows the use of octet strings as ALPN IDs, it seems wrong to characterize non-ASCII IDs as "junk" or "crazy" values. ALPN IDs are not intended for display to the user, and don't have to consist of ASCII characters.

I was only getting into character :)  Obviously, "crazy" is subjective.  I would hope that the IETF doesn't get into the business of using the whole expressive range provided by ALPN, because that only makes it harder to use.